Pupil Size and LASIK
by Dr. Matthew Sharpe
- Seattle LASIK Surgeon
How Can Pupil Size Impact My LASIK Procedure?
The size of one’s pupil in dim light has long been discussed as a factor in the results of LASIK. As the practice of laser vision correction has evolved, physicians have learned that there are numerous factors in delivering a superb visual result for our patients. The effect that the size of one’s pupil has on vision is one of many factors in how we see after the procedure.
With the advent of Wavefront driven procedures, physicians are now able to analyze all the components of the optics of our eyes that cause blur in our vision. The major factors in our blurred vision are usually Nearsightedness, Farsightedness, and Astigmatism. These three factors can be corrected with glasses or contacts. However, everyone has some degree of other imperfections in the optics of their eyes. These other factors are called “higher order aberrations” and may contribute anywhere from 2% to 20% of the overall blur. The aberrations have names like “coma”, “secondary astigmatism”, “trefoil”, and “spherical aberration”.
The aberration that is most directly related to pupil size is “spherical aberration”, which causes a “halo” around lights at night when your pupils are at their largest. Spherical aberration is always increased when we treat a nearsighted person, because we flatten the central part of the cornea with the laser. Two very important factors besides pupil size in the quality of vision post-operatively are: the amount of correction and the size of the treatment zone.
For instance, if a patient with a -10 prescription, who has 7 mm pupils is treated with a 6.5 mm treatment zone, they will likely experience some increased haloes around porch lights at night. However, a patient with -4 prescription with the same pupils and treatment size will likely experience minimal haloes around lights, and be pleased with the result. If we could enlarge the treatment size much bigger than the pupil, it would minimize the spherical aberration, but it would require removing prohibitively large amounts of corneal tissue to do this. A better way is to perform a wavefront analysis and treatment of all the optical aberrations at once.
When our pupils are small, as they are during the day, most of the irregularities in our eyes are covered up. As the light decreases, the irregularities are exposed, which can cause haloes around lights to appear.
The only way to determine your specific aberrations and size of your pupils is to come in for a LASIK Consultation. During this Free Exam, we routinely perform wavefront measurements to help determine if you are a LASIK Candidate, and if you would benefit from a wavefront treatment.
In summary, the size of your pupils may impact your treatment outcome, but it is just one of many important factors in delivering superb results for you, as our patient.
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