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Pupil Size and LASIK
The PUPIL is the central opening of the iris. The pupil allows light to enter the eye, like the shutter of a
camera. Muscles in the iris respond to changing light conditions and cause the pupil to change size.
The brighter the light, the smaller the pupil gets and the dimmer the light, the larger it gets. In addition
to light, the pupil responds to a focusing mechanism in the eye called accommodation, and to various
medications.
The safety and effectiveness of laser in situ keratomileusis (LASIK) and advanced surface
ablation(ASA),including photorefractive keratectomy(PRK) and LASEK, has been repeatedly
demonstrated. However, patients who fall in the moderate and high risk areas of the traditional (or
conventional) VISX grid may experience night vision difficulties such as halos around lights, glare, and
ghosting. These symptoms are caused by corneal irregularities, which are related to pupil size. Halos
are specifically caused when the pupil is larger in dim light than the area treated in the center of the
cornea. The higher the prescription, the smaller the effective area of treatment, and the greater the
potential for halos.
For this reason, we now have available advanced laser technology to significantly minimize the risk of
the potential effects of pupil size on your vision.
Your pupil size measurement shows that your pupil is _____ mm right eye and _____ mm left eye in
dim light. According to the traditional Visx glare and halos grid it shows that you are at
______________ risk of experiencing halos at night, affecting the quality of your vision.
If your cornea is thick enough, our advanced laser systems (the Wavelight Allegretto and VISX Custom
Vue S4) cover the pupillary aperture of up to 9mm. This feature creates a more gradual change from the
optical zone out to the non-treated area. In either case, there is no guarantee that halos or starburst effect
will be eliminated entirely. If halos persist following LASIK and are problematic, you may get some
relief with the use of an eye drop that can be used on a daily basis to help make your pupil smaller. Not
all patients like to use this drop. If your doctor thinks you may be at high risk for halos, you may want to
see if you tolerate these drops by trying them before you undergo laser vision correction.
Because the treatment zone is directly related with the depth of the treatment (e.g.: your corneas might
be too thin in relation to the amount of treatment to be performed) not all patients are good candidates
for the larger or expanded treatment zones. If that is the case, your doctor will discuss with you the
different alternatives that are available.
If you are already experiencing these symptoms at night with your contacts or glasses, you should
expect them to continue after LASIK surgery.
Large pupils are not, by themselves, a contra-indication to LASIK procedure. It is, however, a fact that
must be taken into consideration. Please, feel free to discuss any questions you may have with your
surgeon.
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