Higher Order Aberrations

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Higher Order Aberrations

Postby DryEye » Thu Mar 08, 2007 10:19 pm

If one tries to fix them will the laser do anything to one's refractive powers (ie lower order aberrations)?
Is there a rule of thumb number wise on what is considered to high for higher order aberrations or is it just what the person sees?
Could they become worse overtime (more starbursting, etc)?
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Postby LasikExpert » Thu Mar 08, 2007 11:29 pm

Higher Order Aberration (HOA) are optic anomalies that cannot be readily corrected with glasses. HOA are most often represented as the Root Mean Squared (RMS) of Zernike Polynomials derived from wavefront analysis. There is no universally accepted average HOA, but it appears that most patients with good vision are in the 0.33 to 0.40 HOA RMS.

Everybody has HOAs. Not only do we have them, but they are needed. Some individuals with a critical need for vision quality, such as sport figures and fighter pilots, have higher than this average HOA RMS, yet their vision function is excellent. This is because "seeing" is not only about "optics".

Recently doctors created a system that would allow a patient to look through a device and all HOAs would be removed. The patient would have "perfect" optics, live and in real time. With perfect optics, the patients complained about poor vision quality. After some HOAs were returned, patients noted vision quality improvement.

Lower Order Aberrations (LOA) are sphere and cylinder, which are normally represented in diopters in a common eyeglass prescription.

Contact lenses may correct some HOA, but not because of the lens. They may correct some HOA by gently reshaping the epithelium (outer layer of the cornea) and thereby making the eye a more perfect optic. Spectacles do not correct HOA.

HOAs change throughout our lives, usually become elevated. This would be expected, considering the exposure our eyes endure over time.

Excimer lasers reshape the cornea by removing tissue. This is a remarkably accurate process, however it is not perfect. As a general rule, HOAs are increased with all laser-assisted refractive surgery. As a general rule, HOAs are increased more with conventional ablation than with wavefront-guided or wavefront-optimized ablation. HOAs can be reduced during Lasik and similar cornea-based refractive surgery, but not very predictably.

The FDA has not approved any laser for the reduction of HOAs. They are approved for the reduction of myopia (nearsighted, shortsighted), hyperopia (farsighted, longsighted) and/or astigmatism (corneal irregularity). Wavefront data is used to create an ablation map, but that does not mean that the FDA approved the laser to "treat" HOAs.

Just because the FDA has not approved the device for this particular purpose does not mean that the laser cannot help resolve elevated HOAs. This is called an off-label use and is perfectly appropriate under scope of medicine rules.

Some HOAs - especially Spherical Aberration that contributes to halos at night - are commonly improved with a wavefront-guided enhancement surgery. It all depends upon how high the HOAs are before surgery and which HOAs are elevated. If they are very, very elevated, enhancement surgery is more likely able to help. If they are moderately elevated, then the probability of a reduction of HOAs is less.
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Postby DryEye » Fri Mar 09, 2007 12:05 am

So, I had VISX CustomVue in June 06 and recently (January 07) noticed more starbursts on car headlights. Always had a not so crisp and clear problem probably due to astigmatism.
I recently got a very good opinion and understand what my situation is now.

I used to wear Vertex Torics prior to lasik and saw well

(R) -3 -1.25 1.70
(L) -3.50 1.25 1.80

Lensmeter (does that read what one wore glasses wise?)
R -4.75 +1.25 089
L -4.75 +1.25 083

549 Cornea (OD)
546 Cornea (OS)

I saw two surgeons. One did a better job on the workup, but wanted to do Traditional. I went with Custom due to what I read about it being better & second surgeon recomending it.

Not sure how to read all the numbers before what I am now with all the tests done? I did get all paperwork, so I can try to make the best decision going forward and showed most recent opinion all the paperwork.

Current Refractive Readings
(R) +.75 -1.00 010
(L) +.75
I was told 80% of my right eye is due to astigmatism 20% higher order aberrations & slight hyperopia
My left eye all due to higher order abberrations w/slight hyperopia
I plan on trying out glasses to see if I enjoy better vision, which I believe will due to the astigmatism. I may end up tweaking prescription slightly and then decide if enhancement is worth doing.
I was told if I end up wearing glasses alot and enjoy better vision it could be done with potential for better vision. He did sound encouraged on what he found.
The surgeon did an excellent job of testing and explaining to me situation.

Questions:
Would this enhancement be a difficult one to do?
Do you think another highly skilled surgeon may see it another way?
Would an enhancement be possible and successful on astigmatism with the right surgeon?
I believe the wavefront readings by Alcon for Aberrations had my Right Eye (OD) Dominant Eye
Aberrations
DeFocus 0.59
Astigmatism 0.86
Coma .05
Spherical Aberration .36
Other .21
Refraction Readings for Right Eye from Alcon WaveFront
Refraction from WaveFront
Sphere .54 Diopters
Cylinder -0.90 Diopters
Axis 9 Degress
Match 63%
Diameter 6.50mm
My Left Eye Readings (OS)
Aberrations
DeFocus .36
Astigmatism .86
Coma .11
Spherical Aberration .40
Other .28
Refraction from WaveFront
Sphere .66 Diopters
Cylinder -.65 Diopters
Axis 23 Degrees
Match 53%
Diameter 6.50 mm

What does all this mean in your opinion?

I believe I have 476 Cornea left on my Right Eye and 466 Cornea on my left eye.

He did a good job doing other tests and looking at the lens and explaining how ones lens comes into play for vision (like I have read on this site before.) & how it will change overtime and affect one's vision quality & cataract potential.

I at least feel a better now at least knowing and gettign an explanation of where I stand, but would like your opinion on all this?

Is there anything else I should know or be doing before I consider enhancement?

Thanks!!!
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Postby LasikExpert » Fri Mar 09, 2007 4:24 am

DryEye wrote:Current Refractive Readings
(R) +.75 -1.00 010
(L) +.75


Your right eye is moderately hyperopic (farsighted, longsighted) and has moderate astigmatism. Your left eye is moderately hyperopic.

DryEye wrote:Would this enhancement be a difficult one to do?


Hyperopic correction is more challenging than myopic (nearsighted, shortsighted) correction. Astigmatic correction is more challenging than myopic correction. All amounts are relatively small. The difficulty would be in not overcorrecting you back into myopia, but a small amount of myopia would probably be better than a small amount of hyperopia when you become presbyopic after around age 40.

DryEye wrote:Do you think another highly skilled surgeon may see it another way?


Ten surgeons equals ten slightly different opinions.

DryEye wrote:Would an enhancement be possible and successful on astigmatism with the right surgeon?


Success is possible, even probable. How probable is not guaranteed by anyone.

DryEye wrote:DeFocus 0.59


This is wavefront-speak for sphere. In your case, hyperopia.

DryEye wrote:Astigmatism


Same as common meaning. The cornea is not spherical like the top of a ball, but is elliptical like the back of a spoon.

DryEye wrote:Coma


Horizontal coma means the top has a different refractive power than the bottom. Vertical coma means the left has a different power than the right.

DryEye wrote:Spherical Aberration


The center has a different refractive error than the outer edges.

DryEye wrote:What does all this mean in your opinion?


You are a little hyperopic with moderate astigmatism in one eye. HOA do not seem to be terribly elevated.

DryEye wrote:Is there anything else I should know or be doing before I consider enhancement?


Absolutely. Better is the enemy of good enough.

(8^)>
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Postby DryEye » Fri Mar 09, 2007 4:32 am

Thanks for the answers.
So, in your opinion unless things got worse and more noticeably blurrier this result is good enough?

Do you think the hyperopia gets better going forward in time?

If so, would the astigmatism become worse also?

I really do think it's the astigmatism that is the problem here. Is that the way you see it?

Why do you think the machine did not get my right eye astigmatism and my left it did get?

I guess I'll know more once I try the glasses and see how different things are visually.
All part of the journey in oder to make a decision for now
Thanks!
Last edited by DryEye on Fri Mar 09, 2007 4:58 am, edited 1 time in total.
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Postby DryEye » Fri Mar 09, 2007 4:57 am

One more question

You said "Horizontal coma means the top has a different refractive power than the bottom. Vertical coma means the left has a different power than the right. "

Does that mean I have different refraction powers throughout my cornea?

Did my contacts do a better job of being equal in refraction throughout my cornea and cover more of it (for refraction purposes) than what the laser has provided me with?

Is that normal with lasik vs contact lens wear vision?

Could an enhancement widen the zone similar to what it is when one wears a contact lens?

Thanks
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Postby LasikExpert » Fri Mar 09, 2007 5:27 am

DryEye wrote:Does that mean I have different refraction powers throughout my cornea?


Absolutely. Everybody does, with or without Lasik. Different corneal thickness, different refractive index, different refractive power. Usually small differences, but they are there.

DryEye wrote:Did my contacts do a better job of being equal in refraction throughout my cornea and cover more of it (for refraction purposes) than what the laser has provided me with?


An advantage to contacts is that they smooth the outermost layer of the cornea (epithelium).

The molecule of the plastic used for contacts is much smaller than the smallest cell of the cornea. The laser can only ablate to the accuracy of the smallest cell, which is about 5 microns across. When 12 microns equals 1.00 diopter of refractive change, you can see the limitation of corneal reshaping.

DryEye wrote:Is that normal with lasik vs contact lens wear vision?


I don't know about "normal", but reasonably common. Remember that Lasik is not about better vision, it is about the convenience of a reduced need for corrective lenses.

DryEye wrote:Could an enhancement widen the zone similar to what it is when one wears a contact lens?


Enhancement may be able to widen the zone, but your Spherical Aberration indicates that you really don't need a larger ablation zone. You just need your hyperopia and astigmatism corrected.
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Postby DryEye » Fri Mar 09, 2007 4:33 pm

Why do you think the machine did not get my right eye astigmatism and my left it did get?

Do you think the hyperopia gets better going forward in time?

If so, would the astigmatism become worse also?

Thanks
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Postby LasikExpert » Fri Mar 09, 2007 5:10 pm

DryEye wrote:Why do you think the machine did not get my right eye astigmatism and my left it did get?


It looks like the astigmatism was detected.

DryEye wrote:Do you think the hyperopia gets better going forward in time?


It is possible, but not likely. You are past the six month point and your corneas should have stablized by now. Changes can happen after six months, but not something like regression of an overcorrection into hyperopia.

DryEye wrote:If so, would the astigmatism become worse also


The changes you would experience this late after surgery are the changes you probably would have experienced without Lasik. Yes, astigmatism can change, but it would not likely be due to your previous surgery.
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Postby DryEye » Mon Mar 12, 2007 4:03 pm

Did you mean above that the machine did not detect the astigmatism?
Does me being slightly hyperopic cancel out my astigmatism a bit because I don't think I notice it the that much. They say I see 20/20, but I guess the difference is in the small details.
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