Approach re-treatment for off-axis ablation in 2 stages

April 1, 2007

Las Vegas-Off-axis ablations are rare with wavefront-guided LASIK procedures but still occur with conventional treatment. Although the consequences can be severe, good results eventually can be achieved through appropriate management strategies, said Robert K. Maloney, MD, speaking here during Refractive Surgery Subspecialty Day at the American Academy of Ophthalmology annual meeting.

Dr. Maloney, director of the Maloney Vision Institute in Los Angeles, used a case report to illustrate the recommended treatment approach in response to ablation errors.

He described a case involving a 23-year-old male with simple, myopic astigmatism who wanted to undergo LASIK (OD: –0.37 –4.62 × 08 –20/20; OS: –0.62 –4.75 × 166 –20/20). His cylinder reading put him outside of the range of custom ablation, in which it is nearly impossible to do an erroneous off-axis ablation, so he was scheduled to undergo conventional LASIK.

"This is a typical error; a digit is dropped or added," Dr. Maloney said. "It's typically 90° away where the axis error occurs, which maximizes the induced astigmatism."

As expected as a result of this error, the patient's astigmatism had doubled from 4.62 to 9.5 D at a 2-week postoperative visit. His best-corrected visual acuity, however, was 20/20.

At 2.5 months postoperatively, the spherical equivalent was perfect, but considerable residual astigmatism remained, although it had regressed slightly. The cylinder was less than double the preoperative level.

"There was some regression in cylinder between 2 weeks and 3 months. For some patients, this may be a reason to avoid early re-treatment," Dr. Maloney said. "That's a temptation because you're pretty much horrified when it happens, but it's important to wait."

Dr. Maloney subsequently performed a conventional enhancement on the right eye at the same time that he performed LASIK on the left eye.

At 1 year, the right eye was doing well, given initial results of the surgery, and visual acuity was 20/20 (+2.37 –2.25 × 178); however, the patient remained highly dissatisfied.

Results in the left eye were perfect.

The next step was wavefront analysis and wavefront treatment. In the wavefront analysis, the highest aberration was the Zernike 4,2 term.

"This is the typical term you get in these off-axis or conventional cylinder ablations. It's very common, and it's because you essentially have a cylinder etched on the cornea," Dr. Maloney said.

The patient then underwent wavefront-guided re-treatment to eliminate the astigmatism in his right eye. "Remarkably, 3 months later, the patient thought his right eye was better than his left eye," Dr. Maloney added.

Refractive error was emmetropic in the right eye, and the left eye remained stable. Best-corrected vision in the right eye was 20/15, better than the 20/20 in the contralateral eye. On the final wavefronts, the patient had a lower root mean square error in the affected right eye (0.66) than in the left eye (0.74).

Lessons learned

Although this is only a case report, lessons can be drawn from it, Dr. Maloney said.

"One is that the initial cylinder increase does partially regress, so it may be worth waiting before re-treatment," he said.