How Does the Pupil Size Affect the Vision After Refractive Surgery?
In general, aberrations in the visual system become more prominent as the size of the pupil increases. These aberrations cause blurred vision as well as other changes in our vision such as glare and halos around lights at night.
What are Aberrations in Our Vision?
Low Order Aberrations
These are commonly known visual disorders which are myopia (nearsighted), hyperopia (farsighted), and astigmatism. These can be corrected by glasses or contact lenses.
High Order Aberrations
Everyone has these kinds of aberrations even if they have 20/20 vision without glasses. People with 20/20 without glasses will typically have less of these aberrations. Higher order aberrations cause much of the glare and halos seen by people. There are many different levels of aberrations and the most common ones we deal with presently are called coma, trefoil, spherical aberrations, and secondary astigmatism.
Pupil Measurement and Refractive Surgery
In order to achieve the best possible vision after a refractive surgery procedure, the pupil size should be measured.
Pupil Measurement with Observation
The common method used in the eye doctor’s office is to examine the pupil size using a card with black circles of sizes from 2-9 mm. The size of the patient’s pupil is compared to the circles on the card. This is done in dim light and bright light.
This method is satisfactory for routine office visits but other methods are more accurate for refractive surgery.
Pupil Measurement with the Procyon Pupillometer
This device captures the pupil size in various levels of light in an objective accurate manner.
Pupil Measurement with the Colvard Pupillometer
This device measures the pupil size using a superimposed reticle inside the instrument.
Pupil Measurement with the Pupilscan
This device uses infrared imaging to digitize the size of the pupil.
Pupil Measurement with the Neuroptics
NeurOptics’ Instrument
The targeting system locates the pupil and locks onto it and then measures the pupil size with different levels of the light.
Discussion of Pupil Sizes and LASIK
Originally, it was felt that pupil size was related to the amount of glare and halos after Excimer laser surgery. There are studies recently that have shown that pupil size does not have any relation to the amount of halos and glare after Excimer laser surgery. Some of this may be due to newer technology with wavefront laser surgeries.
Summary
Pupil size is still an important measurement in the work-up for refractive surgeries. The possibility of glare and halos should be discussed with the eye doctor performing the surgery. It does appear that newer technology in the lasers has made pupil size less important in the visual outcome after surgery.
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