Visx receives FDA approvable letter for excimer laser to treat astigmatism

Issue: March 1997

WASHINGTON — One month after the Food and Drug Administration (FDA) Ophthalmic Devices Advisory Panel voted four to three to recommend approving Visx's excimer laser system to treat myopic astigmatism between 0.75 D and 4 D, Visx received an approval letter from the FDA.

Receiving the letter is the last step before the product becomes available for marketing, said a Visx spokesperson, and the company will start talks with the agency about labeling issues for the system.

At its Jan. 14 meeting, the advisory panel recommended approval with three conditions: the labeling will restrict the minimum patient age to 21; patients between 21 and 30 will be told of the potential for an increased incidence of glare and halos for that age group; and Visx will train surgeons for astigmatic procedures.

The beam used in astigmatic correction is the same as for PRK without astigmatism and does not ablate any deeper into the cornea than a 6-D sphere treatment at the corneal plane, said Marc Odrich, MD, the medical monitor for the Visx study. Instead, the Visx system uses a software change in the keycard to create a radially asymmetric beam.

Three panel members voted against the recommendation after expressing concerns that not enough data were presented on U.S. patients to prove safety and efficacy for the range between 0.75 D and 1 D of astigmatism, as well as the range between 3.1 D and 4 D.

The FDA has final authority to approve the excimer. Director of the Division of Ophthalmic Devices A. Ralph Rosenthal, MD, said that the FDA could consider any or all of the panel member's concerns before approving the Visx excimer.

FDA analysis

Malvina Eydelman, MD, a clinical reviewer with the FDA, told the panel that clinical results differed between PRK for myopia and for myopia with astigmatic correction.

For example, Dr. Eydelman said, at 2 years' follow-up, 58.3% of PRK patients achieved 20/20 uncorrected vision. However, only 40.2% of patients who received astigmatic correction achieved 20/20 uncorrected vision. Although 93.7% of PRK patients achieved 20/40 or better uncorrected vision, only 86.6% achieved 20/40 with astigmatic correction.

While 0.2% of patients lost two lines or more of best spectacle corrected visual acuity 2 years after PRK, 8.5% of patients (or 4.8% if noncorneal losses and report errors are subtracted) who underwent astigmatic PRK did; however, only 2% of those who lost two or more lines related to laser treatment did not retain 20/20 vision.

The incidence of glare also was higher at first, Dr. Eydelman said, but all cases disappeared after 2 years. However, the incidence of night vision problems was higher for astigmatism, as were reports of bright lights and double vision.

Two panel members who were selected to comment on Visx's presentation disagreed whether the results for astigmatic correction were good enough to warrant FDA approval for the system.

Panel member Woodford Van Meter, MD, said he voted against approval because U.S. clinical trials had 2-year follow-up data on only three patients in the upper range of correction.

Panel member James P. McCulley, MD, said the variables involved mean that PRK for astigmatism is inherently more difficult, so the percentages of success and complications will not be as good. "The risk is acceptable and appropriate with informed consent by patients prior to the surgery," he said.

Panel members also cited two more issues that affected their decisions. Mark A. Bullimore, MCOptom, PhD, voted against approval over concerns about ablation diameter along the minor axis of correction, which can be as small as 4.24 mm. Data presented at the panel meeting suggested that patients with small ablation zones could expect more occurrences of glare or night vision problems due to the small ablation zone.

Once again, panel members who voted for approval agreed that the issues would be adequately addressed by informed consent of patients.

Panel members also cited concerns about the accuracy of measurement of the axis of residual astigmatism for small cylinders. However, Dr. McCulley said, the residual cylinder is typically of small magnitude — for example, 0.25D. It was also noted that accurate determination of astigmatism is more difficult for lesser degrees of astigmatism.

James Salz, MD, a paid Visx consultant from the University of Southern California in Los Angeles, explained the rotation in an interview after the meeting.

"The refractions of high cylinder [patients] are very accurate," he said. "You can outline the axis much more precisely, within a few degrees. But with small cylinders, there's a lot of variation in the preoperative measurements, so it's a lot less precise when you have 1 D or less of astigmatism."

U.K. researchers routinely correct as little as .25 D of astigmatism, Salz said. The attempt can be the difference between 20/20 vision and 20/40 vision.

Safety data presented

During the meeting, Dr. Salz told the panel that his research found no more complications than what normally occurs during PRK.

Overall, safety data from the Visx study compared well against FDA goals, Dr. Salz said. PRK for astigmatism matched or beat the FDA goals in five safety measures: losing two or more lines of best corrected visual acuity (BCVA), having BCVA better than 20/40, haze, induced astigmatism and induced adverse events.

For Your Information:
Marc Odrich, MD, practices at Columbia Presbyterian Eastside, 16 E. 60th Street, New York, NY; (888) CVC-1660. Dr. Odrich did not disclose whether or not he has a direct financial interest in the products mentioned in this article. He is a paid consultant for Visx.
A. Ralph Rosenthal, MD, and Malvina Eydelman, MD, can be reached at the Food and Drug Administration, Division of Ophthalmic Devices, 9200 Corporate Boulevard, Rockville, MD 20850; (301) 594-2205; fax: (301) 480-4201. Drs. Rosenthal and Eydelman did not disclose whether or not they have a direct financial interest in the products mentioned in this article or if they are paid consultants for any companies mentioned.
James Salz, MD, practices at Suite 390W, Cedars Sinai Medical, 8635 W. Third St., Los Angeles, CA 90048; (310) 652-1133; fax: (310) 657-1719; e-mail: jjsalzeye@aol.com. Dr. Salz has a direct financial interest in and is a paid consultant for Visx.
James P. McCulley, MD, practices at The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235-9057; (214) 648-3407; fax: (214) 648-2382. Dr. McCulley has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
Mark A. Bullimore, MCOptom, PhD, teaches at Ohio State University, 338 W. 10th Ave., Columbus, OH 43210; (614) 292-4724; fax: (614) 292-4949; e-mail: bullimore.1@osu.edu. Dr. Bullimore has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
Woodford Van Meter, MD, practices at Central Medical Plaza, 1760 Nicholasville Rd., Suite 203, Lexington, KY 90503; (606) 275-4001; fax: (606) 275-1142. Dr. Van Meter has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
Visxcan be contacted through Vince Powers at Dorland Sweeney Jones in Philadelphia, (215) 625-0111.