Low myopia and high astigmatism, what to expect ?

If you are thinking about having Lasik, IntraLasik, PRK, LASEK, Epi-Lasik, RLE, or P-IOL eye surgery, this is the forum to research your concerns or ask your questions.

Low myopia and high astigmatism, what to expect ?

Postby ikho » Thu Oct 01, 2009 6:59 am

Hi there,

First of all, I have to thank a lot the organisation for the helpful articles and for the forum. I spent quite a long time looking for objective and complete informations. Between the advertisements and the scary websites made by the unhappy patients, this website is one of the rare place to get unbiased informations. More, I found explanations to some of the facts usually given without any other informations.

Well, here is my prescription from the oct. 8th 08 made for eye glasses :
OD sph. pl cyl. -1.75 x 175
OS sph. pl cyl. -1.00 x 175

here is the prescription from march 31st 09 made for contacts :
OD sph. -0.50 cyl. -2.25 x 180
OS sph. -0.25 cyl. -1.25 x 180

I'm 32.
I just got my commercial helicopter pilot licence ( rotary wings don't fly at 30,000 feet as liners do ).
I haven't worn any eye glasses before being 29 and I wore them only to drive and read. Since the beginning of the year ( and my pilot medical certification ) I have to wear it every time.
I spent 5 months in trying a large number of contacts ( soft and RGP ) without success.

For the prescription, I feel quite confused. It seems it's changing, but I don't really rely in the accuracy of the measures. I don't think it's possible that my astigmatism changed its axis for example ( but I'm not an expert ). Actually, a couple of month ago I had a pre-op exam and one told me that my prescription is not really changing, and that will be ok to have a surgery. Well, I still want to check how would be the prescription today.

Ok, now my questions :
1- I wonder if the half sphere rule apply for my left eye. By the way, I've never read about that rule until I found that website and no surgeon told me about that issue. Are they all supposed to know it ?

2- Even without the issue of the half sphere rule, my right eye has a quite high astigmatism since it's above the 2D. Again, I've never heard that astigmatism was so much more challenging than mypia. I found there a way to compute our risk factor but the result doesn't tell that my case is risky. So, I'd like to know more about the difficulties involved for my astigmatism.
More, it seems that I don't have enough myopia to fully correct the astigmatism level because of the coupling effect ( correcting each diopter of astigmatism automatically corrects between 0.25 and 0.33 diopter of myopia ). What to expect in that case ? Is it possible to correct the people with hyperopia and astigmatism ?
I read many times that one should expect to have more than one surgery to fine tune an hight level of astigmatism. The surgeon I saw said "probability of needing an enhancement between 5% and 10%. How to deal with an enhancement if there is not enough myopia left ?

3- The first surgeon I've seen told me my odds of not having to wear glasses anymore were 99%. Seems to be contradictory with the challenge of the astigmatism, isn't it ?

4- The wavefront guided ablation is supposed to be safer to avoid HOA troubles ( and more efficient to get a high visual accuracy ). Here I read that with such a small amount of myopia a conventional topography-guided ablation may be best. Why ? Because of the risk of being overcorrected and becoming farsighted ? I had a wavefront diagnostic and no one told me about a natural already elevated HOA I could have. But I'm still very concerned about the HOA issue as I could lose the right to fly if I experience troubles in night vision or loss of contrast.

5- I'm from France and I'd definitely wanna meet a french speaking surgeon to be able to feel him/her and build a trust relationship ( the prices are quite similar in Canada and France ). In that website, they advice having lasik instead of surface ablation when astigmatism is over 2D. Before reading usaeyes.org I already was worrying about the lasik flap long term consequences ( especially the dry eye syndrom ). What do you think is the best option ? Do you agree with having lasik more than surface ablation when having a high astigmatism ?

6- I don't easily find eye center advertising about the lasek technique in Canada ( where I live now ). Does the surgeons offering prk usually do lasek too ?

7- The one who are over the age of 40 should think about keeping an amount of myopia and/or having a monovision. Despite the fact I can afford losing depth vision, why the one under 40 aren't concerned ? I'll also have presbopia after a while.

Thanks for reading me until there.
Thanks for participating in that well done forum.
ikho
 
Posts: 5
Joined: Thu Oct 01, 2009 12:36 am

Re: Low myopia and high astigmatism, what to expect ?

Postby ikho » Tue Oct 13, 2009 5:34 am

@LasikExpert
I wished you would take the time to answer some of my questions.
Is it possible to get your opinion too ?

thanks
ikho
 
Posts: 5
Joined: Thu Oct 01, 2009 12:36 am

Re: Low myopia and high astigmatism, what to expect ?

Postby ikho » Thu Oct 15, 2009 7:28 pm

why the post of Anyman has been removed ?
ikho
 
Posts: 5
Joined: Thu Oct 01, 2009 12:36 am

Re: Low myopia and high astigmatism, what to expect ?

Postby LasikExpert » Thu Oct 29, 2009 5:03 pm

ikho wrote:why the post of Anyman has been removed ?


The purpose of this forum is to promote the exchange of patient-oriented information regarding Lasik and similar refractive surgery techniques that will assist a patient understand and hopefully resolve medically related concerns. Comments that do not focus on this purpose are subject to removal.
Glenn Hagele
Volunteer Executive Director
USAEyes

Lasik Info &
Lasik Doctor Certification

I am not a doctor.
LasikExpert
Site Admin
 
Posts: 3309
Joined: Fri May 12, 2006 6:43 am
Location: California

Re: Low myopia and high astigmatism, what to expect ?

Postby LasikExpert » Thu Oct 29, 2009 6:51 pm

ikho wrote:1- I wonder if the half sphere rule apply for my left eye. By the way, I've never read about that rule until I found that website and no surgeon told me about that issue. Are they all supposed to know it ?


The Lasik laser coupling effect is a consequence of the physics of corneal reshaping and applies to PRK, Lasik, Epi-Lasik, All-Laser Lasik, and LASEK. For each 1.00 diopter of astigmatic correction there is an automatic myopic (nearsighted, shortsighted) correction of 0.25 to 0.50 diopters, depending upon the laser technology used. If you don't have any myopia to correct, the surgery will induce hyperopia (farsighted, longsighted) vision.

Surgeons who understand this dynamic may adjust the treatment plan so the coupling effect is minimized, however the ability to fully resolve laser coupling is limited. It is sometimes necessary to combine a hyperopic correction into the treatment plan to counter the coupling effect.

You have a significant amount of astigmatism (cylinder) with virtually no myopia (sphere), therefor the coupling effect will be an important factor in any laser vision correction technique you consider.

ikho wrote:2- Even without the issue of the half sphere rule, my right eye has a quite high astigmatism since it's above the 2D. Again, I've never heard that astigmatism was so much more challenging than mypia.


Astigmatism means that the cornea is not spherical like the top of a ball, but is elliptical like the back of a spoon. The "tip of the spoon" is the astigmatism, which focuses light off-center and can contribute to poor vision quality and even doubled images. Reshaping the cornea to eliminate or reduce the tip of the spoon is more challenging, as we describe in our article on Lasik and astigmatism correction.


ikho wrote:More, it seems that I don't have enough myopia to fully correct the astigmatism level because of the coupling effect ( correcting each diopter of astigmatism automatically corrects between 0.25 and 0.33 diopter of myopia ). What to expect in that case?


It would be reasonable to expect a hyperopic shift that would leave you with about 0.50 to 1.00 diopter of hyperopia. Although the number may sound small, hyperopia has a much greater effect on vision quality than myopia, especially for people who are also presbyopic.

Presbyopia is when the natural lens of the eye is less able to change shape and thereby focus on near objects. When at rest, the human eye is focused for distance - about 20 feet (6 meters) and beyond to infinity. To see objects closer, it is necessary for the lens to change shape. This is called accommodation. Presbyopia starts at around age 8-10, but is not normally noticeable until after about age 40 when seeing near objects becomes more and more difficult. Most people use reading glasses or bifocals to be able to see near objects when presbyopia becomes problematic.

At age 32 you probably have excellent accommodation. This is good for you, but presents an important consideration. It is possible that your eyes will "focus around" 0.50 to 1.00 diopters of hyperopia. In essence, your eyes will always be in a state of accommodation if vision correction surgery makes you hyperopic. While this will likely provide you good vision at distance and near, it may also cause eye strain that presents as headaches, vision fluctuation, even nausea and vertigo. Even if you do not suffer any side effects from accommodating around induced hyperopia now, you most certainly will suffer the effects of hyperopia in about ten years when you start to become more presbyopic. The combination of presbyopia and hyperopia commonly presents poor quality vision at all distances.

You may be able to focus around the hyperopia for years with no problem if you elect to have laser vision correction surgery now and end up with induced hyperopia. At some point, however, that hyperopia will become an important issue in vision quality.

Your doctor can measure any induced hyperopia by paralyzing the natural lens within the eye and halting accommodation. This is called a cycloplegic refraction (which is better, one or two, with eyes dilated) and will be an important evaluation after laser vision correction for astigmatism.

ikho wrote:Is it possible to correct the people with hyperopia and astigmatism ?


Yes, however hyperopic correction is more challenging that myopic correction.

ikho wrote:I read many times that one should expect to have more than one surgery to fine tune an hight level of astigmatism. The surgeon I saw said "probability of needing an enhancement between 5% and 10%. How to deal with an enhancement if there is not enough myopia left ?


You are well advised to expect enhancement surgery to fully correct your high level of astigmatism. What would probably be planned would be straight-forward astigmatic correction to resolve as much of the astigmatism as possible even if it induces a bit of hyperopia, and then the enhancement surgery would be a hyperopic and astigmatic correction to resolve residual astigmatism and induced hyperopia.

ikho wrote:3- The first surgeon I've seen told me my odds of not having to wear glasses anymore were 99%. Seems to be contradictory with the challenge of the astigmatism, isn't it ?


The odds you will need glasses at some point in the future is 100%. When presbyopia hits, you will need glasses to see near objects. That may be ten years away, but do not expect to be glasses-free for the remainder of your days.

Although the challenge of high astigmatism correction is significant, with proper planning vision correction surgery may be quite successful. What you need to understand is that yours will not be the "20-Minute Miracle". You will likely need at least two surgeries and your vision after surgery without glasses may not be as good as vision before surgery with glasses. Your vision after surgery may be very good and completely acceptable, but for perfect vision you may still need glasses or contacts. The question is if being able to function most of the time without glasses is an adequate outcome. You may get a "perfect" outcome - it is quite possible - but it would be wise to be prepared for less than perfection and still needing glasses on occasion.

ikho wrote:4- The wavefront guided ablation is supposed to be safer to avoid HOA troubles ( and more efficient to get a high visual accuracy ). Here I read that with such a small amount of myopia a conventional topography-guided ablation may be best. Why ?


Because astigmatism is all about topography. Astigmatism is a "bump" on the cornea. In your case, it is a very high bump. Topography-guided surgery may resolve the astigmatism better than wavefront-guided because virtually all of your problem is astigmatism. A wavefront-guided enhancement surgery after a topography-guided initial surgery would likely be an excellent combination.

ikho wrote:I had a wavefront diagnostic and no one told me about a natural already elevated HOA I could have.


As a general rule, all laser vision correction will increase higher order aberrations (HOA). As a general rule, wavefront-guided surgery induces less HOAs than conventional (including topography-guided) laser ablations. Whether or not the HOA elevation will actually interfere with vision will depend in large part on where your HOAs are now. If they are moderately low, then a slight increase may not be an issue. Although HOAs tend to increase with surgery, HOAs can also be decreased through wavefront-guided surgery. This does occur, but it would be unreasonable to expect a reduction in normal range HOAs after surgery.

ikho wrote:But I'm still very concerned about the HOA issue...


HOAs are a measuring device, not a cause. HOAs are caused by imperfections in the optics of the entire vision optic system, including cornea, aqueous, lens, and vitreous. Inducing an imperfection in any one of these elements can raise HOAs. Although modern laser vision correction surgery is amazingly accurate, it is not perfect and as a general rule induces imperfections. What is important is if these imperfections interfere with vision. If your current HOAs are moderately low, a small increase that would normally be associated with laser vision correction surgery may not actually affect vision quality. Human optics are far from perfect, and yet we see rather well despite the imperfections.

ikho wrote:... as I could lose the right to fly...


PRK and All-Laser Lasik is currently approved for US military aviators, even US Navy Top Gun pilots. That does not mean vision correction surgery is right for you, but it can be.

ikho wrote:...if I experience troubles in night vision or loss of contrast.


You will want to read our article about Lasik and pupil size concerns. You need to discuss in detail your current HOA and contrast sensitivity to determine if the reasonably expected increase in imperfections would likely push you over the threshold and into poor vision quality in low light environments.

ikho wrote:5- I'm from France and I'd definitely wanna meet a french speaking surgeon to be able to feel him/her and build a trust relationship ( the prices are quite similar in Canada and France ). In that website, they advice having lasik instead of surface ablation when astigmatism is over 2D. Before reading usaeyes.org I already was worrying about the lasik flap long term consequences ( especially the dry eye syndrom ). What do you think is the best option ? Do you agree with having lasik more than surface ablation when having a high astigmatism ?


I do not. I have a very strong personal bias toward surface ablation techniques like PRK, LASEK, and Epi-Lasik.

A: The probability of a Lasik flap complication is quite low, but no flap means no possibility of a Lasik flap complication during surgery or at any time during the patient's life. Remember, once you have had Lasik you have always had Lasik. In most cases, no possibility of a complication is better than a low probability of a complication.

B: A healthy cornea will remain stable so long as at least 250 microns of the cornea remains untouched - more untouched cornea is always better. The Lasik flap will require the laser ablation to be 90-160 microns deeper into the cornea. A surface ablation technique will give the cornea this extra 90-160 microns of stability, whether it is required or not.

C: Modern lasers are able to create very nuanced sculpting of the cornea. Laying a flap on top of that nuanced sculpting will mute the effect. It is like putting a comforter on top of wrinkled sheets. You don't get the effect of the wrinkles. That may be fine on a bed, but is the opposite of what you want in vision correction surgery. A surface ablation technique will realize the greatest advantage of the modern laser ablation mapping.

D: You will undoubtedly need enhancement surgery. Either the flap will be lifted or the enhancement surgery will be PRK on the Lasik flap. A flap lift increases the probability of epithelial ingrowth. Epi-Ingrowth is a problem that can be resolved, but it is a problem. If you will need PRK for the enhancement anyway, just do PRK first and second.

E: Primary advantages of Lasik are a fast visual recovery and virtually no pain. PRK, LASEK, and Epi-Lasik are going to be less comfortable and will take some time for full vision recovery. You will not be seeing much for 1-3 days, will have "functional fuzzy" vision for 1-3 weeks, and it won't be until about a month to 8 weeks after surgery before you get the crispness you seek. If you can deal with the delayed vision recovery and don't mind taking the pain meds, then surface ablation may be an acceptable alternative.

F: Many doctors don't like PRK because PRK patients require more "chair time". Because your vision recovery is slower and there is more discomfort, you are not a happy camper for a while and you don't get anything near the "20-Minute Miracle". Like patients, doctors prefer instant vision recovery and no pain. What is good for marketing Lasik may not be the best for your particular surgery plan.

ikho wrote:6- I don't easily find eye center advertising about the lasek technique in Canada ( where I live now ). Does the surgeons offering prk usually do lasek too ?


To answer your direct question, virtually and surgeon who does PRK can do LASEK, but for many reasons may not elect to recommend LASEK.

The difference between PRK and LASEK or its cousin Epi-Lasik is how the epithelium is handled. Epithelial cells are the fastest reproducing cells in the human body, but it does take time for them to cover the treatment area, thicken, and smooth. In PRK, the epithelium is removed and this will cause a full wound response: you will have one angry eye. Although this can be managed with meds, both vision recovery and discomfort are issues with PRK.

LASEK mortally wounds the epithelium, but the cells are repositioned over the treatment area. Think of this as a natural bandage. The theory behind LASEK is that since the epithelium is still there (although the cells are dead or dying), the wound response is muted. Studies have been mixed on this and several prominent surgeons have publicly considered LASEK and Epi-Lasik to be so much expensive luggage that does not really have much, if any, positive effect. Final vision recovery can actually be delayed a bit because LASEK and Epi-Lasik require the eye to slough off the dead cells and replace them bit by bit, whereas in PRK the entire area is subject to immediate new cell growth.

ikho wrote:7- The one who are over the age of 40 should think about keeping an amount of myopia and/or having a monovision. Despite the fact I can afford losing depth vision, why the one under 40 aren't concerned ? I'll also have presbopia after a while.


There are two ways to describe myopia. One is that you cannot see distant objects very well. The other is that you can see near objects well. Reading glasses induce myopia to bring near objects into focus. If the majority of your daily life revolves around near vision, then being a bit myopic after presbyopia has set in can be advantageous. Monovision is a technique to have the non-dominant eye myopic for near vision and the dominant eye fully corrected for distance vision. For many people, the brain can combine the two images for acceptable near and distance vision, although not everyone can tolerate monovision's effect.

Monovision and residual myopia are not advantageous until presbyopia has reduced the ability to see near objects because accommodation allows the young adult to see near objects.
Glenn Hagele
Volunteer Executive Director
USAEyes

Lasik Info &
Lasik Doctor Certification

I am not a doctor.
LasikExpert
Site Admin
 
Posts: 3309
Joined: Fri May 12, 2006 6:43 am
Location: California


Return to Thinking About It

Who is online

Users browsing this forum: Yahoo [Bot] and 1 guest

cron