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Dr. Q
Average Member
USA
27 Posts |
 Posted - 21 March 2002 : 09:20:18
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Often times, when patients are unhappy after LASIK, it is because they are having difficulty with the quality of their night vision.
The reason(s) that night vision difficulties develop are not fully understood or agreed upon by all surgeons. However, conventional wisdom states that the size of the pupil (the round, black space in the center of the colored iris) in dark conditions can tell us a lot about the relative risk of glare and halos after LASIK.
Basically, the thinking is that since the laser can only treat a certain diameter across the surface of the eye, if at night the pupil opens wider than the diameter that was treated, then light will enter the eye from untreated areas and since that light is out of focus, it is seen as glare or halos.
This thinking naturally leads to two conclusions. One, it is important to find out exactly how wide the pupil opens at night, and two, it is important to know what diameter the laser that the doctor is using can treat.
Traditionally, pupil size was measured in dark conditions by turning down the lights in the room and holding a small flashlight off to the side of the eye that was just bright enough to see the pupil without making it constrict. Then, a small card with known sizes of small black circles was held up next to the eye and the pupil size was matched to one of the circles on the card.
Today, however, many surgeons don't feel that this technique is accurate or reproducable enough for LASIK. These surgeons use an infrared "night vision goggle like" instrument that allows a reading in total darkness. The most popular brand of this instrument is the Colvard pupillometer.
Therefore, when discussing pupil size with your surgeon, it is helpful to also ask how the pupil size was measured.
I would like to stress, once again, that there may be other contributors to glare and halos at night. One such contributor may be simply that the LASIK procedure doesn't always eliminate 100% of one's glasses prescription and that the tiny bit of residual prescription may be more noticeable at night. Another contributor may be microscopic irregularities within the area that the laser treated.
Once again, we don't know or at least we surgeons haven't agreed upon every last factor that may cause glare or halos.
However, pupil size is commonly agreed upon as a major risk factor for glare and I believe that anyone who is contemplating LASIK should discuss their pupil size with their surgeon prior to surgery.
Dr. Q
For LASIK in Arizona, visit http://www.halevision.com |
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