To put it simply, performing a customized treatment entails fully correcting an individual's refractive error and aberrations to the extent of the scotopic pupil, because patients primarily notice distortions in their vision at nighttime. Additionally, enlarged pupils facilitate obtaining a better resolving capability when they stay in focus. Measuring the wavefront of an undilated pupil will not produce the maximum pupillary diameter to treat out to the periphery. Although the average scotopic pupil size is approximately 5.5 mm, some patients' pupils will be smaller or larger in dim light. Therefore, simply measuring a wavefront to an average pupil size will limit the distance into the periphery that the surgeon can treat. Many excimer laser manufacturers still believe that dilation is unnecessary, but some now require a dilated pupil measurement.

Ideally, the surgeon should gather information on a pupil sized approximately 7.0 mm to be able to treat at least 6.5 mm; this size pupil will produce a sufficiently large treatment zone. In the original FDA excimer laser approvals, standard zone sizes were 6.0 mm, but many surgeons would prefer to treat zones that are somewhat larger than that—6.5 to 8.0 mm. I believe that the best scenario is to treat a customized ablation zone of at least 6.0 or 6.5 mm and then create a blend zone that goes out to the periphery so that there is a smooth transition. In my opinion, this treatment approach will produce the best overall outcome.

I feel that measuring with a dilated pupil is even more important with customized ablations than with standard LASIK. Customized ablations carry a higher outcome standard and are subject to higher patient expectations; for instance, these patients will expect to receive better postoperative nighttime vision than their standard-LASIK counterparts. Better outcomes are even part of the claims that are being made in the FDA labeling of approval. For instance, part of the FDA labeling for the recent approval of the LADARVision CustomCornea wavefront system (Alcon Laboratories, Inc., Fort Worth, TX) includes less mesopic loss of contrast compared with standard LASIK, which is a big factor in helping to minimize visual symptoms such as glare and halos that a patient might experience at night. LADARVision is the first customized ablation platform to receive FDA approval, and all of its approvals were based on trials that dilated the pupils.

IMPACT OF PHARMACOLOGICAL DILATION
Some investigators have suggested that instilling dilating drops has the potential to produce a different wavefront than that produced when the same eye is dilated naturally by low-light situations.¹ Internal reports from companies, however, have described investigations showing no real change in the higher-order aberrations due to the instillation of cycloplegic drops.² Although I believe that certain cases will demonstrate some subtle differences in the aberration pattern between these methods, I do not think that the use of dilating drops will affect outcomes.

EFFICIENCY
Certainly, dilation is an extra step. A surgeon might reason that it is unnecessary for corneal topography, so perhaps performing wavefront measurements in dim lighting such that the pupil is enlarged will permit the capture of adequate information to create a treatment plan. I think some companies are inclined to follow this reasoning and their surgeons are following suit, but I believe that this method is not the best for the reasons I gave earlier.

Some surgeons may believe that it is a disadvantage that LADARVision users dilate the pupil when tracking during surgery, performing needless extra steps where ophthalmologists using other laser platforms do not. Regardless of whether or not a laser platform requires pupil dilation for eye tracking, dilation is the best means of fully and reproducibly capturing a wavefront measurement. One advantage of LADARVision is that, since it requires preoperative dilation, the surgeon may perform a wavefront measurement on the day of surgery and then immediately position the patient under the laser for surgery. Many other platforms can only track an undilated pupil, so dilating a patient preoperatively will necessitate waiting for the cycloplegic effect to dissipate prior to beginning the procedure. As a result, surgeons using these platforms may be inclined to perform wavefront measurements without dilation.

I obtain a wavefront map of the patient during the diagnostic workup and on the day of surgery in order to ensure that the measurements are in close agreement. I use the latter map as the basis of my treatment plan and perform surgery 5 to 10 minutes after capturing the wavefront measurement.

STANDARDIZATION
I believe that pupil dilation should become standard practice in customized ablation. As in every field, one company will pioneer a technique or device in the face of skeptics, but eventually the field will reach a decision on the issue. I believe that ophthalmology will move in the direction of dilation.

Ronald R. Krueger, MD, is Medical Director of the Department of Refractive Surgery, Cole Eye Institute, Cleveland Clinic Foundation, Cleveland. He receives research funds and travel support from Alcon Laboratories, Inc. Dr. Krueger may be reached at (216) 444-8158; krueger@ccf.org.

1 Fankhauser F, Kaemmerer M, Mrochen M, et al. The effect of accommodation, mydriasis and cycloplegia on aberrometry. Invest Ophthalmol Vis Sci. 2000;41:4:S461.
2 Pettit GH, Campin JA, McDonald MB. Alcon Custom Cornea Technology. In: Krueger R, MacRae S, Applegate R. Customized Visual Correction: The Quest for Super Vision. Thorofare, NJ: SLACK INC;2003 (in press).