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Home > Archive > Lasik Eyes Surgery > December 2005 > Now I know two reasons why laser surgury can give better vision(probably only accuracy
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Now I know two reasons why laser surgury can give better vision(probably only accuracy
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| This guy had wavefront PRK which still induces aberrations, however
read what he said.
Dry eyes - yes, and still every once in awhile, and more sensitive to
smoke/dust than before. Night vision and contrast are both great!
The other thing for me is my vision is WAY better than it was with
contacts because after sooo many years of wearing them, my eyelids had
become irritated and, even though I had daily disposables, they were
rapidly depositing film on the lenses to protect themselves, and
smearing my vision. I doubt you have the same problem, but it was a
factor.
Ace says: He was not getting the best possible vision from contacts due
to the intolerance to them. I bet he was seeing better with contacts
when he used to tolerate them fine vs. his new PRK eyes. He does not
remember or have a reference to contrast pre-op so of course he thinks
its great. Had he done one eye at a time, he may have noticed the loss
of contrast, even if only slight. Eye and others are right, all forms
of laser surgury damage every eye. You lose some nerves in the cornea
which will result in dry(er) eyes which can get worse as you get older.
Older women are very suspectable to dry eyes.
Another reason is the minification of glasses. It can be significent
enough if you have more than a little myopia to push you over the end
and not be able to see the line because its too small. Take someone
whos say a -6 and sees 20/20 piece of cake with glasses. However when
shown the 20/15 line, he just cant because its too small! refractive
surgury or contact lenses would also let him see 20/15. However youll
get more aberrations with laser. If your lucky and end up with "not too
many" induced aberrations your visual accuracy might not suffer and
quality only suffer a little. Many people take a big hit in quality and
even lose one more lines in visual accuracy with enough induced
aberrations. You could see haze, glare, ghosting, starbursts, halos and
still (barely) make out some of the 20/15 and be considered "20/15"
even though quality wise its not (quite) perfect.
Additionally, this is what some say:
Despite what many claim they experience, you cannot have better vision
post PRK than you would have pre-PRK with correction. All types of
refractive surgery induce higher order aberrations. Even customized
wavefront ablations. The aberrations that wavefront guided ablations
induce are just not as severe.
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| Glenn - USAEyes.org 2005-12-24, 11:00 am |
| On the whole, all excimer laser assisted refractive surgery techniques
induce higher order aberrations (HOA) as presented in Zernike
polynomials, however for the vast majority of people that inducement
does not translate into a degradation in vision quality and some (not
predictable and a minority) actually have a reduction in HOA.
There seems to be a threshold that varies from patient to patient
where HOAs become problematic. Some HOA are more problematic than
others. One of the reasons we highly recommend a wavefront analysis
for everyone before any type of refractive surgery is because this can
determine the level of naturally existing HOA.
If a patient is very high, but has no vision symptoms, then refractive
surgery may put them through that threshold and into poor vision. If
the HOA is very low, even a small increase may be very noticeable. In
all cases, the HOAs need to be evaluated just as much as the
prescription to determine if there is an elevated risk of a poor
outcome.
Glenn Hagele
Executive Director
USAEyes.org
"Consider and Choose With Confidence"
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
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| Glenn, pupil size is a big factor. The VISX aberrometer only measures
to 6 or 6.5mm, can't recall the largest zone possible for a wavefront
map... but it's no larger than that because they don't WANT you to
know what's happening in the periphery. Especially POST-op when the
average LASIK patient experiences a 28- to 46-fold increase in
aberrations as the pupil dilates from 3 to 7 mm. See the reference
below.
http://www.ncbi.nlm.nih.gov/entrez/...st_uids=9932992
American Journal of Ophthalmology
Volume 127, Issue 1 , January 1999, Pages 1-7
Comparison of corneal wavefront aberrations after photorefractive
keratectomy and laser in situ keratomileusis.
Oshika T, Klyce SD, Applegate RA, Howland HC, El Danasoury MA.
Department of Ophthalmology, university of Tokyo School of Medicine,
Japan. oshika-tky@umin.ac.jp
Glenn - USAEyes.org wrote:
> On the whole, all excimer laser assisted refractive surgery techniques
> induce higher order aberrations (HOA) as presented in Zernike
> polynomials, however for the vast majority of people that inducement
> does not translate into a degradation in vision quality and some (not
> predictable and a minority) actually have a reduction in HOA.
>
> There seems to be a threshold that varies from patient to patient
> where HOAs become problematic. Some HOA are more problematic than
> others. One of the reasons we highly recommend a wavefront analysis
> for everyone before any type of refractive surgery is because this can
> determine the level of naturally existing HOA.
>
> If a patient is very high, but has no vision symptoms, then refractive
> surgery may put them through that threshold and into poor vision. If
> the HOA is very low, even a small increase may be very noticeable. In
> all cases, the HOAs need to be evaluated just as much as the
> prescription to determine if there is an elevated risk of a poor
> outcome.
>
> Glenn Hagele
> Executive Director
> USAEyes.org
>
> "Consider and Choose With Confidence"
>
> Email to glenn dot hagele at usaeyes dot org
>
> http://www.USAEyes.org
> http://www.ComplicatedEyes.org
>
> I am not a doctor.
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| Glenn - USAEyes.org 2005-12-24, 6:02 pm |
| The "Eye" statement that the average LASIK patient has a 28 to 46 fold
increase in HOA as the pupil dilates is very misleading.
All persons have an increase in HOA as the size of the pupil
increases, whether or not they have had LASIK. The larger the pupil,
the greater the amount of aberrated light reaches the retina and is
"seen". There is a cumulative effect when focused light is passing
through any aberrated medium, and the natural untouched cornea is an
aberrated medium.
I really doubt that "Eye" knows what surgeons do or don't want
patients to know, but the limitation of ablation zone size with a
wavefront-guided ablation is well documented and public, and the issue
of pupil size v. ablation zone is also well known, albeit
controversial. See
http://www.usaeyes.org/faq/subjects..._pupil_size.htm for details.
Wavefront-guided ablation is not appropriate for every patient for
many reason. The issue of pupil size and ablation zone is just one of
the many factors that will be evaluated by a competent surgeon.
Glenn Hagele
Executive Director
USAEyes.org
"Consider and Choose With Confidence"
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
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