Innovation Spotlight - LASIK Results

Studying first-eye LASIK results helps planning of second-eye treatment

By Lynda Charters
Reviewed by Peter S. Hersh, MD

Newark, NJ-Performing bilateral sequential LASIK treatments about 1 week apart may produce a refractive outcome that is closer to emmetropia in the second eye, according to Peter S. Hersh, MD, who analyzed the utility of using first-eye results to predict second-eye outcome after LASIK.

Bilateral simultaneous LASIK treatment is gaining in popularity; the convenience and early binocularity between the two eyes is well appreciated by patients.

The risks include the rare occurrence of bilateral infection, epithelial downgrowth, irregular astigmatism, and bilateral flap complications, Dr. Hersh said.

In this study, Dr. Hersh and colleague Peter Chiang, MD, evaluated another potential outcome difference between sequential and simultaneous LASIK treatments: refractive predictability in individual patients. Although Dr. Hersh noted that little difference in refractive predictability has been found in previous population studies, they sought to determine if a more advantageous refractive outcome for individual patients could be achieved, and refractive outliers avoided, using sequential rather than simultaneous procedures.

"We compared the refractive predictability of LASIK between eyes in individuals to determine if the refractive results in the first eye that underwent surgery would be useful to predict the outcome of the second eye," said Dr. Hersh, chief of corneal and refractive surgery, department of ophthalmology, UMD-New Jersey Medical School, Newark, and director, Cornea and Laser Eye Institute, Hackensack University Medical Center, Teaneck, NJ.

Dr. Hersh and colleagues performed sequential bilateral LASIK in 196 eyes of 98 patients with a mean of 11.6 days between treatments. The Summit Apex excimer laser (Waltham, MA) was used in all procedures.

The preoperative refractive errors ranged from 2.3 to -12 D. Patients were excluded from analysis if they had only one eye treated and if they underwent any enhancements during the course of the study.

Paired predictability found

"We first wanted to look at the between-eye correlation of refractive predictability (the achieved minus the attempted correction) at 1 week, 1 month, and 3 months after surgery," Dr. Hersh said. "We then looked at any undercorrections or overcorrections that occurred in the first eye that underwent surgery and used this number to adjust our nomogram theoretically for the second eye.

"We then analyzed this outcome versus the actual outcome in the second eye at 1 week, 1 month, and 3 months after surgery to determine if the refractive result in the second eye could have been improved using the first-eye result," Dr. Hersh explained.

He reported that they found a good correlation and no difference in predictability between eye 1 and eye 2. If the patient had undercorrection during the surgery on the first eye, undercorrection was likely using the same nomogram in the second eye; likewise, if the first eye was overcorrected, the same was likely to occur in the second eye.

Waiting improved predictions

"With the knowledge that eye 1 was correlated with eye 2 in individual patients, we then compared the actual postoperative refractive outcome with the theoretical outcome if we had taken the first eye into account," he said.

"At all follow-up times, we found that the refractive results using our theoretical treatment based on first-eye outcome were better in the second eye at all time points compared with the actual result in which the first-eye treatment was not used," Dr. Hersh said.

When they performed this analysis with the data obtained from just the 1-week follow-up to adjust the correction for the second eye, they found the same results, he said.

This method of predicting the outcome was particularly effective for patients with lower degrees of myopia (less than 5.5 D) compared with those with higher myopia (p = 0.03).

Using 3-month theoretical refractive results, "when we looked at actual versus theoretical outcomes, 93% of eyes in the proposed attempted correction group, theoretically, would have fallen within 1 D of emmetropia, compared with 80% in the actual outcomes group," he said.

Dr. Hersh concluded that there appears to be good correlation of refractive predictability between each eye in a given patient following LASIK.

"A surgeon may be able to achieve correction closer to emmetropia in the second eye by applying the refractive results from the first eye," he said.

"Waiting 1 week between treatments of the first and second eyes was found to be potentially as effective as waiting a longer period," he added.

"The clinical significance of these findings remains unclear, but perhaps the number of refractive outliers with substantial bilateral overcorrection or undercorrection may be decreased, as well as the number of enhancements needed among LASIK patients," he suggested.

Dr. Hersh has no proprietary interest in any aspect of this study.

Ophthalmology Times / APRIL 15, 2000