Customized ablation with large optical zones advantageous

August 15, 2004

San Diego-In eyes treated with the Zyoptix Customized Ablation System (Bausch & Lomb, Rochester, NY), outcomes analysis demonstrated improvements in contrast sensitivity and higher-order aberrations in eyes treated with large optical zones of 6.5 to 7 mm and in those that had greater higher-order aberrations before treatment.

Scott MacRae, MD, reported the results from the FDA clinical trial at the American Society of Cataract and Refractive Surgery annual meeting.

A total of 340 eyes of 190 patients underwent custom ablation. The average preoperative myopia was –3.3 D and sphere –0.67 D. Every eye was included in the analysis. All patients were followed for 6 months after treatment.

Using a wavefront aperture diameter of 6 mm and considering the optical zone sizes of 6, 6.5, and 7 mm in a stratified group of patients with –4 to –5 D of myopia, the investigators sought to determine if the better results they obtained were influenced by the tendency to treat low myopia with large optical zones and higher myopia with smaller optical zones or if the optical zone is itself responsible, Dr. MacRae said.

Analysis of 4- to 5-D myopia showed that "the higher-order aberration increased more in the patients with the 6-mm optical zone than in patients with the 6.5-mm optical zone. There was almost no increase in higher-order aberrations in the patients with a 7-mm ablation optical zone," he added.

Improved contrast sensitivity "The greatest gain in customized correction was in improved contrast sensitivity, especially under low-light conditions such as during night driving, and not in visual acuity. The fixation that we as ophthalmologists have on visual acuity needs to shift toward an evaluation of factors such as contrast and night driving," he emphasized.

When the investigators evaluated contrast sensitivity, they found a good correlation between a gain in contrast sensitivity and minimization of a change in higher-order aberration.

"If there was very little increase in higher-order aberration, there was likely to be an improvement in contrast sensitivity. Twenty-four percent of eyes had a two-patch gain in contrast sensitivity, whereas only 2% of eyes had a two-patch loss of contrast sensitivity in this study. Patients were 10 times more likely to have a two-patch gain in contrast sensitivity that was associated with a reduction in higher-order aberration," he said.

When the preoperative higher-order aberration was compared with the gain in contrast sensitivity, there was a similar pattern in that if the eyes had more higher-order aberration, the gain tended to be greater; conversely, if the eyes had less higher-order aberration, there was no change in most patients, but they were less likely to have an increase in contrast sensitivity. However, the entire group was five times more likely to gain contrast sensitivity than to experience a loss.

"In both photopic and mesopic conditions, there was a one-patch improvement in contrast sensitivity for the entire study population, which is about a 29% improvement in contrast sensitivity at all five spatial frequencies tested [1.5, 3, 6, 12, and 18 cycles per degree]," Dr. MacRae said. In terms of the patient, this outcome indicated that the patient was four times as likely to notice an improvement in night driving.

High patient satisfaction Patient satisfaction was high following the procedure-98% of patients expressed either moderate satisfaction or were very satisfied.