LASIK patients with large pupils often report night vision disturbances following surgery. These aberrations can be measured using a technique called wavefront aberrometry. The aberrations are part of a set of aberrations called High Order Aberrations (HOA). The specific HOA associated with large pupil LASIK patients are called Spherical Aberrations. Put simply the area treated during LASIK does not cover the entire pupil. This causes light at the outside edge of the pupil to scatter. Many large pupil LASIK patients report double and triple images, ghosting, starbursts, and halos. Collectively, this result of LASIK surgery is referred to as Night Vision Disturbances that many claim results when people with large pupils undergo LASIK.
So, if HOA can be measured why aren’t they recognized by ophthalmologists as the cause of Night Vision Disturbances? I asked an ophthalmologist the same question and was told that my understanding of how the eye works is incomplete. There is a phenomenon called Neural Adaptation that in theory allows LASIK patients to see past the scattered light entering their eye and form a “normal” image in the brain from an abnormal image on the eye’s retina.
Neural Adaptation is a fascinating subject. I found a very good website that explains part of the phenomenon at http://serendip.brynmawr.edu/bb/blindspot1.html. There are actually tests on this site that demonstrate how the eye compensates for the blind spot on the retina. The blind spot is the part of the retina where the optic nerve leaves the eye. This is a spot where there are no rods or cones so light hitting this part of the retina isn’t processed as part of an image.
Even though we all have blind spots on our retinas our brains can fill in colors and patterns and complete an incomplete image. It seems that our brains are hardwired to remove inconsistencies.
Many ophthalmologists tell large pupil LASIK patients that Neural Adaptation will remove HOA in the same way that it fills in the blind spot. Unfortunately, for many of these patients it doesn’t work. In the theory put forth by their doctors, patients' brains should adapt. In fact large pupil LASIK patients report that Neural Adaptation doesn’t remove the HOA. These large pupil LASIK patients wait for their brains to adapt, they give it time, and they honestly want to experience the miracle of Neural Adaptation that they have been promised. But it never comes.
So, they go back to their ophthalmologist and explain that their vision is bad, truly bad. Still, many doctors insist that these patients’ vision is good. They test at 20/20 or better on an eye exam so the surgery was a success. The doctors cannot see the patient’s problem even though the problem is directly in front of them.
These patients have entered ophthalmology’s blind spot. The story that ophthalmology has to tell is that LASIK is a positive, life changing experience. They tell us that it has changed millions of lives. This is the pattern and color ophthalmologists see. It closes over the complaining patients and removes the inconsistencies. The profession is hard wired to ignore anything that is inconsistent with the LASIK success story.
Gerard J. Dorrian