Point/Counterpoint: Is Pupil Size Important in Refractive Surgery? (Part 1)
Some physicians believe that because excimer lasers have become so sophisticated and their ablations are so smooth, that pupil size is no longer an issue in refractive treatments. I cannot agree with this opinion, however, because I have seen many patients for whom pupil size does matter. Although I have not conducted a formal study pertaining to pupil size, I have treated many refractive surgery patients over the past 10 years who are miserable because they have good vision, but high incidences of nighttime glare and halos. Patients who have small pupils are usually highly satisfied with their results, but some patients with 6.5- to 8-mm pupils are truly unhappy. A few of these patients are so incapacitated that they are unable to drive at night. In addition, I have observed in a dark refracting lane that many patients' complaints disappear or are significantly minimized when a penlight is directed into their nontested eye, thus constricting the pupil in the tested eye through the consensual light reflex. These same patients often respond well to Alphagan (Allergan, Inc., Irvine, CA), which reduces pupillary dilation in the dark as first described by Jay McDonald, MD. Measuring pupil size and informing patients with large pupils that they may be at increased risk of experiencing an increase in night glare and halos, especially when they require corrections over -4.0 D, is very important in evaluating patients for refractive surgery. This is especially true if the laser being utilized cannot ablate larger optical zones and blend zones.
DECIPHERING THE DATA
A large pupil does not guarantee that a patient will experience any difficulty with nighttime vision—we have all had patients whom we expect will experience trouble, but do not. There is a highly variable patient response in refractive surgery. Nevertheless, as surgeons, we must not trivialize the risk of patient outcomes. A few studies have determined pupil size to be unimportant; a recent study published by Stephen Schallhorn, MD, stated that pupil size is perhaps not as significant as previously thought. In that study, Dr. Schallhorn correlated patients' good results with their amount of correction and pupil size having higher incidences of nighttime halos and glare. I agree that a patient with a 7-mm pupil and a prescription of -3.0 D is far less likely to be symptomatic than a patient with a 7-mm pupil and a refraction of 7.0 D. The more tissue the surgeon must remove, the greater the patient's risk of halos and glare. Edward Manche, MD, and Mihai Pop, MD, also conducted recent studies that show that pupil size did not correlate very well with patients' symptoms, but those studies were conducted with 60 to 80 eyes. If a study were conducted involving thousands of refractive surgery patients, some would emerge who were truly unhappy with their results.
THE IMPORTANCE OF MEASUREMENTS
It does not matter how, but pupil size must be measured. I believe that the best method is with an infrared device, such as the Colvard Pupillometer (OASIS Medical, Inc., Glendora, CA), the Pupilscan, or the Procyon P2000SA pupillometer (Keeler Instruments, Inc., Broomall, PA). In my practice, we bring our patients into a completely dark room and measure their pupil size in the least amount of light possible. This setting tests patients' maximum pupil size (such as in a dark, moonless night). We then try to match the ablation diameter of their pupil whenever possible. If the patient has a 7-mm pupil, I always ablate a 7-mm zone. I may even ablate an 8-mm zone using the LADARVision Excimer Laser System (Alcon Laboratories, Fort Worth, TX). We have treated some patients now that we would not have treated 2 years ago when we could only create 6.5-mm ablation zones. For the most part, these patients are doing well. Some say they experience mild glare, but they are not incapacitated by it. I believe that our job as surgeons is to first measure pupil size. If the patient has an unusually large pupil, regardless of their refraction, I feel that we must inform the patient that he or she is at a potentially increased risk of glare.
NIGHTTIME SYMPTOMS AND ABERRATIONS
Most patients who complain of nighttime problems have a greater incidence of spherical aberrations, and surgeons can now measure these aberrations using wavefront technology. Other types of aberrations such as coma, in addition to spherical aberration, contribute to symptoms. Wavefront technology can determine net RMS values for these aberrations, and patients who have many complaints usually have high readings. Interestingly, if the surgeon constricts the patient's pupil and then re-measures the wavefront, all the patient's aberrations disappear. The reason is that although the cornea still contains the abnormality, the pupil is now smaller than the peripheral area where the aberrations allow light to enter through the retina. Therefore, the pupil blocks any erroneous light waves from reaching the retina, and patients do not experience the effects of their higher-order aberration. Any surgeon performing wavefront studies can see that patients' aberrations—coma as well as spherical—are highly correlated to pupil size, and that reducing it eliminates these symptoms.
CASE IN POINT
I recently treated a case that specifically illustrates my point. This male patient had no negative ocular symptoms when his pupils were around 5 mm, but experienced significant glare and ghosting when they were larger than 6 mm. At pupil measurements of 5.5 mm, this patient shows very low spherical aberration and coma reading. At 6.5 mm, however, wavefront maps show that both of these values increase considerably. This also correlates with his symptoms, and therefore proves the importance of pupil size. The patient was -4.0 -1.50 X 115 preoperatively, and his pupils measured 6.5 mm. He underwent a 6.5-mm ablation with a 1.0-mm blend zone on the LADARVision laser (Alcon Surgical, Fort Worth, TX). His postoperative UCVA was 20/20, and he had a well-centered ablation on topography. His pupils are now 5 to 5.5 mm on Alphagan, which provides significant relief of his symptoms.
PATIENT MANAGEMENT
Although I know some ophthalmologists feel otherwise, I believe that as surgeons, we have a responsibility to warn patients of their potential risks. I have a personal philosophy with borderline patients. First, I never treat both eyes simultaneously, particularly patients with larger pupils. I tell them that I believe they will most likely have good outcomes, but I do not know that definitively. For that reason, I will treat their nondominant eye first. I create the largest zone I safely can, based on the amount of correction the patient requires (you cannot always perform an 8-mm ablation zone if the cornea is too thin or if the patient has a high correction). At times, I will recommend PRK or LASEK if corneal thickness does not permit a larger ablation diameter.
Once the surgery is complete, I tell my patients to live with their results for as long as they choose—a few days, a week, or longer, and I tell them to specifically go out at night and compare the vision of the treated, nondominant eye with the eye that is still wearing the contact lens. If the patient tells me that the lasered eye is much worse than their contact lens eye, then I will not treat the other eye until those symptoms improve, as they do in many patients. Patients may be symptomatic for the first few weeks, and then they adjust. There is a tendency for most to improve, but not all, and some have never had the second eye treated because they feel there is a huge difference in the quality of vision between the treated and untreated eye. For this reason, I feel it is a mistake to treat both eyes at once in these potentially high-risk patients.
HELP IN A BOTTLE
One treatment that we can now offer patients suffering from nighttime symptoms, in addition to larger optical zones, is the use of Alphagan. Dr. MacDonald shared in an online forum approximately 2 years ago that Alphagan prevents the pupil from dilating in the dark. Since then, Alphagan has proven very helpful for some patients suffering nighttime symptoms. Patients self-administer one drop about 30 minutes before sundown, and their pupil decreases 1 to 2 mm from its normal size. Alphagan can dramatically decrease patients' incidence of night glare when used in this manner.
INFORMED CONSENT
I believe that pupil size will always matter in refractive surgery, regardless of what technological advancements we make. It will always be important to correlate patients' symptoms with their pupil size and to try to make their ablation consistently as large and as safe as possible from a thickness standpoint. Even more importantly, patients should have a proper, informed consent form that advises them that they are at potential risk for nighttime symptoms. Some surgeons believe that they should not have to inform patients of this risk, but I feel those at higher risk, especially those with larger pupils, have the right to know.
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