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.

2. Dry eyes

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. Presbyopia

Green 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.

7. Acceptable range

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?


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.


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!

10. Desires

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.


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.


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


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