A MICROWAVE device that thermally remodels the cornea by transmitting energy through the epithelium and without removing any corneal tissue has begun trials in Europe to correct myopia on a first cohort of human subjects. Officials at Avedro Inc., Waltham, Massachusetts, US, expect that the procedure, which is known as Keraflex, will enter US FDA clinical trials later this year.
Avedro executives believe Keraflex may have broader patient appeal than existing refractive procedures because it is completely non-invasive and temporary. It could be commercially available in Europe in 2010. “We don’t see it as competitive to LASIK but as adjunctive to LASIK,” said Avedro CEO David Muller PhD, who years ago headed Summit Technology as it developed the first excimer laser approved by the US FDA. He expects that at least initially Keraflex will be used for patients with myopia of -4.0 dioptres or less. However, experience with the first group of non-sighted patients treated suggests that -4.0 dioptres may not be the correction limit. “In our initial study we saw patients with corrections up to -10.0 dioptres without induced astigmatism,” Dr Muller said.
Once the procedure is well understood in low to moderate myopes, patient enrolment criteria may broaden, he added. Tests so far suggest the procedure is safe, with all of corneas treated regaining complete clarity with no pain within 24 hours. “On the first day post-op, you almost can’t tell that anything has been done,” Dr Muller said. But while Keraflex technology has been under development for 15 years at Dartmouth College and has undergone extensive in vitro and in vivo tests, predictability, stability and duration of human corneal remodelling have yet to be precisely determined. “We have established that the amount of refractive correction is a function of the energy delivered. Our recent limited work has shown that if we increase the energy by ‘x’ amount, we will increase the correction by ‘y’ amount. Just as with LASIK, it will take a while to work it out, but the initial results
of intended vs. achieved and post-op UCVA have been very promising,” Dr Muller said.
Because Keraflex induces changes thermally, it is likely that treatment will regress, as it tends to with other thermal approaches including conductive keratoplasty and earlier laser-based thermal approaches, Dr Muller added. He estimates that Keraflex corrections may have a lifespan of 18 to 24 months. However, it may be possible to extend that range with collagen cross-linking technologies and we will be initiating those trials in the near future, he said. Tensioning collagen remodels cornea Keraflex works by heating collagen fibrils in the stromal layer, altering their chemical structure and causing them to contract. A controlled application of energy close to the surface centrally and peripherally creates tension within the cornea, causing it to flatten and adjust for myopia, said Avedro scientific advisor John Marshall PhD, FMedSci, Rayne Institute, Kings College, St Thomas Hospital, London, UK. Similarly, tensioning stromal fibrils deeper and more peripherally steepens the cornea to correct hyperopia, noted Prof Marshall, who held the excimer laser patent that Summit Technology developed into the LASIK procedure.
The amount of microwave energy delivered by the Avedro device, the Vedera KXS™, can be precisely controlled to achieve the desired pattern and amount of tensioning, Prof Marshall said. Microwave energy propagates between two electrodes held close to the surface of the cornea using a suction ring to maintain positioning. A surface cooling attachment protects the epithelium from thermal damage and helps control how much and how deeply thermal energy is delivered to the stroma. Total treatment time is about two seconds and the equipment required for the procedure is far less complex than for LASIK. Prof Marshall suggests that a variety of methods might be employed to extend the duration of Keraflex corrections. Once a treatment is completed, ultraviolet radiation could be used to stiffen the corneal collagen much as it does in the natural ageing process. Chemical agents might also be applied to “lock” and “unlock” collagen fibrils to permit adjustments. Avedro intends to develop these concepts, he said.
A major advantage of Keraflex is it does not weaken the cornea, said Prof Marshall. “We are not actually cutting or otherwise damaging the cornea; Keraflex produces a very subtle change.” Histological examinations show that collagen fibrils are realigned but not severed with Keraflex as they are when cutting a LASIK flap. This is important because cutting a flap in LASIK reduces the structural strength of the cornea by 25 to 30 per cent even before any tissue is ablated, Prof Marshall pointed out. Biomechanical research shows that it is the side cut of the LASIK flap that does the most damage, with de-lamination cuts reducing structural strength by only six per cent to 10 per cent. Prof Marshall allowed that LASIK has been phenomenally successful. Indeed, flap stability issues have been reduced to the point that the procedure is now approved for astronauts, fighter pilots and other active professionals at increased risk of traumatic flap displacement.
Still, the long-term impact of weakening the cornea remains uncertain, Prof Marshall said. “The clinical argument is that flaps are acceptable because we don’t see ectasia. But I am not totally interested in ectasia, I am interested in fatigue. Any engineer will tell you that if you decrease intrinsic strength of a structure by 25 to 30 per cent, you will affect its performance over time, especially if it is under dynamic stress. My question is, 20 years down the line, what is the effect of the corneal incision? We really don’t know.”
Having been intimately involved with the development and commercialisation of PRK and LASIK, both Prof Marshall and Dr Muller believe that Keraflex may have even more market potential. “Excimer laser surgery started out with PRK, and many in Europe look to PRK first because it does not require cutting a flap. Keraflex is less invasive, so even more people will want to have this procedure,” Prof Marshall said. Dr Muller pointed out that LASIK still has only about two per cent market penetration, and fear of incisions and complications are significant impediments. While the prospect of regression may seem to be a disadvantage, many patients actually see it as a plus, he added. “All the market research we have done indicates that people prefer a temporary procedure, by around four to one, because it is less threatening. We are not reducing the structural integrity of the eye with this procedure, and that is the preferred outcome from both a medical and a consumer perspective.”
March Article
May Article
I shall post more articles as I find them and add my two cents.
Sunday, August 1, 2010
Thursday, March 11, 2010
Sad story of a low myope who traded up for reading glasses.
Having worn glasses for 30 years, I was eager to shed the glasses and having spoken with many people who have had Lasik, I finally made the decision myself. I would now pay considerable sums of money to reverse what I have done.
I walked into the Lasik OR with very good corrected vision. While I needed glasses for distance and had made the permanent move to bifocals, I was able to do everything I wanted to do. I walked out of the Lasik OR with overall worse vision and will, I fear, be making adjustments for the rest of my life to accommodate the surgery. My uncorrected distance vision is good right now. I can see things afar and drive without need for any glasses. There are times when I will appreciate being able to do things without glasses. However, my near vision has been virtually destroyed. I need reading glasses to eat my meals, unless I want to look at an unrecognizable plate of fuzzy food. Working in front of a computer and at my desk, I must appear like I am a bird constantly bobbing my head to be able to read things somewhat in focus. I have pairs of reading glasses all over the place. I had to change from a combination lock at the gym because I couldn’t read the numbers. I had to give up a digital watch because I couldn’t get my arm far enough away to read the time. My fears going into the procedure were the possiblity of dry eyes, halos and star bursts – problems I was assured were remote and likely to lessen with time. While my Dr. noted that at my age I would need reading glasses, I was never advised that the procedure would actually destroy my near vision.
Lasik is essentially a cosmetic procedure that helps people avoid the inconvenience and challenges in having to use glasses or contacts. Having Lasik doesn’t necessarily eliminate those challenges and, in my case, made them much more severe. The procedure is not cheap and having to deal with the potential complications makes the cost prohibitive. Anyone considering Lasik is well advised to ask how their vision could possibly be compromised. No matter what the risk factor is, you do not want to be the one dealing with complications. Search for “Lasik regrets” on the Internet and you will get past many of the websites from Lasik facilities touting their expensive procedures and actually get to read the rather depressing stories of people who paid to harm themselves.
I walked into the Lasik OR with very good corrected vision. While I needed glasses for distance and had made the permanent move to bifocals, I was able to do everything I wanted to do. I walked out of the Lasik OR with overall worse vision and will, I fear, be making adjustments for the rest of my life to accommodate the surgery. My uncorrected distance vision is good right now. I can see things afar and drive without need for any glasses. There are times when I will appreciate being able to do things without glasses. However, my near vision has been virtually destroyed. I need reading glasses to eat my meals, unless I want to look at an unrecognizable plate of fuzzy food. Working in front of a computer and at my desk, I must appear like I am a bird constantly bobbing my head to be able to read things somewhat in focus. I have pairs of reading glasses all over the place. I had to change from a combination lock at the gym because I couldn’t read the numbers. I had to give up a digital watch because I couldn’t get my arm far enough away to read the time. My fears going into the procedure were the possiblity of dry eyes, halos and star bursts – problems I was assured were remote and likely to lessen with time. While my Dr. noted that at my age I would need reading glasses, I was never advised that the procedure would actually destroy my near vision.
Lasik is essentially a cosmetic procedure that helps people avoid the inconvenience and challenges in having to use glasses or contacts. Having Lasik doesn’t necessarily eliminate those challenges and, in my case, made them much more severe. The procedure is not cheap and having to deal with the potential complications makes the cost prohibitive. Anyone considering Lasik is well advised to ask how their vision could possibly be compromised. No matter what the risk factor is, you do not want to be the one dealing with complications. Search for “Lasik regrets” on the Internet and you will get past many of the websites from Lasik facilities touting their expensive procedures and actually get to read the rather depressing stories of people who paid to harm themselves.
Tuesday, March 9, 2010
So are you a good lasik/PRK candidate? Watch out for red flags!
Read myope's guide to whether you are a good, borderline or poor candidate. Green flags are a good sign. Proceed with caution for yellow flags and watch out for red flags, they mean you are a poor candidate despite what your surgeon says! Me and others would then recommend against lasik, but ultimately, it's your eyes and decision, none of us can stop you.
Most of us would like to reduce our dependancy on glasses. There's no free lunch as all forms of lasik, prk, iols, refractive surgery has risks. Naturally, those with good results will encourage others and those with bad results will warn others. Understand the risks and decide for yourself.
I am not a doctor. What I write is information I obtained from years of research. Please do your own research starting with my guide. Ask lots of questions and post on different message boards. Hopefully your decision is an informed one. Good luck and hope you are happy with your outcome.
1. Expectations
Green flag: You are realistic in asking to reduce your refractive error(myopia, hyperopia, astigmatism) and be less dependant on glasses. You compare your pre-op UCVA vs. your post-op UCVA and consider it a success to see less blurry without glasses.
Yellow flag: You want to be nearly free of glasses and see at least 20/30 without glasses. You are fairly picky about your vision.
Red flag: You insist on being free of glasses for a long time, if not forever and want perfect 20/20 or better UCVA. This of course is impossible, especially once you become severely presbyopic in your 40s.
Tip: As much as you hate glasses, you are better off sticking with them if perfect vision is very important to you.
Sad story: I know this lady who insisted on perfect vision and being free of glasses. She got several enhancements over a two year period and is still wearing glasses.
Green flag: Normal
Yellow flag: Mild dry eyes. PRK causes less drying than lasik.
Red flag: Moderate to severe dry eyes. Look into IOLs or stick to glasses.
3. Prescription
Green flag: Attempting to reduce or eliminate -2.75d to -5.75d of myopia.
Yellow flag: Attempting to reduce or eliminate -6d to -10d of myopia, up to -4d of astigmatism and/or up to +4d of hyperopia. It's also a yellow flag to attempt to reduce or eliminate -1.5d to -2.5d of myopia.
Red flag: Attempting to reduce or eliminate more than -10 of myopia, more than -4 of astigmatism and/or more than +4 of hyperopia. It's also a red flag to attempt to reduce or eliminate less than -1.5 of myopia.
Tip: Moderate myopia around a -4 is the most common prescription treated with lasik. Even though low myopia is more common, most low myopes see decent without glasses or with very thin glasses. To them, it's not worth the cost and risks when their vision isn't bad to begin with. High myopia is not common and not all of them are good candidates or they can't achieve a full correction.
Tip: You have to decide if a partial correction is worthwhile if your prescription is very high. Don't attempt full corrections as you are asking for trouble. Youll certainly reduce the thickness of your glasses, possibly reduce your dependancy on glasses and greatly improve your UCVA so you won't be so "blind" without your cokebottles.
Tip: hyperopic lasik does not achieve great results. Regression and complications are more common. You can't add more cornea so they remove cornea from the side to make it steeper. Correcting astigmatism is also trickier and because of the coupling effect, more likley to led to overcorrections.
Sad story: This lady was -16 and alternated between glasses and contacts. She's happy she only risked one eye because that eye is ruined. Her surgeon incorrectly thought he could fully treat such a high prescription.
4. Cornea thickness
Green flag: More than 500. Don't go below 300 with lasik, however. The flap takes out 100-150 and does *not* count towards the 300 minimum!
Yellow flag: 450-500. PRK may be an option, but don't go below 350.
Red flag: Less than 450. Look into IOLs, possibly Intacs or stick with glasses.
Tip: The more cornea you leave, the more stable your vision will be, the healthier your eyes will be and the less risk of ectasia. This is one of many reasons im choosing PRK over lasik.
Sad story: This guy ended up with only 270 microns of cornea and developed ectasia 3 years later and needs cornea transplants.
5. PresbyopiaGreen flag: Moderate or high myope going for near or intermediate vision.
Yellow flag: Moderate or high myope going for distance vision.
Red flag: Low myope -3d or less.
Tip: Ask for -1d to -1.5d undercorrection as this is the best of both worlds, not too much blur at distance nor near and no blur at intermediate. More importantly, this is insurance to greatly reduce your risk of an overcorrection. Everyone knows it's far, far, far better to be undercorrected significantly than overcorrected by any amount! I am asking for -1 myself.
Tip: If you see well from near and get a full distance correction, you will simply trade up for reading glasses. End overcorrected and youll be in bifocals. No point asking for an undercorrection if your myopia is low to begin with. Be happy your distance vision isn't bad and your near vision is good to excellent without reading glasses.
Tip: I am hearing about the NuLens IOL providing 10d of accomodation in humans. This is better accomodation than what young adults get! Preclinical trials in primates have shown an incredible 40d of accomodation! If all goes well in human clinical trials, expect availability around 2020 at a cost of $30k for both eyes.
Sad story: This guy was -2.5 and got lasik. His near vision is ruined and he wears reading glasses for everything, even eating. Even though he did achieve 20/20 distance vision, he's not happy to be fully dependant on reading glasses. He now warns all low myopes that lasik is useless if you are presbyopic or will soon become presbyopic.
6. Contact lens tolerance
Green flag: Intolerant of contacts, wear only glasses.
Yellow flag: Partial success, alternate between contacts and glasses.
Red flag: Successful wearer, rarely or never wear glasses.
Tip: If you go ahead, laser one eye at a time. You won't experience aniseikonia. If your lasik outcome is worse than what you see with contacts, don't laser the other eye. You won't be able to wear glasses however.
Tip: Stick with contacts if they work for you. The costs and risks are less than lasik despite what some say otherwise. You will also usually get better vision than lasik. Wait for better technology.
Tip: A survery states those with a bad lasik outcome are much less satisfied than glasses wearers. Contact wearers are much more satisfied than glasses wearers. Those with a good lasik outcome are much more satisfied than glasses but rate themselves as being only slightly ahead of contact wearers. Thus, you have little to gain and much to risk if you are a contact wearer.
Tip: You can pretend you have 20/20 vision all day with contacts. No one will even know you have bad vision unless you tell them. The hassles and limitations with contacts are far less than with glasses. It only takes a few minutes a day to insert, remove, clean, buy contact lens.
Sad story: She got lasik and ended up seeing worse than she did with her contacts. She wonders to herself why she even bothered getting lasik as her contacts were doing the job just fine.
Sad story: Her sister got lasik and sees worse in both eyes and her eyes are too dry to go back to contacts. She risked one eye and developed the same complications as her sister.
Green flag: Happily accepting more than 1d range. My goal is -1 and ill accept -0.5 to -2.5, giving me a 2d range.
Yellow flag: Willing to settle 0.75d or 1d range. For example, accepting +0.25 to -0.75.
Red flag: Insisting on a tiny range of 0.5d. For example, plano to -0.5.
Tip: The larger your acceptable range, the higher the odds youll end up in that 20/happy range. It's common for results to be give or take a diopter. I ask for -1 but could end up anywhere from plano to -2. If im unlucky, ill be overcorrected or extremely undercorrected.
Tip: If you are presbyopic, you may want to set your target to -0.5 at minimum. I choose -1 because this will preserve some ability to see from near without needing reading glasses all the time as well as greatly reducing the risks of overcorrection.
Tip: If you end just outside your acceptable range and close to your goal, think long and hard if you want to risk an enhancement. If I end up -2.75 or -3, this will be a difficult choice on whether to enhance or leave well enough alone. There's a rather large difference between -3 and -5. Is it worth going from -3 and hoping to end at -1 without overcorrection or other complications due to enhancement?
8. BCVA
Green flag: Seeing worse than 20/20 with correction.
Yellow flag: Being able to see 20/15 to 20/20 with correction.
Red flag: Being able to see better than 20/15 with correction.
Tip: Being able to correct to 20/10 is extremely rare. When I got my PRK laser consultation, the doctor said only 4 people have ever gotten 20/10 UCVA. About 1 in 5000 have retinas capable of 20/10 vision. Consider yourself extremely lucky if you see 20/10 with glasses and don't ever expect to see even half as good after lasik.
Sad story: He corrected to 20/10 with glasses that corrected -4 myopia, -1 astigmatism. He ended up seeing 20/30 after lasik and could only correct to 20/20 with glasses. He's very upset at how blurry everything is. Big loss from super crisp 20/10 pre lasik glasses.
Sad story: Another guy had 20/12.5 vision with -6 glasses and ended up 20/25 after lasik. Glasses could not correct him to 20/20. He said he was better off seeing 20/12.5 with thick glasses than seeing 20/25 without glasses.
9. UCVA
Green flag: Seeing worse than 20/100 without correction.
Yellow flag: Being able to see 20/50 to 20/100 without correction.
Red flag: Being able to see 20/40 or better without correction.
Tip: You can see worse after lasik than before lasik without glasses. It's insane for anyone who sees well enough to legally drive to risk their eyes. I would consider it malpractice for a surgeon to operate on anyone who sees 20/40 or better without glasses.
Tip: You are better off going without glasses if you can see well enough to function without them. It's very possible your lasik vision may be worse in quality or youll develop a complication that would cause you to be worse off than simply going without glasses.
Sad story: This guy had 20/100 vision without -1.75 glasses. He could see well from near and intermediate. Glasses gave him headaches and he rarely wore them other than for driving. Although he ended with 20/20 UCVA, he has severe dry eyes. He will also need reading glasses soon. He wished he never got lasik and just lived with 20/100 vision as it's better than severe dry eyes and needing reading glasses soon.
Sad story: This lady was -1 and 20/30 UCVA, 20/15 with glasses she wore for driving. Her optometrist recommended against lasik but she went ahead anyway. She ended overcorrected and lost a line of BCVA. She sadly realized she should have left her 20/30 well enough alone and been happy to wear glasses only for driving. Her surgeon is one everyone should avoid! That's crazy to lasik 20/30 vision!
Green flag: Absolutely hate glasses.
Yellow flag: Find glasses a minor inconvenience.
Red flag: Satisfied with glasses and don't mind them.
Tip: Some people don't mind glasses but still hate their poor UCVA. Lasik may improve your UCVA so you will have functional vision without glasses and can wear a thin pair of glasses. You won't care if you don't get 20/20 UCVA since you don't mind glasses.
Tip: Write down the reasons you desire to be less dependant on glasses. Compare those reasons with others. This may put things in perspective in deciding if lasik is worth the risk.
11. Pupil size
Green flag: Smaller than 7mm. Standard size optical zone should work, but there's no guarantee you won't lose any night vision, just the risk is reduced. Your HOAs will still increase.
Yellow flag: 7-8mm. Get an optical zone at least equal to your pupil size. The standard 6mm to 6.5mm zone is too small for you.
Red flag: Larger than 8mm. How much night vision do you want to lose? That's the question. Only proceed if night vision is totally unimportant to you. Don't expect to safely drive at night.
Tip: Many young people have pupils in the 7-8mm range. As you get older, your pupils will get smaller.
12. Age
Green flag: 21-39 years old
Yellow flag: 40-60 years old. It's also a yellow flag if you are 18-20.
Red flag: Over 60 years old. It's also a red flag if you are under 18.
Tip: If you live long enough, you will eventually develop cataracts. The average age for onset of cataracts is 65. It would make sense to skip lasik and wait till you develop cataracts. Insurance will pay for the surgery that will both remove your cataracts and correct your vision with IOLs.
Tip: Even in the 40-60 age range, you may want to consider clear lens exchange over lasik. This will save you from ever having to worry about cataract surgery down the road.
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Additional tips:
1. If possible, consider getting one eye done at a time. This works great for contact wearers who still insist on lasik. Glasses wearers will experience aniseikonia unless they get their worse eye done for a small correction and if their results are good, then do both eyes. If the results are bad, youll still be able to wear glasses and still have one good eye.
2. Never be in a hurry to get lasik. Do plenty of research and learn all the facts and risks. Lasik is not going away, not till something better comes to replace it.
3. If you are a poor candidate, rather than push ahead anyway, it's far better to wait for better technology. Don't be upset, you are avoiding the risks. Yesterday's poor candidates are today's good candidates. Todays poor candidates are tomorrow's good candidates.
4. Consider an undercorrection(anywhere from 0.5d to 2.5d) in one(monovision) or both eyes if you are presbyopic or will soon be presbyopic. You will see without reading glasses except perhaps for fine print. Great for those who spend hours reading and on the computer. Youll preserve most of your near vision. Best of all, you greatly reduce your risk of an overcorrection. An "overcorrection" might just mean ending at plano instead of hyperopic. If you do end up very undercorrected, you could either still leave well enough alone or redo(enhancement) but there is no undo as cornea tissue can't be added back.
5. If your target was plano and you end undercorrected anyway, it's often wise to leave well enough alone, this goes especially true for presbyopes who will simply trade for reading glasses. They also risk being overcorrected and ending in bifocals. Enhancements are basically rolling the dice again and ive read plenty of stories where the first lasik surgery went quite well but their 2nd try resulted in complications and lots of regret at not leaving well enough alone and accepting a thin pair of driving glasses.6. Buy a pair of +1 reading glasses and put them over your distance glasses. This is the amount of undercorrection a reputable surgeon usually won't enhance. There is too much risk of complications, including being overcorrected to bother when your vision is 20/40 or better. He will prescribe you a thin pair of -1 glasses to be worn for driving and whenever you feel like it. Be happy at -1 instead of something like -5.
7. Consider safer(less risky) options such as Intacs or PRK. They have their own risks but are the "lesser of the evils" compared to lasik. You avoid a flap, save 100-150 of cornea, get less induced HOAs, less dry eyes, less damage, less complications. The limitations are that Intacs can correct a maximum of -3 and PRK can correct a maximum of -6, unless you want to risk haze and other complications. You can consider an undercorrection, it can be a good thing anyway in keeping you out of reading glasses and reducing your dependancy on distance glasses as well as greatly improving your UCVA.
8. If you are a low myope or can see quite well without glasses, it makes sense to leave well enough alone. The risk/reward ratio would be unfavorable in your case. Plus being a low myope is great, especially when you turn 40. I wish I was a low myope like you!
9. Despite what surgeons say about 250 cornea being safe, you don't want to get below 300. Youll want a 150 flap as thin flaps are less stable and have more wrinkles. Make sure your cornea is thick enough for all this and preferably enough for at least one enhancement. See tip 7.
stories:
1. I knew a young woman who was -6 in one eye and -3 in the other who was looking to get lasik in both eyes. I suggested she could consider PRK or Intacs in the -6 eye and reduce it to -2.5(-3.25 for Intacs) It's what I would have done and leave the -3 eye alone. Eliminating anisometropia/aniseikonia and improving my vision in the bad eye would be reward enough. Being a low myope in both eyes would be desirable for maintaining good near vision, especially when you turn 40.
2. I read sad stories all the time of low myopes who are presbyopic not being properly warned that they won't reduce their dependancy on glasses, but simply trade for reading glasses. One guy was -2.5 and after he got lasik, he was upset that he lost his near vision. He said it was a waste of money and risk all for nothing and he was no better off being plano than being -2.5
3.
Introduction into this myope's life plus PRK candidacy.
Ive wanted to "fix" my eyes ever since I got my first pair of glasses at age 12.
I remember asking for laser eye surgery in my teens and my dad said I was too young. I asked again in my early 20s and begin researching RK(obsolete), lasik, PRK, Intacs, IOLs, etc. I posted on different forums about lasik and was told that lasik damages every eye and those people warning me away from lasik had gotten lasik without being fully informed of the risks and they wish they could go back to glasses. They pointed out a list of over 100 different things that can go wrong with lasik. They also said that lasik increases high order aberrations, gives worse vision than glasses(especially at night and in dim light), creates a flap that never heals, causes dry eyes, puts you at risk for ectasia, etc. In short, they scared me away from lasik.
When I mentioned PRK, they said it also damages your eyes, but they admit it's the "lesser of the evils" compared to lasik. I asked about IOLs and they said that's for those who wish to remove their cataracts. I researched IOLs and they are also being done for extreme myopes who aren't good candidates for lasik/PRK. Some say that IOLs are actually *more* risky than lasik, so it's rarely done if you are a good candidate for lasik/PRK. I do know that getting IOLs also means youll never have to worry about cataracts in the future. It robs you of all accomodation so they are best for those 40+
I also researched Intacs and again, was told even Intacs have their risks and could damage your eyes and that they were meant for keratoconus and ectasia. They said my choice was glasses or contact lenses(low risk) and there was nothing else I should even consider. I had tried contacts about 20 times but they were never comfortable for more than a few minutes. I could constantly feel them and they made my eyes dry and achy. An optometrist said I had oily tears and wasn't surprised I could never tolerate contacts.
Intacs are based on contact lense technology and from my research, they have the least risks and most benefits. The biggest advantage is that Intacs can be removed and the effects will revert back to pre-op levels. Unlike PRK, I can get Intacs in one eye first and if for any reason it doesn't work out, I can have it removed and go back to glasses without aniseikonia. Saving all my cornea leaves the options open for future technology that replaces lasik/prk.
My left eye is -5, my right eye is -4.5 and I see 20/30 with glasses. Intacs will reduce my myopia and hence reduce my dependency on glasses without needing reading glasses. I will only need glasses for distance. I spend many hours a day on the computer and won't need glasses for this after Intacs. I am surprised Intacs isn't marketed more, many people are low to moderate myopes and could benefit from Intacs with less risks than lasik and even PRK. They would have the safety net of Intacs being removable among other advantages.
I learned about stuff such as:
Though less well known, these small implants can improve vision in patients with mild to moderate myopia without the risk of permanent eye damage inherent in the tissue removal technique of LASIK. Intacs are semi-circular disks implanted in the cornea which stretch it to assume a flatter shape. Though slightly less precise than LASIK, they are removeable and replaceable, so if the patient has an unexpected over- or under-correction, the implant can be removed and another of a different size inserted to obtain the desired correction. The implants are located at the edge of the cornea, so the central visual area is completely intact and undamaged, and the strength of the cornea is undiminished, making it a better option for pilots and those who engage in contact sports where eye injury is a possibility.
Intacs are unsuitable for severe myopia and more than minor astigmatism (1.00 diopters), as the cornea can only be stretched so far. If the Intacs are removed, vision returns to its preoperative level. Aside from vision correction, Intacs are also used to treat keratoconus. Intacs are FDA approved and 10 year studies have revealed no major problems with Intacs and very few patient complaints; however, because the procedure takes more training than LASIK, there are fewer eye surgery clinics offering it. However, the Intacs website gives a list of practitioners in each state, as well a few in Canada, Europe and Mexico.
Intacs pros over PRK
1. No cornea removed, keep all 550 microns
2. Center of cornea untouched
3. Very remote chance of overcorrection(for me)
4. Maintain prolate cornea(Allegretto can do that too)
5. Intacs can be removed, keeps future options open
6. 3x faster healing time and less pain
7. Bandage contact lens for only a day
8. Faster surgery than lasik/prk
9. 60% chance of improving BCVA(for keratoconus?)
10. No risk of ectasia, makes cornea stronger
11. Can get in one eye at a time
12. Less risk of dry eyes
13. Consistant correction, litle variation
PRK pros over Intacs
1. Avoid 35mm HG vacuum for 8 seconds
2. No foreign object in eyes
3. Can correct me to -1 instead of -2
4. $2000 cheaper(hardly matters)
5. Avoid migration complication of Intacs
On another note, if I do decide on PRK, it will be with the Allegretto wavefront guided with an 8mm prolate(not oblate!) zone to match my 8mm pupils. Wavefront-guided PRK is based on aberrometry measurements and is designed to treat both spherocylinder and higher order aberrations. I don't expect a reduction in my HOAs unless they were high to begin with, ill be getting tested for this. I do suspect I have plenty of HOAs and irregular astigmatism since my left eye corrects to 20/25-20/30 and my right eye corrects 20/40. I mentioned this 5 years ago on this forum. Ive learned alot since then but still have more to learn. It's good to be informed of all the risks.
I read that results demonstrated similar wavefront outcomes in both groups in eyes with less than 0.3 microns of pre-operative higher-order aberrations (HOAs), accounting for 83 percent of eyes. Eyes with 0.3 to 0.4 microns of pre-operative HOAs demonstrated slightly more improvement with wavefront-guided treatments than with Wavefront Optimized treatments. In cases with more than 0.4 microns of HOA, it was discovered that post-operative HOAs were reduced significantly in the wavefront-guided cohort. No symptomatic increases in aberrations were observed in either cohort. Also, the Allegretto Wave is the only standard LASIK platform that has demonstrated the ability to preserve and improve low contrast acuity.
One website claims: My 20/15 rate is about 99% in these cases."
Is this 20/15 with glasses? No way UCVA, most can't even get to 20/20 as ive learned. Besides ill be happy to just be 20/20 with glasses and surprised if I get 20/15 with glasses. How do more than very few people see such tiny letters, especially when glasses minify them even further? It would be a limitation of the retina and cone density. Well that limit may actually be 20/8 but with zero HOAs which is impossible, especially after lasik/prk. Note that I am skeptical of all exaggerated claims regarding "perfect vision" and "rare complications"
I did get a lasik consultation back in 2003 but of course did more research and decided lasik was too risky. Ive been interested in Intacs back then and still am. Because Intacs are so rarely done on myopia and very few centers even offer Intacs(mainly for keratoconus) I have been looking at PRK(not lasik) and the Allegretto is the newest, best laser in America. Nothing is risk free, I am just considering my options with the least amount of risk.
Option 1:
Reduce the -5.25 in left eye to -3.25 by setting the laser for 2d of correction. I am allowing a 1d margin because the healing response among many other factors dictate this. Thus ill end at -2.25 to -4.25 but there's a small chance I can end outside this range. Still, an overcorrection is very unlikley to occur. Allowing 3+ months for left eye to heal, then reduce the right eye from -4.75 to -3.25 by setting the laser for 1.5d of correction as well as correcting my irregular astigmatism at the same time. Allow 3+ months for right eye to heal, repeat left eye with a target of -1.5d(-0.5d to -2.5d range) post prk refraction. Allow 3+ months to heal and repeat right eye to closely match whatever left eye ultimately ends up at. Retaining -1.5d of myopia(give or take) will save some cornea, greatly reduce the risk of overcorrection and greatly reduce(not eliminate, that's impossible) my dependancy on both distance and reading glasses and allow me to use the computer with no glasses!
Should I end up better than 20/20 BCVA for some strange reason, I won't be getting an enhancement and will be happy to live with around -3d of myopia and enjoy the super sharp BCVA as well as reduced dependancy on glasses and never need reading glasses.
Should the first go of PRK on the left eye get me to -2.5 or better, an "overcorrection" to be technical, I won't repeat the left eye and just do the right eye to closely match the left eye. Ill be happy I didn't go for plano as I would have ended up significantly overcorrected for real. This would mean reading glasses or bifocals for me.
Should the results be dissatisfactory on the left eye regarding dryness, night vision, unusual outcome, complications, I won't touch the right eye. Because the difference between -3.25(therebouts) and -4.75 will be fairly close, this will minimize the aniseikonia and ill be able to go back to glasses and wait 5-10 years for better laser technology.
I would have to decide what action to take for other possible outcomes once they happen.
Option 2: Reduce the -5.25 in left eye to -3.25 by setting the laser for 2d of correction. I am allowing a 1d margin because the healing response among many other factors dictate this. Thus ill end at -2.25 to -4.25 but there's a small chance I can end outside this range. Still, an overcorrection is very unlikley to occur. Allowing 3+ months for left eye to heal, then reduce the right eye from -4.75 to -1.5(therebouts) with as little astigmatism as possible. Wait then do a second round on the left eye to closely match right eye. Will likley end up somewhere between -0.5 and -2.5 which is allowing a 1d margin from the -1.5d target. This range is acceptable in reducing my dependancy on glasses while keeping a low amount of myopia to preserve some near vision.
As to the possible outcomes that should happen, see above.
Option 3: Get both eyes done with a target of -1.5, range of -0.5 to -2.5. This is more risky for several reasons. Although it means no enhancements, there's a small chance of an overcorrection because I have no idea on the healing response. Ill be removing around 100 microns of cornea(27 per diopter for 8mm prolate zone?) so this puts me at increased risk of haze(even with MMC?) vs. removing around 50 microns each go and spreading it over 2 treatments, allowing a full healing each time. Ill be risking both eyes at once instead of one. Ill also lose the advantage of seeing thru the other eye when the treated eye is healing and vision may be slightly blurry.
Monovision is not for me, I do not want anisometropia nor risk overcorrecting the dormant distance eye, seen it happen all the time. I can't and won't aim for plano in either or both eyes for the reasons I mentioned, it's too risky and pointless to waste cornea just to trade for reading glasses. I use my eyes for near more than distance and am wearing computer glasses that correct 3.5d of my 5d of myopia. It is not realistic to expect an elimination of glasses for everything, you can choose distance, intermediate or near and wear glasses part time.
Choosing distance is the most risky because an overcorrection will result in bifocals. You can't add cornea back. Choosing intermediate to the tune of -1.5d gives me a safety margin. An "overcorrection" will likley mean ill be -0.5d instead of hyperopic. An undercorrection will mean ill be -3d and can either leave well enough alone or enhance that to around -1.5d. Choosing near is great for high myopes who just don't have enough cornea for any other choice anyway unless they want to risk IOLs. It's great to be around -2.5d instead of the -6, -7, -8(therebouts) that they are. If they don't find -2.5d acceptable and they don't want to risk IOLs, it's perfectly acceptable for them to stick with glasses like this -9d friend I know.
Thanks for reading. I am still doing research and have realistic expectations of a reduced dependancy on glasses, reducing my refractive error and understanding the risks.
edit:
1. How much cornea is removed for an 8mm optical zone? Where can I find the math?
2. I read that the cornea can't be flatter than 35d or the quality of vision goes way down. Is the flattening based on how much cornea is removed regardless of optical zone size or by how many diopters you correct?
3. Is it true the more cornea you remove, the more surface nerves that control tears get damaged? I notice lasik causes way more dry eyes than PRK, is this because the flap damages an extra 150 microns of cornea?
4. Why don't more people consider the Allegretto for PRK and to keep their corneas prolate? It's less risky and causes less damage than oblate lasik.
5. Why don't more people research something as serious as laser surgery as carefully and as long as me?
6. What kind of tests other than measuring my pupils(8mm?), dry eyes, cornea thickness(550 microns) HOAs, cornea topography should I ask for?
On March 25, I went to get a PRK consultation. I got several tests and asked more questions than anyone else. The optometrist says I probably know more about some aspects of vision than he does! First I was tested on the autorefractor which thinks im a -7 I told her it overcorrected me and she says that's common. Next I got topographies of my cornea. I knew I had irregular astigmatism from the 2005 topographies. Those also showed irregular astigmatism.
Then it was off to test my UCVA. I saw nothing on the eyechart, not even the 20/400 "E". I knew it probably would be an "E" since most eyecharts use this letter on top but I don't go by memory! I didn't think id see 20/400 being a -5 which is moderately high myopia. Throw in around -1 of astigmatism on top of the -5 myopia and you are talking 20/800 being in the ballpark. Then I tested with my computer glasses(-3.5) and saw 20/100 with them. With my distance glasses I see 20/30 in left eye and 20/60 in right eye. My right eye is a little undercorrected, it can do 20/30 BCVA.
This eyechart has 20/400, 200, 100, 80, 70, 60, 50, 40, 30, 25, 20, 15, 10 lines. Some eyecharts have additional lines such as 20/300, 20/250, 20/150, 20/120, 20/12, etc. I had asked him how rare 20/12 was and they don't have that line on their chart. Funny how 70% get 20/15, yet less than 0.1% get 20/10. Wonder what % would be in between.
My aberrometry showed a RMS of .38um in left and .55um in right. I was correct when I figured my right eye is more aberrated. My vision is not as clear in that eye. I also have more astigmatism as well. I would benefit from wavefront guided PRK since im above .3um They say my HOAs could be reduced to normal, but not eliminated alltogether which I already knew.
My pupils do measure in the 8mm range which I already knew. I was surprised that they give everyone the same 6.5mm optical zone with a blend to 9.2mm. This will take 16um/diopter. They say they can correct astigmatism together with myopia no problem. Even my low astigmatism can be corrected(rather, reduced) with a best fit oval ablation profile. I asked about the 8mm optical zone and he says they don't do this as it "eats" too much cornea and there's no room for a blend zone (it would be 12mm) if an 8mm optical zone were to be used. Also a blend zone is important for a smooth transition and it's better than a larger optical zone with no room for any blend zone. He says 1 in 25 people have pupils my size. There's only been one case of poor night vision under the allgretto laser with unknown cause.
He says I can aim for a -1 or -1.5 or anything I feel like. This will greatly reduce the risk of an overcorrection to hyperopia. Ill also save several microns of cornea. I said 350 microns was the safe minimum and he said I am absolutely correct. Get too thin and you get ectasia. Ill have to wear a thin pair of distance glasses for TV and driving but I get to see clearly without reading glasses for everything. I have the accomodation of a 40-45 year old and wear -3.5s for the computer and -5s for distance. Ill probably go for -1 and regress slowly over the years. Ill become more myopic as I get older, said my optometrist. No problem, ill need more myopia as my presbyopia worsens to preserve my near vision and stay out of reading glasses. I spend 75% of my time wearing my -3.5 glasses and only 25% wearing my -5 glasses so this makes sense.
They had a near chart and I was seeing 20/40 with my -5 distance glasses and 20/25 with my -3.5 computer glasses. This is from 16 inches. I have to take my glasses off and look from 8 inches to see the tiny 20/20 line. I can live with 20/25 near vision. I don't get 20/20 distance vision either as the 20/20 line is far too tiny. He says some people see better after lasik/prk than they do with their glasses. I said glasses minify and distort and he says im correct. They may see 20/25 with glasses and get 20/20 after the surgery. If they see 20/20 with glasses, they could be 20/15 after surgery!
He says there's a 97% chance of 20/20, 70% chance of 20/15 and less than 0.1% chance of 20/10! Of the 16,000+ laser surgeries performed only 4 people have ever attained a 20/10 UCVA! I said I read on the internet that 1 in 500 see 20/10 and he said try 1 in 5000! He explained that you need a superb retina and absolutely no refractive error. The exception is a small amount of hyperopia that can be accomodated by a young, non presbyopic eye. The retina limits most people to 20/15 or 20/20, but not everyone's retina will be capable of 20/20, if so, they won't be 20/20 after surgery, not even with glasses.
He says you can be 20/20 with -0.25 but he's never seen a -0.5 attain 20/20 without glasses. No one with 20/20 UCVA can be -0.5, anyone who says so is wrong and measured it wrong. He went on to say that -1 gives you 20/40 to 20/50 and -1.5 gives 20/60 to 20/80 in most of the patients he's refracted. Would be interesting to learn more about the correlation between diopters and 20/xx.
I had thought the chance was 10% of getting to plano and 67% chance of give/take half diopter and 90% chance of give/take one diopter and he says that's wrong, the odds are very, very good of 20/20 UCVA after surgery. He says young people are deliberately overcorrected to +0.25 to account for regression in the future. Also those with a spherical equivalent of plano or a quarter diopter can still see 20/20.
My corneal thickness was measured at 570 and 563, no problem for PRK nor lasik for the matter. I am choosing PRK because the risks are less. I know there's a long healing period and I read lasik is more popular because people want near instant gratification. He said im correct and also explained ill need to wear bandage contact lens for 3-5 days and expect 4-8 week healing period. I am fine with this. When I asked if I should get one eye done at a time, he said they won't be in balance and that the risk is the same for getting one or both eyes done. Guess ill get both eyes done at the same time and aim for a -1 sphere, 0 cylindar and ill end up somewhere in that ballpark.
I will be doing more research and asking more questions. The surgeon has my medical records and will be reviewing it and letting me know the best options and risks once he returns from vacation. I heard I was a candidate but I still want to learn more even though I know plenty. I also need other opinions from other laser centers.
I got a PRK candidacy test at another center:
First, I filled out a lasik checklist. A few of the questions stood out and I am reposting them here as it's informative. Q: Would you be satisfied if your natural vision was greatly improved even if you still had to wear corrective lenses some of the time? A: Yes. Q: Do you feel that good vision without glasses is more important than perfect vision with glasses? A: Yes. Q: Is it acceptable to you that you may need glasses for reading after lasik? A: No.
They are pointing out that lasik(or PRK) can reduce your dependancy on glasses. I expect my natural(UCVA) vision to be greatly improved, which should be easy since im about 20/800! I don't have perfect 20/20 vision with glasses anyway and besides, presbyopes can *not* have perfect vision, they must choose to either see well at distance or at near. If they want both, progressive glasses would be the way to go. Because I can see clear from near, why should I give that up? I am aiming for a -1.5 target so I greatly improve my distance vision while still keeping most of my near vision. Ill be able to see the computer and regular size print without readers. I already wear computer glasses most of the time and only switch to distance glasses when I get out of the house.
The usual battery of tests were done on me, same as the first PRK center. This wavefront test(6.5mm diameter) says I have a half micron of HOAs. It also says I have almost -6d of spherical equivalent. I am more like a -5.5 though. I also got an orbscan that shows the color contours and estimated my cornea at ~550 which is average thickness.
I asked lots of questions and the doctors were impressed with how knowlegeable I am. A female optometrist measured my pupils at between 8mm and 9mm. She gave me a nearvision card and I could read line 5(20/50?) with glasses and without them, I could easily see the smallest line from about 8 inches. She is 43 and presbyopic herself but thanks to being -0.75, she does not yet need reading glasses(her friends are so jealous!) and only needs "cheaters" for night driving. I figured her UCVA was 20/30 and was correct. Her BCVA is an amazing 20/15!
My BCVA is 20/25 to 20/30, the 20/20 line is simply too small because my glasses minify. If you can still see 20/20 with eyes as bad as mine, you have an amazing retina! She did say that I would be surprised by how some people can actually see better than 20/20. I certainly am surprised! The 20/20 line is tiny, just a third of an inch! With my glasses, it's much smaller than that!
I got to meet the surgeon and he was also impressed by how much I knew. He discussed monovision but it's not for me due to anisometropia. I mentioned that I am aiming for a slight undercorrection of -1.5 to preserve some of my near vision and will accept the occasional need for distance glasses. I don't drive and spend alot of time on the computer. He says the laser is accurate to 0.12 diopters and most people end within 0.25 diopters. Get me in the ballpark of -1.5 give or take half diopter and ill be happy. He says I have realistic expectations and am almost certain to achieve that. There's always the option for an enhancement. Ill probably leave well enough alone unless I end up hyperopic or very undercorrected like a -3.
Speaking of expectations, he says alot of people have high expectations and they insist on "perfect" vision. I said they are being unrealistic. If they are presbyopic, they will never be free of glasses and will never see clearly both distance and near. Monovision lets you see clear but with only one eye at a time which isn't for me. I also asked if you reject those who demand "perfect" vision and he laughed and gestured with his foot "I kick them out like this" and swung his leg. My dad later told me he was joking. I told dad that unhappy patients are bad for business because they warn their friends away.
We discussed the fear of overcorrections and he said it's rare to be overcorrected or end up with a large undercorrection. His nomogram actually programs the laser for +0.25 or even +0.5 overcorrection for young people and an undercorrection by the same amount for old people. He will program the laser so ill initally be -1 sphere then ill heal to -1.5. I said even if I end at -1, that's fine with me. There's a 1.5 diopter "buffer" before I end up hyperopic, something that would result in bifocals for presbyopes or rolling the die again on an enhancement. End up slightly undercorrected and no problem, you get to see clear from near and only need glasses for stuff like driving, watching movies and seeing things from a mile away.
We also discussed the fact the Allegretto laser is the only laser that is capable of a prolate profile. This is important for preserving quality of vision and giving the best possible night vision. An oblate ablation results in poorer quality of vision. Also this laser has a blend/transition zone to 9.2mm which results in less of a decrease in night vision compared to older lasers with a small ablation zone and no transition zone. Due to my huge pupils, I expect some decrease in night vision netherless. Ill probably be seeing some halos in the transition zone area. Another reason "perfectionists" should stick with glasses.
He asked if I wore contacts which I replied that I tried them about 20 times and they caused discomfort, irritation, dryness and felt like an eyelash. That's why im considering PRK to improve my vision and be less dependant on glasses. A note to you contact lens wearers, stick with contact lens. They do the job better than laser surgery for less cost and risk. You will be able to see without distance glasses by wearing contact lenses.
He will remove my epithelium with alcohol and a scalpel/brush. He used to do LASEK but it was no better than PRK. 80% of his surgeries he performs are LASIK and 20% are PRK. I correctly said that's because people want near instant gratification and heal in days, not weeks. PRK has less risks and gives better long term results. In exchange, I will endure wearing uncomfortable bandage contacts for 5 days, then deal with fluctuating vision for a few weeks before I fully heal and my vision stabalizes around a -1.5
Wavefront optimized vs. guided was discussed and he says wavefront guided can reduce my HOAs from 0.5um to 0.4um while wavefront optimized may increase them by 0.1 or 0.2 but that I won't notice a difference, especially since ill have -1.5d of blur anyway. He recommends wavefront guided if your HOAs are 0.8um or higher. His laser only does wavefront optimized so youd need to get it done in a different center. I will have to research this more, but I would prefer wavefront guided for myself if I can find a nearby center. It would give me a better chance of preserving more of my night vision.
Thanks for reading my long post regarding what went on during my PRK evaluation. What else should I know of? Anything you wish to share yourself?
Update(Dec 29, 2010) I haven't gotten around to this in a while but at this point im going to wait for Keraflex as well as better lasers(such as the IVIS) to come to a location near me. The PRK center with the custom wavefront Allegretto rejected me as a candidate because I knew too much and asked too many questions! Oh well, their loss as I might have gone ahead back then. The other center also has the Allegretto laser but they don't offer custom wavefront. No thanks, I don't want an increase in HOAs.
I remember asking for laser eye surgery in my teens and my dad said I was too young. I asked again in my early 20s and begin researching RK(obsolete), lasik, PRK, Intacs, IOLs, etc. I posted on different forums about lasik and was told that lasik damages every eye and those people warning me away from lasik had gotten lasik without being fully informed of the risks and they wish they could go back to glasses. They pointed out a list of over 100 different things that can go wrong with lasik. They also said that lasik increases high order aberrations, gives worse vision than glasses(especially at night and in dim light), creates a flap that never heals, causes dry eyes, puts you at risk for ectasia, etc. In short, they scared me away from lasik.
When I mentioned PRK, they said it also damages your eyes, but they admit it's the "lesser of the evils" compared to lasik. I asked about IOLs and they said that's for those who wish to remove their cataracts. I researched IOLs and they are also being done for extreme myopes who aren't good candidates for lasik/PRK. Some say that IOLs are actually *more* risky than lasik, so it's rarely done if you are a good candidate for lasik/PRK. I do know that getting IOLs also means youll never have to worry about cataracts in the future. It robs you of all accomodation so they are best for those 40+
I also researched Intacs and again, was told even Intacs have their risks and could damage your eyes and that they were meant for keratoconus and ectasia. They said my choice was glasses or contact lenses(low risk) and there was nothing else I should even consider. I had tried contacts about 20 times but they were never comfortable for more than a few minutes. I could constantly feel them and they made my eyes dry and achy. An optometrist said I had oily tears and wasn't surprised I could never tolerate contacts.
Intacs are based on contact lense technology and from my research, they have the least risks and most benefits. The biggest advantage is that Intacs can be removed and the effects will revert back to pre-op levels. Unlike PRK, I can get Intacs in one eye first and if for any reason it doesn't work out, I can have it removed and go back to glasses without aniseikonia. Saving all my cornea leaves the options open for future technology that replaces lasik/prk.
My left eye is -5, my right eye is -4.5 and I see 20/30 with glasses. Intacs will reduce my myopia and hence reduce my dependency on glasses without needing reading glasses. I will only need glasses for distance. I spend many hours a day on the computer and won't need glasses for this after Intacs. I am surprised Intacs isn't marketed more, many people are low to moderate myopes and could benefit from Intacs with less risks than lasik and even PRK. They would have the safety net of Intacs being removable among other advantages.
I learned about stuff such as:
Though less well known, these small implants can improve vision in patients with mild to moderate myopia without the risk of permanent eye damage inherent in the tissue removal technique of LASIK. Intacs are semi-circular disks implanted in the cornea which stretch it to assume a flatter shape. Though slightly less precise than LASIK, they are removeable and replaceable, so if the patient has an unexpected over- or under-correction, the implant can be removed and another of a different size inserted to obtain the desired correction. The implants are located at the edge of the cornea, so the central visual area is completely intact and undamaged, and the strength of the cornea is undiminished, making it a better option for pilots and those who engage in contact sports where eye injury is a possibility.
Intacs are unsuitable for severe myopia and more than minor astigmatism (1.00 diopters), as the cornea can only be stretched so far. If the Intacs are removed, vision returns to its preoperative level. Aside from vision correction, Intacs are also used to treat keratoconus. Intacs are FDA approved and 10 year studies have revealed no major problems with Intacs and very few patient complaints; however, because the procedure takes more training than LASIK, there are fewer eye surgery clinics offering it. However, the Intacs website gives a list of practitioners in each state, as well a few in Canada, Europe and Mexico.
Intacs pros over PRK
1. No cornea removed, keep all 550 microns
2. Center of cornea untouched
3. Very remote chance of overcorrection(for me)
4. Maintain prolate cornea(Allegretto can do that too)
5. Intacs can be removed, keeps future options open
6. 3x faster healing time and less pain
7. Bandage contact lens for only a day
8. Faster surgery than lasik/prk
9. 60% chance of improving BCVA(for keratoconus?)
10. No risk of ectasia, makes cornea stronger
11. Can get in one eye at a time
12. Less risk of dry eyes
13. Consistant correction, litle variation
PRK pros over Intacs
1. Avoid 35mm HG vacuum for 8 seconds
2. No foreign object in eyes
3. Can correct me to -1 instead of -2
4. $2000 cheaper(hardly matters)
5. Avoid migration complication of Intacs
On another note, if I do decide on PRK, it will be with the Allegretto wavefront guided with an 8mm prolate(not oblate!) zone to match my 8mm pupils. Wavefront-guided PRK is based on aberrometry measurements and is designed to treat both spherocylinder and higher order aberrations. I don't expect a reduction in my HOAs unless they were high to begin with, ill be getting tested for this. I do suspect I have plenty of HOAs and irregular astigmatism since my left eye corrects to 20/25-20/30 and my right eye corrects 20/40. I mentioned this 5 years ago on this forum. Ive learned alot since then but still have more to learn. It's good to be informed of all the risks.
I read that results demonstrated similar wavefront outcomes in both groups in eyes with less than 0.3 microns of pre-operative higher-order aberrations (HOAs), accounting for 83 percent of eyes. Eyes with 0.3 to 0.4 microns of pre-operative HOAs demonstrated slightly more improvement with wavefront-guided treatments than with Wavefront Optimized treatments. In cases with more than 0.4 microns of HOA, it was discovered that post-operative HOAs were reduced significantly in the wavefront-guided cohort. No symptomatic increases in aberrations were observed in either cohort. Also, the Allegretto Wave is the only standard LASIK platform that has demonstrated the ability to preserve and improve low contrast acuity.
One website claims: My 20/15 rate is about 99% in these cases."
Is this 20/15 with glasses? No way UCVA, most can't even get to 20/20 as ive learned. Besides ill be happy to just be 20/20 with glasses and surprised if I get 20/15 with glasses. How do more than very few people see such tiny letters, especially when glasses minify them even further? It would be a limitation of the retina and cone density. Well that limit may actually be 20/8 but with zero HOAs which is impossible, especially after lasik/prk. Note that I am skeptical of all exaggerated claims regarding "perfect vision" and "rare complications"
I did get a lasik consultation back in 2003 but of course did more research and decided lasik was too risky. Ive been interested in Intacs back then and still am. Because Intacs are so rarely done on myopia and very few centers even offer Intacs(mainly for keratoconus) I have been looking at PRK(not lasik) and the Allegretto is the newest, best laser in America. Nothing is risk free, I am just considering my options with the least amount of risk.
Option 1:
Reduce the -5.25 in left eye to -3.25 by setting the laser for 2d of correction. I am allowing a 1d margin because the healing response among many other factors dictate this. Thus ill end at -2.25 to -4.25 but there's a small chance I can end outside this range. Still, an overcorrection is very unlikley to occur. Allowing 3+ months for left eye to heal, then reduce the right eye from -4.75 to -3.25 by setting the laser for 1.5d of correction as well as correcting my irregular astigmatism at the same time. Allow 3+ months for right eye to heal, repeat left eye with a target of -1.5d(-0.5d to -2.5d range) post prk refraction. Allow 3+ months to heal and repeat right eye to closely match whatever left eye ultimately ends up at. Retaining -1.5d of myopia(give or take) will save some cornea, greatly reduce the risk of overcorrection and greatly reduce(not eliminate, that's impossible) my dependancy on both distance and reading glasses and allow me to use the computer with no glasses!
Should I end up better than 20/20 BCVA for some strange reason, I won't be getting an enhancement and will be happy to live with around -3d of myopia and enjoy the super sharp BCVA as well as reduced dependancy on glasses and never need reading glasses.
Should the first go of PRK on the left eye get me to -2.5 or better, an "overcorrection" to be technical, I won't repeat the left eye and just do the right eye to closely match the left eye. Ill be happy I didn't go for plano as I would have ended up significantly overcorrected for real. This would mean reading glasses or bifocals for me.
Should the results be dissatisfactory on the left eye regarding dryness, night vision, unusual outcome, complications, I won't touch the right eye. Because the difference between -3.25(therebouts) and -4.75 will be fairly close, this will minimize the aniseikonia and ill be able to go back to glasses and wait 5-10 years for better laser technology.
I would have to decide what action to take for other possible outcomes once they happen.
Option 2: Reduce the -5.25 in left eye to -3.25 by setting the laser for 2d of correction. I am allowing a 1d margin because the healing response among many other factors dictate this. Thus ill end at -2.25 to -4.25 but there's a small chance I can end outside this range. Still, an overcorrection is very unlikley to occur. Allowing 3+ months for left eye to heal, then reduce the right eye from -4.75 to -1.5(therebouts) with as little astigmatism as possible. Wait then do a second round on the left eye to closely match right eye. Will likley end up somewhere between -0.5 and -2.5 which is allowing a 1d margin from the -1.5d target. This range is acceptable in reducing my dependancy on glasses while keeping a low amount of myopia to preserve some near vision.
As to the possible outcomes that should happen, see above.
Option 3: Get both eyes done with a target of -1.5, range of -0.5 to -2.5. This is more risky for several reasons. Although it means no enhancements, there's a small chance of an overcorrection because I have no idea on the healing response. Ill be removing around 100 microns of cornea(27 per diopter for 8mm prolate zone?) so this puts me at increased risk of haze(even with MMC?) vs. removing around 50 microns each go and spreading it over 2 treatments, allowing a full healing each time. Ill be risking both eyes at once instead of one. Ill also lose the advantage of seeing thru the other eye when the treated eye is healing and vision may be slightly blurry.
Monovision is not for me, I do not want anisometropia nor risk overcorrecting the dormant distance eye, seen it happen all the time. I can't and won't aim for plano in either or both eyes for the reasons I mentioned, it's too risky and pointless to waste cornea just to trade for reading glasses. I use my eyes for near more than distance and am wearing computer glasses that correct 3.5d of my 5d of myopia. It is not realistic to expect an elimination of glasses for everything, you can choose distance, intermediate or near and wear glasses part time.
Choosing distance is the most risky because an overcorrection will result in bifocals. You can't add cornea back. Choosing intermediate to the tune of -1.5d gives me a safety margin. An "overcorrection" will likley mean ill be -0.5d instead of hyperopic. An undercorrection will mean ill be -3d and can either leave well enough alone or enhance that to around -1.5d. Choosing near is great for high myopes who just don't have enough cornea for any other choice anyway unless they want to risk IOLs. It's great to be around -2.5d instead of the -6, -7, -8(therebouts) that they are. If they don't find -2.5d acceptable and they don't want to risk IOLs, it's perfectly acceptable for them to stick with glasses like this -9d friend I know.
Thanks for reading. I am still doing research and have realistic expectations of a reduced dependancy on glasses, reducing my refractive error and understanding the risks.
edit:
1. How much cornea is removed for an 8mm optical zone? Where can I find the math?
2. I read that the cornea can't be flatter than 35d or the quality of vision goes way down. Is the flattening based on how much cornea is removed regardless of optical zone size or by how many diopters you correct?
3. Is it true the more cornea you remove, the more surface nerves that control tears get damaged? I notice lasik causes way more dry eyes than PRK, is this because the flap damages an extra 150 microns of cornea?
4. Why don't more people consider the Allegretto for PRK and to keep their corneas prolate? It's less risky and causes less damage than oblate lasik.
5. Why don't more people research something as serious as laser surgery as carefully and as long as me?
6. What kind of tests other than measuring my pupils(8mm?), dry eyes, cornea thickness(550 microns) HOAs, cornea topography should I ask for?
On March 25, I went to get a PRK consultation. I got several tests and asked more questions than anyone else. The optometrist says I probably know more about some aspects of vision than he does! First I was tested on the autorefractor which thinks im a -7 I told her it overcorrected me and she says that's common. Next I got topographies of my cornea. I knew I had irregular astigmatism from the 2005 topographies. Those also showed irregular astigmatism.
Then it was off to test my UCVA. I saw nothing on the eyechart, not even the 20/400 "E". I knew it probably would be an "E" since most eyecharts use this letter on top but I don't go by memory! I didn't think id see 20/400 being a -5 which is moderately high myopia. Throw in around -1 of astigmatism on top of the -5 myopia and you are talking 20/800 being in the ballpark. Then I tested with my computer glasses(-3.5) and saw 20/100 with them. With my distance glasses I see 20/30 in left eye and 20/60 in right eye. My right eye is a little undercorrected, it can do 20/30 BCVA.
This eyechart has 20/400, 200, 100, 80, 70, 60, 50, 40, 30, 25, 20, 15, 10 lines. Some eyecharts have additional lines such as 20/300, 20/250, 20/150, 20/120, 20/12, etc. I had asked him how rare 20/12 was and they don't have that line on their chart. Funny how 70% get 20/15, yet less than 0.1% get 20/10. Wonder what % would be in between.
My aberrometry showed a RMS of .38um in left and .55um in right. I was correct when I figured my right eye is more aberrated. My vision is not as clear in that eye. I also have more astigmatism as well. I would benefit from wavefront guided PRK since im above .3um They say my HOAs could be reduced to normal, but not eliminated alltogether which I already knew.
My pupils do measure in the 8mm range which I already knew. I was surprised that they give everyone the same 6.5mm optical zone with a blend to 9.2mm. This will take 16um/diopter. They say they can correct astigmatism together with myopia no problem. Even my low astigmatism can be corrected(rather, reduced) with a best fit oval ablation profile. I asked about the 8mm optical zone and he says they don't do this as it "eats" too much cornea and there's no room for a blend zone (it would be 12mm) if an 8mm optical zone were to be used. Also a blend zone is important for a smooth transition and it's better than a larger optical zone with no room for any blend zone. He says 1 in 25 people have pupils my size. There's only been one case of poor night vision under the allgretto laser with unknown cause.
He says I can aim for a -1 or -1.5 or anything I feel like. This will greatly reduce the risk of an overcorrection to hyperopia. Ill also save several microns of cornea. I said 350 microns was the safe minimum and he said I am absolutely correct. Get too thin and you get ectasia. Ill have to wear a thin pair of distance glasses for TV and driving but I get to see clearly without reading glasses for everything. I have the accomodation of a 40-45 year old and wear -3.5s for the computer and -5s for distance. Ill probably go for -1 and regress slowly over the years. Ill become more myopic as I get older, said my optometrist. No problem, ill need more myopia as my presbyopia worsens to preserve my near vision and stay out of reading glasses. I spend 75% of my time wearing my -3.5 glasses and only 25% wearing my -5 glasses so this makes sense.
They had a near chart and I was seeing 20/40 with my -5 distance glasses and 20/25 with my -3.5 computer glasses. This is from 16 inches. I have to take my glasses off and look from 8 inches to see the tiny 20/20 line. I can live with 20/25 near vision. I don't get 20/20 distance vision either as the 20/20 line is far too tiny. He says some people see better after lasik/prk than they do with their glasses. I said glasses minify and distort and he says im correct. They may see 20/25 with glasses and get 20/20 after the surgery. If they see 20/20 with glasses, they could be 20/15 after surgery!
He says there's a 97% chance of 20/20, 70% chance of 20/15 and less than 0.1% chance of 20/10! Of the 16,000+ laser surgeries performed only 4 people have ever attained a 20/10 UCVA! I said I read on the internet that 1 in 500 see 20/10 and he said try 1 in 5000! He explained that you need a superb retina and absolutely no refractive error. The exception is a small amount of hyperopia that can be accomodated by a young, non presbyopic eye. The retina limits most people to 20/15 or 20/20, but not everyone's retina will be capable of 20/20, if so, they won't be 20/20 after surgery, not even with glasses.
He says you can be 20/20 with -0.25 but he's never seen a -0.5 attain 20/20 without glasses. No one with 20/20 UCVA can be -0.5, anyone who says so is wrong and measured it wrong. He went on to say that -1 gives you 20/40 to 20/50 and -1.5 gives 20/60 to 20/80 in most of the patients he's refracted. Would be interesting to learn more about the correlation between diopters and 20/xx.
I had thought the chance was 10% of getting to plano and 67% chance of give/take half diopter and 90% chance of give/take one diopter and he says that's wrong, the odds are very, very good of 20/20 UCVA after surgery. He says young people are deliberately overcorrected to +0.25 to account for regression in the future. Also those with a spherical equivalent of plano or a quarter diopter can still see 20/20.
My corneal thickness was measured at 570 and 563, no problem for PRK nor lasik for the matter. I am choosing PRK because the risks are less. I know there's a long healing period and I read lasik is more popular because people want near instant gratification. He said im correct and also explained ill need to wear bandage contact lens for 3-5 days and expect 4-8 week healing period. I am fine with this. When I asked if I should get one eye done at a time, he said they won't be in balance and that the risk is the same for getting one or both eyes done. Guess ill get both eyes done at the same time and aim for a -1 sphere, 0 cylindar and ill end up somewhere in that ballpark.
I will be doing more research and asking more questions. The surgeon has my medical records and will be reviewing it and letting me know the best options and risks once he returns from vacation. I heard I was a candidate but I still want to learn more even though I know plenty. I also need other opinions from other laser centers.
I got a PRK candidacy test at another center:
First, I filled out a lasik checklist. A few of the questions stood out and I am reposting them here as it's informative. Q: Would you be satisfied if your natural vision was greatly improved even if you still had to wear corrective lenses some of the time? A: Yes. Q: Do you feel that good vision without glasses is more important than perfect vision with glasses? A: Yes. Q: Is it acceptable to you that you may need glasses for reading after lasik? A: No.
They are pointing out that lasik(or PRK) can reduce your dependancy on glasses. I expect my natural(UCVA) vision to be greatly improved, which should be easy since im about 20/800! I don't have perfect 20/20 vision with glasses anyway and besides, presbyopes can *not* have perfect vision, they must choose to either see well at distance or at near. If they want both, progressive glasses would be the way to go. Because I can see clear from near, why should I give that up? I am aiming for a -1.5 target so I greatly improve my distance vision while still keeping most of my near vision. Ill be able to see the computer and regular size print without readers. I already wear computer glasses most of the time and only switch to distance glasses when I get out of the house.
The usual battery of tests were done on me, same as the first PRK center. This wavefront test(6.5mm diameter) says I have a half micron of HOAs. It also says I have almost -6d of spherical equivalent. I am more like a -5.5 though. I also got an orbscan that shows the color contours and estimated my cornea at ~550 which is average thickness.
I asked lots of questions and the doctors were impressed with how knowlegeable I am. A female optometrist measured my pupils at between 8mm and 9mm. She gave me a nearvision card and I could read line 5(20/50?) with glasses and without them, I could easily see the smallest line from about 8 inches. She is 43 and presbyopic herself but thanks to being -0.75, she does not yet need reading glasses(her friends are so jealous!) and only needs "cheaters" for night driving. I figured her UCVA was 20/30 and was correct. Her BCVA is an amazing 20/15!
My BCVA is 20/25 to 20/30, the 20/20 line is simply too small because my glasses minify. If you can still see 20/20 with eyes as bad as mine, you have an amazing retina! She did say that I would be surprised by how some people can actually see better than 20/20. I certainly am surprised! The 20/20 line is tiny, just a third of an inch! With my glasses, it's much smaller than that!
I got to meet the surgeon and he was also impressed by how much I knew. He discussed monovision but it's not for me due to anisometropia. I mentioned that I am aiming for a slight undercorrection of -1.5 to preserve some of my near vision and will accept the occasional need for distance glasses. I don't drive and spend alot of time on the computer. He says the laser is accurate to 0.12 diopters and most people end within 0.25 diopters. Get me in the ballpark of -1.5 give or take half diopter and ill be happy. He says I have realistic expectations and am almost certain to achieve that. There's always the option for an enhancement. Ill probably leave well enough alone unless I end up hyperopic or very undercorrected like a -3.
Speaking of expectations, he says alot of people have high expectations and they insist on "perfect" vision. I said they are being unrealistic. If they are presbyopic, they will never be free of glasses and will never see clearly both distance and near. Monovision lets you see clear but with only one eye at a time which isn't for me. I also asked if you reject those who demand "perfect" vision and he laughed and gestured with his foot "I kick them out like this" and swung his leg. My dad later told me he was joking. I told dad that unhappy patients are bad for business because they warn their friends away.
We discussed the fear of overcorrections and he said it's rare to be overcorrected or end up with a large undercorrection. His nomogram actually programs the laser for +0.25 or even +0.5 overcorrection for young people and an undercorrection by the same amount for old people. He will program the laser so ill initally be -1 sphere then ill heal to -1.5. I said even if I end at -1, that's fine with me. There's a 1.5 diopter "buffer" before I end up hyperopic, something that would result in bifocals for presbyopes or rolling the die again on an enhancement. End up slightly undercorrected and no problem, you get to see clear from near and only need glasses for stuff like driving, watching movies and seeing things from a mile away.
We also discussed the fact the Allegretto laser is the only laser that is capable of a prolate profile. This is important for preserving quality of vision and giving the best possible night vision. An oblate ablation results in poorer quality of vision. Also this laser has a blend/transition zone to 9.2mm which results in less of a decrease in night vision compared to older lasers with a small ablation zone and no transition zone. Due to my huge pupils, I expect some decrease in night vision netherless. Ill probably be seeing some halos in the transition zone area. Another reason "perfectionists" should stick with glasses.
He asked if I wore contacts which I replied that I tried them about 20 times and they caused discomfort, irritation, dryness and felt like an eyelash. That's why im considering PRK to improve my vision and be less dependant on glasses. A note to you contact lens wearers, stick with contact lens. They do the job better than laser surgery for less cost and risk. You will be able to see without distance glasses by wearing contact lenses.
He will remove my epithelium with alcohol and a scalpel/brush. He used to do LASEK but it was no better than PRK. 80% of his surgeries he performs are LASIK and 20% are PRK. I correctly said that's because people want near instant gratification and heal in days, not weeks. PRK has less risks and gives better long term results. In exchange, I will endure wearing uncomfortable bandage contacts for 5 days, then deal with fluctuating vision for a few weeks before I fully heal and my vision stabalizes around a -1.5
Wavefront optimized vs. guided was discussed and he says wavefront guided can reduce my HOAs from 0.5um to 0.4um while wavefront optimized may increase them by 0.1 or 0.2 but that I won't notice a difference, especially since ill have -1.5d of blur anyway. He recommends wavefront guided if your HOAs are 0.8um or higher. His laser only does wavefront optimized so youd need to get it done in a different center. I will have to research this more, but I would prefer wavefront guided for myself if I can find a nearby center. It would give me a better chance of preserving more of my night vision.
Thanks for reading my long post regarding what went on during my PRK evaluation. What else should I know of? Anything you wish to share yourself?
Update(Dec 29, 2010) I haven't gotten around to this in a while but at this point im going to wait for Keraflex as well as better lasers(such as the IVIS) to come to a location near me. The PRK center with the custom wavefront Allegretto rejected me as a candidate because I knew too much and asked too many questions! Oh well, their loss as I might have gone ahead back then. The other center also has the Allegretto laser but they don't offer custom wavefront. No thanks, I don't want an increase in HOAs.
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