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OD panel members voice concerns
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BLOOMINGTON, Ind. — The panel that voted four to three to recommend approval of the Visx excimer laser for treatment of astigmatism included two optometrists, both of whom voted against the recommendation.
Food and Drug Administration Ophthalmic Devices Advisory Panel members Mark A. Bullimore, MCOptom, PhD, and P. Sarita Soni, OD, explained to Primary Care Optometry News why they voted the way they did.
Dr. Soni, who has served on the panel for 3 years and is an associate dean at the University of Indiana Optometry School here, had two concerns: the number of patients involved at the upper range of astigmatic correction, and the potential for a shift in the axis of correction in patients with less than 1 D of astigmatism.
"One reservation is that the number of patients we had at the upper range of astigmatic correction was too low," she said. "At a higher magnitude of cylinder, the zone that you're affecting becomes smaller. I didn't think we had enough data to look at safety concerns."
Dr. Soni said European studies presented by Visx used larger numbers of patients, but she felt "the European studies didn't consider visual aspects such as glare and night vision very carefully," she said. "If Visx was seeking approval, the company should have looked at safety and effectiveness at the higher ranges."
She was also concerned about axis shift with lower degrees of astigmatism, as the panel voted to allow astigmatic correction for as little as 0.75 D. "At the lower magnitudes, from 0.75 D to 1 D of astigmatism, the Visx data showed that 15% of the subjects had up to a 30° shift in their axis. That's quite a bit."
Her concerns were exacerbated be cause many patients fall within the parameters of the new guidelines. "I know as an optometrist that it's difficult to pinpoint the axis on a low cylinder," Dr. Soni said. "However, we're going to have a lot of people with that kind of shift, and it can be avoided by careful and thorough refraction and pinpointing of the cylinder. I wanted to make sure that concern was heard."
Dr. Bullimore, an assistant professor at Ohio State College of Optometry, expressed concern about the ablation zone diameter being as small as 4.2 mm across the minor axis of correction. "Studies have shown that satisfaction, predictability and safety are all a function of ablation zone diameter," he said.
He said he also would have liked to see more U.S. research, although he granted that "the government has encouraged manufacturers to submit additional, international data, and that can be evaluated as well. Panel members, including myself, who voted no, alluded that we would have voted yes under other circumstances."
For Your Information:
- P. Sarita Soni, OD, can be reached at 800 East Atwater Ave., Bloomington, IN 47405; (812) 855-8436; fax: (812) 855-7045.