LETTERS

have been attempted to improve the situation. The second is a very real and unfortunate problem. Al­though refractive surgeons are now using larger ablation zones than in earlier cases, we are limited in how large we can make the optical/ablation zone. Adding to this problem is the fact that certain patients, as in Mr. Nixon's case, have naturally large pupils that dilate to an even larger diameter in dim light. Despite excellent centration, as in this case, visual aberrations arise.

To prevent problems and unhappy patients, our preoperative assessment must include pupil size in normal and dim light, and we must warn patients who may be at risk for problems. These patients qIay not be good candidates for refractive surgery depending on their visual needs/expectations. If a patient is informed and would like to go ahead with treatment, myopes over 6.00 D may be treated with the tapered transition zone option with the Meditec laser. This allows for a more gradual transi­tion between treated and untreated areas and may reduce aberrations. Mr. Nixon's corneal topographical maps show a very abrupt change between treated and untreated areas. This is likely a factor in his visual problems,

compounding the optical zone-pupil size mismatch. Mr. Nixon's refractive error is not stated in the

letter. I believe he has two options. One would be to try a miotic agent such as a weak concentration of pilo­carpine. Although this is the minimal intervention, it does mean using drops every day.

The second option, which may improve but not eliminate his symptoms, would be a re-treatment to enlarge the optical zone to 7.0 mm. If he has no refractive error now, one may be induced by any re­treatment. However, based on a similar case at our clinic, he may benefit from a treatment of -1.00 D with optical zone 7.0 mm, stopping after a specific number of scans at 5.5 mm; reprogramming to do -0.50 D with optical zone 7.0 mm, stopping after a

specific number of scans at 6.0 mm; then reprogram­ming to do -0.50 D with optical zone 7.0 mm, stopping after a specific number of scans at 6.5 mm. One would have to review the corneal maps carefully

and obtain computer program data to determine the number of scans required at each step.

Mr. Nixon's letter reminds all refractive surgeons of the importance of pupil size in refractive surgery.

SUEDA AKKOR, MD v,mcouver, British Columbia, Canada

Preoperative evaluation of the potential refractive surgery candidate's pupils under both mesopic

(medium) and scotopic (low) lighting conditions will help reduce the incidence of the unhappy refractive patient or at least prepare and forewarn him or her of this potential problem during informed consent.

In general, I strongly warn patients with pupils greater than 7 mm under scotopic and greater than 6 mm under mesopic lighting of the increased likeli­hood for night vision difficulties such as glare and halos. The few patients I have seen with excellent daytime acuity and miserable symptoms at night sec­ondary to either small ablation zones with normal or

large pupils or 6 mm ablation zones with large pupils have benefited markedly from the use of weak miotics during times of low illumination. I have also found this to be useful in treating patients with symptomatic mildly decentered ablations and in patients with halos from multifocal intraocular lenses.

Pilocarpine in concentrations as low as 0.25 and 0.125%, 30 minutes before dusk, will usually constrict the pupil adequately and not result in a significant myopic shift or brow ache. Also, chronic use of a miotic two to three times a day will eventually result in an overall smaller pupil diameter under scotopic lighting conditions, alleviating the need for chronic lifetime use.

RICHARD S. HOFFMAN, MD Eugene, Oregon, USA

H alos, glare, and decreased contrast sensitivity are well-known side effects of LASIK when used to

treat high myopia. Although these side effects are usually temporary, especially with multizone ablation, we can assume that this was not the case for Mr. Nixon. Topography demonstrates well-centered corneal flatten­ing with no evidence of central island. With an ablation zone of 5.5 mm, the ideal pupil size would be 4.5 mm or less. Given the severity of this patient's symptoms, I

would recommend the use of low-dose pilocarpine as required. This treatment carries minimal risk and may allow the patient to return to the lifestyle he seeks.

KEITH C. CHARLES, MD Mount Dora, Florida, USA

In the article "Alcohol Removal of the Epithelium for Excimer Laser Ablation: Outcomes Analysis" (October 1997, pages 1160-1163), reference 2 was incorrectly cited in the discussion section after the following sentence: "We have had some experience with the Amoils brushes."

294 J CATARACT REFRACT SURG-VOL 24, MARCH 1998