The refractive surgery industry (RSI) is divided into two opposing camps on the effect of pupil size on vision quality after laser vision correction (LVC). These are:

1. Pupil size is irrelevant
2. Pupil size is critical

Much of the professional conversation about pupil size vs. optical zone size is carried out in the junk literature, in monthly publications such as Ophthalmology Times, Ocular Surgery News, and EyeWorld. To make any sense out of this information, a lot of which is available on the web, it helps to know a little bit about the influential people and their industrial prejudices. Read on.

1. Pupil size is irrelevant

Doctors who use the VISX laser platform currently have two choices for the optical zone: 6.0 mm and 6.5 mm. If your maximum dark pupil diameter is greater than 6.5 mm, there is no way that a VISX optical zone is going to completely cover your pupil. The average dark pupil diameter for individuals in their 20’s and 30’s is about 7.0 mm. So this circumstance applies to a lot of people. For a long time VISX stated that there was no connection between the dark pupil diameter and "patient satisfaction". This type of pronouncement has grudgingly given way to statements about whether patients felt their night-time glare and halo symptoms were increased, decreased, or unchanged after LVC. This is still remarkably subjective feedback that the typical person like you considering LVC cannot interpret in his own context.

Examples: for people who wear glasses, glare is usually correlated with the strength of the prescription, the quality and accuracy of the lenses, and dirt. For people who wear soft contact lenses, glare is correlated with how dirty and dry the lenses are. Patients who wear soft toric lenses (which correct for astigmatism) may spend a lot of their lives somewhat out of focus due to rotation of the contacts. Patients of this sort may very well experience a decrease in glare or halo symptoms at night after LVC. Make a check mark in the ‘decreased’ column and report the data. Thank you.

You, however, either 1) wear good quality glasses that are clean, and/or 2) are modestly nearsighted with little astigmatism, and/or 3) wear non-toric soft contact lenses that are clean and well-maintained. You are not actually sure whether you experience glare currently, and your surgeon may or may not have shown you a photograph or video that demonstrates significant glare in a real-life situation like night driving. Assuming you have no glare, you cannot have a decrease in glare after surgery. You are therefore unlike an unknown, but possibly substantial, portion of the patients that undergo LVC. For you, the only way to change is to go up the glare scale. Think about it.

Anyway, back to VISX. The latest pronouncement by the VISX cogniscenti is that large-pupil patients being treated with a 6.5 mm optical zone and a blend zone out to 8.0 mm experience no change, or a reduction, in glare/halos, regardless of the dark pupil diameter. [“Surgeons find no correlation between large pupil size and refractive complications.” EyeWorld: February 2003.] The remarkable corollary admission is that this is not true for treatment with a 6.0 mm optical zone plus a blend zone. That is, the dark pupil diameter is predictive of worsening glare/halos in patients treated with the older 6.0 mm optical zone: larger pupils lead to worse vision quality. Now this is useful information.

The Lone Dog, being a big-time skeptic of the intellectual integrity of the RSI, asks himself . . . why the sudden spasm of honesty? What follows is speculation, but hopefully it’s enjoyable reading.

First, lawsuits are increasing. Several sometimes-successful pressure points for litigation have developed: 1) you measured my pupils wrong you dumb bastard, and 2) you therefore did not adequately inform me of my risk of vision quality loss, or 3) you did not plan and perform my surgery in such a fashion as to minimize my risk of vision quality loss. This has led to end-user pressure on VISX (and other laser companies) to decrease the likelihood of poor vision quality outcomes. They are accordingly upping their capabilities for optical zone size and adding refinements to the software (e.g., blend or transition zones).

Second, there are some interesting personalities in the VISX Theater. Steve Schallhorn MD is the director of the refractive surgery program for the US Navy. He has a principal employer — the United States government — which is keenly interested in preventing night glare after LVC in its fighting forces. Therefore, his incentives are mostly aligned to the advantage of the great unwashed, which is to say you and me. The quote in EyeWorld regarding problems with 6.0 mm optical zones is credited to Schallhorn. Confusingly, he also acts as an expert witness on the defense side of the “pupil size doesn’t matter” argument. He’ll be an interesting doc to watch, since even with a uniform on it’s probably uncomfortable sitting on that fence.

Douglas Koch MD is the director of the refractive surgery service at Baylor University in Houston, Texas. He is also the Editor-in-Chief of the Journal of Cataract and Refractive Surgery. In addition to being a pretty decent guy (hated by few, respected by most in the RSI), he is a principal US investigator for VISX. Although it may be a spasm of wishful sentiment, the Lone Dog thinks that Koch has put the brakes on some of VISX’s wilder promotional excesses to both physicians and the public. VISX has been cautious and patient about releasing its wavefront technology, which Koch is investigating. The JCRS has improved markedly under his stewardship. Does the guy sleep?

So where does this leave you, the eager LVC wannabe? Well, unless your pupils are really really huge and your prescription is funky (these are LD caveats, not VISX caveats), 1) if you are treated on the VISX platform by a reputable, experienced surgeon who uses a 6.5 mm optical zone and some type of blend zone, and 2) if the laser actually delivers what it was programmed to do, and 3) if you experience no other errors of surgical planning (e.g., wrong refraction, poor candidate for other reasons), and 4) if you experience no intra-operative or post-operative complications…you will probably be OK. Assuming any glare is induced by the procedure, it may be 1) less than you currently experience with your out-of-date glasses and your dirty contact lenses, or 2) something you can live with that you consider a reasonable trade-off for what you have gained.

2. Pupil size is critical

Several other laser platforms have software that allows for surgeon-selected optical zones greater than 6.5 mm. The typical range is 5.5 to 8.0 mm in 0.5 mm increments. Throw in a 1.0 mm transition zone, and all those big-pupil patients are in the catbird seat. This is presumably what Alcon, maker of the Summit Autonomous LADARvision laser, believes. Man, with a name like that, it must be some laser, although Alcon cannot specifically promote the large-zone capability because it was never approved by the FDA.

Doctors who use large-zone lasers believe that pupil size is critical, and that every effort should be made to get the optical zone to be larger than the dark pupil diameter. If you paid a lot of money to get a laser that can make a 7.0 mm or larger optical zone, are you going to accept that this capability is of no value? No way. It gets philosophical here, but the philosophy is driven by the investment. Owning/using a VISX laser = 6.5 mm is usually fine no matter what; owning/using an Alcon laser = 6.5 mm is a travesty of LVC for patients with 7.0 mm pupils. You Philistines with your ancient software and your broad-beam lasers etc . . .

Who are the Alcon luminaries? Brian Boxer-Wachler MD, who recently skipped out of UCLA to set up a private refractive practice in the City of Angels, is a decent thinker about corneal optics and has published good work on the effect of long-term healing or remodeling on the final size of the optical zone. He is solidly behind the “bigger is better” philosophy. Dr. Boxer-Wachler has stepped outside the corporate box on occasion to provide information of value to all refractive surgeons and their patients. He has a web page out there somewhere.

Alcon’s main public face is Marguerite McDonald MD in New Orleans. About Dr. McDonald’s analytical methodology, the LD humbly inquires: why is her topographer set in 1.5 diopter increments? You say, huh? Stay with me now . . .

A topographer is an instrument that measures the way that the cornea curves. If the cornea was flat, it wouldn’t focus light (a window doesn’t change the focus of light, although if it is dirty it can change the clarity of the image). The measurement of the cornea’s focusing power, i.e. its curvature, is in a unit called a “diopter”. The sole and entire and absolute bottom line of LVC is that the laser is supposed to change the curve of the front surface of the cornea. So if you want to know that your laser hardware is behaving, and your laser software is smart, you might want to look at topographies on some of your LVC patients after surgery, right? For a long time this basic quality control concept was . . . er . . . not emphasized by the RSI because the major end-point for the FDA laser trials was the visual acuity (‘how low can you go’ on the eye chart), and RSI folks didn’t want the FDA or anyone else getting a look at the post-op topos. In the LD’s cynical opinion, this is because, using the early lasers, the topographies looked like the LD’s dog had chewed on them. A rotten cornea can still deliver good acuity, combined with terrible vision quality. This is the origin of the uber-myth that post-operative corneal topographies “don’t tell you anything”, by the way.

Okay, back to New Orleans. A typical cornea does not have the same curvature over its entire surface. A cornea that has undergone LVC for nearsightedness will be flatter in the center (lower diopters) and steeper around the edges. If you want to have good vision quality, it is important for most of the treated area of the cornea to be “on target”. It does seem to be the case that the cornea does not have to be absolutely perfect at each and every spot in the optical zone to deliver both good acuity and good quality, but there are limits. I can tell you that the limit is a whole lot less than 1.5 diopters. By setting her topographer’s monitor and printout scale to 1.5 diopter increments, Dr. McDonald cannot detect clinically important inconsistencies in the optical zone. A more useful method would be to set the increment to 0.5 diopter or less.

To put it another way, if you had a substantial region of cornea inside your optical zone that internally varied by 1.25 diopters, 1) it could cause symptoms, and 2) it would not be evident on a topography printout from Dr. McDonald. With me? This always causes a little twitch in the LD’s brain when he reads a throwaway article quoting her and her wonderful results with Alcon’s laser platform. Otherwise she seems like a nice lady.

Well anyway . . . let’s say that your friend Mike got treated by Joe Surgeon who uses the Alcon platform. Man, is he happy. So is Joe, who knows a good word-of-mouth referral source when he creates one. You go see Joe, but you’ve read this article and you’re thinking you want that other laser. Well, unless your pupils are really really huge and your prescription is funky (these are LD caveats, not Alcon caveats), 1) if you are treated on the Alcon platform by a reputable, experienced surgeon who uses an optical zone 0.5 to 1.0 mm larger than your dark pupil diameter (preferably 1.0 mm larger) and some type of blend zone, and 2) if the laser actually delivers what it was programmed to do, and 3) if you experience no other errors of surgical planning (e.g., wrong refraction, poor candidate for other reasons), and 4) if you experience no intra-operative or post-operative complications…you will probably be OK. Assuming any glare is induced by the procedure, it may be 1) less than you currently experience with your out-of-date glasses and your dirty contact lenses, or 2) something you can live with that you consider a reasonable trade-off for what you have gained.

This will be on the test. The VISX platform appears to be generally successful and to have an acceptable safety profile when a 6.5 mm optical zone with a blend out to 8.0 mm is used, even if your dark pupil diameters are larger than 6.5 mm. This is not a promise. You may still be pissed. But this is what you should shop for, and don’t accept a smaller zone without a clear explanation from your surgeon and some second thoughts.

The Alcon platform (and other wide-zone platforms) appears to be generally successful and to have an acceptable safety profile when the programmed optical zone is 0.5 to 1.0 mm larger than your dark pupil diameter. If the surgeon cannot (for various reasons related to you specifically) or does not make this choice, it does not follow that you will be OK with a 6.5 mm optical zone if your dark pupil diameters are larger than 6.0 mm. If there was no necessity for or advantage to using a larger zone on the Alcon platform, why build it? Why buy it? This is a different laser. It has different hardware, different software. Alcon is attempting to address the vision quality problem by going bigger on the zone size. VISX is addressing it some other way, which seems to be mostly working.

[Note from the LD: the laser manufacturers (VISX, Alcon) and the physicians (Schallhorn, Koch, Boxer-Wachler, McDonald) discussed in this article floated into the LD’s mind one Saturday morning. This article does not address several other laser platforms and many other prominent investigators. The sole intent is to provide LVC candidates with information that may help them to make more informed choices. If anyone out there feels dissed, I’m sorry. Regarding pupil size and optical zone size, the concepts discussed apply equally well to whatever laser platform your surgeon may use. So ask him.]