Higher Order Aberrations

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Higher Order Aberrations

Postby richbron » Sun May 27, 2007 7:05 pm

What is the "normal" range of HOA?

Are high prescription Lasik treatments more prone to HOA?

What treatments are available for HOA - what is the success??

Is there danger that the above treatment can further increase HOA??

Thanks
Richard
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Postby LasikExpert » Mon May 28, 2007 3:27 am

Different aberrometers generate slightly different numbers, but a root mean squared (RMS) of higher order aberrations (HOA) of about .35 is around the norm. Keep in mind that this is an RMS and if one particular aberration is very high the RMS may be within the norm but the patient have symptomatic vision. You can't just look at one number and get the whole picture.

All cornea-based laser surgery (Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik) tend to induce HOA. Conventional ablation tends to induce more HOA than wavefront-guided ablation. Some HOA may be reduced, but it depends upon the exact nature of the HOA. Again, one number does not tell the story.

No laser has been approved to treat HOA and HOA are only a measurement of a problem caused by something else. A yard stick does not cause three feet of yarn, but it can accurately measure the yarn. HOA is a yardstick.

You may want to read our article about custom Lasik for more details.
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HOA

Postby richbron » Mon May 28, 2007 1:04 pm

Thanks Glenn.

I underwent Lasik in Nov 2005 (pre-op astigmatism of -5.75). My post lasik astigmatism is in the region of -0.75 in R and -1.0 in Left. The vision in my left eye is extremely poor and I am still totally reliant on glasses (my other refraction is plano - ie astigmatism is the only issue I have).

My glasses, particularly the right eye, do not fully correct and since Lasik have terrible night vision (starbursts etc etc).

At my request my Lasik Dr performed a wavefront topography - my Left eye was 0.3 and right 0.9 HOA. The doctor was quick to point out that this should not have any bearing on my quality of vision and suggested that I have forgotten the quaility of vision I experienced pre lasik (load of BS).

What options are available to me?
Is it possible that I could have wavefront guided lasik to address the residual astigmatism and address the HOA or do I risk increasing the HOA even further?

Are there glasses/contact lenses designed to correct HOA?

I am currently living in South Africa but would consider travelling to see an expert anywhere in the World.

Thanks for your help
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Postby LasikExpert » Mon May 28, 2007 4:33 pm

Remember that HOA is the yardstick, not the cause. The cause of your poor night vision is undoubtedly largely due to the extreme initial astigmatism and an issue of ablation size.

You need to fully understand our article about Lasik night vision problemsfor the remainder of my information to make sense.

Astigmatism is when the top of the cornea is not spherical like the top of a ball, but is elliptical like the back of a spoon. The astigmatism is the "tip" of the spoon.

The treatment area when correcting myopia (nearsighted, shortsighted) vision is round. If the laser is set for a 6.5mm ablation zone, the treatment will be 6.5mm x 6.5mm.

To treat astigmatism, the ablation area is elliptical. It is made elliptical by narrowing two sides of the ablation zone. The size of the ablation zone to treat your astigmatism was probably about 5.mm x 6.5mm. It is even possible that due to your very high astigmatism the narrow width was even smaller.

This means that a portion of your correction the treatment zone was 5.0mm across. If your pupils naturally dilate to the average of 6.5mm, then you would have about 1.5mm of differently corrected cornea - probably undercorrected - at the outer edges of the narrow width of the astigmatic ablation zone.

What you would probably have is a crescent of undercorrected cornea on both sides of the perpendicular axis of your original astigmatism. It is likely that your night vision effects are uneven. As an example, the spikes on two sides of a starburst would be longer and the angle stays the same.

The fact that your glasses do not fully correct would indicate that your ablation is uneven. It may be that the correction of the astigmatism created smaller but irregular astigmatism. By reducing the one big "tip" of the spoon, the surgery made smaller little tips. This irregular astigmatism is very difficult to correct with glasses.

The wavefront aberratometer does create a valuable map of the vision abnormalities. It also can indicate the probability of correcting the cause of your difficulties. The reported 0.90 HOA would be a root mean squared (RMS). Think of it as an average of all the HOA. Some are going to be much higher and some will be much lower. Knowing the value of each HOA as presented in Zernike polynomials will provide a much greater understanding of the cause of your vision difficulties and the probability of correction. I suspect that you have very high coma and secondary astigmatism. It is difficult to resolve the causes of both of these aberrations, but not impossible.

There are a couple of things that you can do immediately that may help you. One is to ask your doctor if Alphagan P would be appropriate. This is a glaucoma eye drop medication that has the side effect of reducing pupil size. If your pupils do not get large enough for light passing through the aberrated portion of the cornea to get inside the eye and be "seen", then you will not suffer the nighttime vision effects.

You should also investigate rigid gas permeable (RGP) contact lenses. RGPs can "squish down" some of the surface irregularities to provide better vision than you would get with spectacles.

There is a company that creates wavefront-optimized glasses, however dure to the nature of the likely causes of your vision problems it does not seem likely that glasses will be very helpful.

Please contact me directly at glenn dot hagele at usaeyes dot org and I will research a surgeon for you to consider for additional treatment.
Last edited by LasikExpert on Tue May 29, 2007 4:21 pm, edited 1 time in total.
Glenn Hagele
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Postby richbron » Tue May 29, 2007 1:34 pm

Hi Glenn

Thanks for your very informative mail.

I must state though that my uncorrected vision is extremely poor (particularly my right eye which has the small prescription). To give you an example, I struggle to read a computer without glasses and whilst driving cannot read the car number plate of the car directly in front. With such a small astigmatism (-0.75 R and -1.0 L) it makes me think that main cause of my vision quality is not the astigmatism.

I have struggled for 18 months to convice my Doctor that I am wearing glasses (even though they do not fully correct) out of necessity and NOT comfort. He told me hismelf that his astigmatism is the same as mine and he has NEVER worn glasses.

I am going to another Doctor later this week where I will request an independent topography.

I cannot stress enough how poor the vision is in my right eye.

Thanks
Richard


LasikExpert wrote:Remember that HOA is the yardstick, not the cause. The cause of your poor night vision is undoubtedly largely due to the extreme residual astigmatism and an issue of ablation size.

You need to fully understand our article about Lasik night vision problemsfor the remainder of my information to make sense.

Astigmatism is when the top of the cornea is not spherical like the top of a ball, but is elliptical like the back of a spoon. The astigmatism is the "tip" of the spoon.

The treatment area when correcting myopia (nearsighted, shortsighted) vision is round. If the laser is set for a 6.5mm ablation zone, the treatment will be 6.5mm x 6.5mm.

To treat astigmatism, the ablation area is elliptical. It is made elliptical by narrowing two sides of the ablation zone. The size of the ablation zone to treat your astigmatism was probably about 5.mm x 6.5mm. It is even possible that due to your very high astigmatism the narrow width was even smaller.

This means that a portion of your correction the treatment zone was 5.0mm across. If your pupils naturally dilate to the average of 6.5mm, then you would have about 1.5mm of differently corrected cornea - probably undercorrected - at the outer edges of the narrow width of the astigmatic ablation zone.

What you would probably have is a crescent of undercorrected cornea on both sides of the perpendicular axis of your original astigmatism. It is likely that your night vision effects are uneven. As an example, the spikes on two sides of a starburst would be longer and the angle stays the same.

The fact that your glasses do not fully correct would indicate that your ablation is uneven. It may be that the correction of the astigmatism created smaller but irregular astigmatism. By reducing the one big "tip" of the spoon, the surgery made smaller little tips. This irregular astigmatism is very difficult to correct with glasses.

The wavefront aberratometer does create a valuable map of the vision abnormalities. It also can indicate the probability of correcting the cause of your difficulties. The reported 0.90 HOA would be a root mean squared (RMS). Think of it as an average of all the HOA. Some are going to be much higher and some will be much lower. Knowing the value of each HOA as presented in Zernike polynomials will provide a much greater understanding of the cause of your vision difficulties and the probability of correction. I suspect that you have very high coma and secondary astigmatism. It is difficult to resolve the causes of both of these aberrations, but not impossible.

There are a couple of things that you can do immediately that may help you. One is to ask your doctor if Alphagan P would be appropriate. This is a glaucoma eye drop medication that has the side effect of reducing pupil size. If your pupils do not get large enough for light passing through the aberrated portion of the cornea to get inside the eye and be "seen", then you will not suffer the nighttime vision effects.

You should also investigate rigid gas permeable (RGP) contact lenses. RGPs can "squish down" some of the surface irregularities to provide better vision than you would get with spectacles.

There is a company that creates wavefront-optimized glasses, however dure to the nature of the likely causes of your vision problems it does not seem likely that glasses will be very helpful.

Please contact me directly at glenn dot hagele at usaeyes dot org and I will research a surgeon for you to consider for additional treatment.
richbron
 
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Joined: Tue Jan 23, 2007 4:20 pm

Postby DryEye » Tue May 29, 2007 2:03 pm

Can HOA's cause other visual disturbances other than starbursts, ghosts, etc.?
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Postby LasikExpert » Tue May 29, 2007 3:56 pm

HOAs don't cause anything. They are a measurement system of optic aberrations. Optic aberrations can cause visual effects other than starbursts and halos.
Glenn Hagele
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Postby DryEye » Tue May 29, 2007 3:59 pm

So, post surgery if one has visual disturbances that can't be chalked up to LOA's and weren't there before surgery than HOA's are the culprit?
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Postby LasikExpert » Tue May 29, 2007 4:35 pm

Lower Order Aberrations (LOA) are the optic aberrations that are able to be resolved with sphere and cylinder correction - in other words LOA are corrected with glasses. HOA are caused by optic aberrations that are generally not able to be corrected with glasses.
Glenn Hagele
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USAEyes

Lasik Info &
Lasik Doctor Certification

I am not a doctor.
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Postby DryEye » Wed May 30, 2007 2:33 pm

Is there a rule of thumb on HOA's for enhancements? Does lifting the flap induce them again or more of them? Does PRK over a flap have a better chance of not creating them?
Thanks!
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Postby LasikExpert » Wed May 30, 2007 7:11 pm

Depending upon the situation, PRK on the Lasik flap may be more likely to provide a better outcome because there is no manipulation of the already healed flap.
Glenn Hagele
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USAEyes

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Lasik Doctor Certification

I am not a doctor.
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Z Wave Contact Lenses

Postby richbron » Mon Jul 09, 2007 9:21 am

I have recently come across the Z Wave contact lens - contact lens unique to your cornea used to address Higher Order Aberrations. A wavefront is used to design the back of the lens so in theory the fit should be extremely comfortable.

Has anybody tried these lenses; if so does it improve night vision and general HOA effected quality of vision, how did you find the comfort.

I am meeting with my Lasik Doc in 2 weeks time but will not condsider further treatment. Because of Lasik my HOAs have escalated and I do not feel comfortable undergoing further treatment to correct this (I must be mad to think otherwise).

I reside in South Africa and would most likely have to consider travelling abroad (eg Dr Maller in Ft Lauderdale) to be fitted - Glenn are you aware of any practioners in South Africa fitting the Z Wave contact lens??

Any feedback on these lenses would be much appreciated.

Regards
Richard McQueen
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Postby richbron » Thu Oct 04, 2007 4:00 pm

After second, third and even forth opinions, its official that my eyes were ruined by lasik and Astigmatic Keratotomy.

I have a minimal prescription yet cannot see short/long distance due to extreme Higher Order Aberrations. I have also been advised that the AK cuts tun through my flap - meaning any manipulation of the flap could literally tear them.

My vision is not corrected by glasses nor soft contacts.

I am currently being fit with RGPs - had the first lens fitted 3 months ago and I am now on my 12 lens (for the left eye - right eye is OK). I am happy with the fit but the vision is not great in the left eye. There is a persisitant astigmatism coming through which cannot be addressed - hence having tried 12 lenses. On the left eye I have a big crater (thanks to Lasik). We have sampled lenses that vault this crater, however no matter what lens I try, 1.25 D of astigmatism comes through.

I am feeling extremely frustrated as I live from one headache to the next. I am very convinced that my problems are due to the AK and not Lasik (The 4 months between Lasik and AK I happily wore glasses with 20/20).

One positive about the RGPs is my starbursts are managed with the lens, however having 1.25D means I have a blurry outlook anyway.

Has anybody had similar experiences fitting RGPs??
richbron
 
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Postby DryEye » Thu Oct 04, 2007 4:26 pm

Richbron:
I read an article the other day on lasik outcomes.
The article was entitled "Eye Surgery leaves many with Problems" from a North Carolina newspaper. It was informative and should come up by doing a google search.
It mentioned two contact lens company's that may help.
MedLens, Inc. and SynergEyes - They come up doing a google seach
Have you tried either one of these?
This site probably has other options to try as well.
We're you seen by anyone in the states here?
Hang in there - Things have a way of working out.
Let us know on your progress.
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