research digest

Corneal Reinnervation 3 Years after LASIK

A study conducted at the Mayo Clinic College of Medicine in Rochester, Minn., and published in the November issue of Investigative Ophthalmology & Visual Science, used confocal microscopy to examine 17 corneas of 11 patients who had undergone LASIK for myopia from -2D to -11D. In these patients it was found that after LASIK, both the subbasal and stromal nerves in the corneal flap recovered slowly. It was also found that the subbasal and stromal nerves did not return to their preoperative densities by 3 years postoperatively, and that after an initial return to near-preoperative levels, the subbasal nerves appeared to decrease in number and density again between 2 and 3 years after LASIK.

Patients were examined prior to surgery, and at 1, 3, 6, 12, 24, and 36 months after surgery. The number and density of subbasal nerves decreased by more than 90% in the first month after surgery. These nerves began to recover by 6 months post-op, and by 2 years had reached a level not notably different from preoperative levels. However, between the second and third years post-op, the number and density decreased again, and by the third year density was less than 60% of pre-LASIK levels.

Researchers found that in the stromal flap most nerve fiber bundles were lost after LASIK, but began to recover by the third month. In later patient examinations it was found that by month 36 these fibers had not reached their original numbers. Researchers did not find any noteworthy changes in nerve number or density in the stromal bed posterior to the LASIK flap interface.

Ophthalmology Management asked Marguerite McDonald, M.D., clinical professor of ophthalmology at Tulane University School of Medicine to comment on the findings. "This study further reinforces the decision made by many surgeons, including myself, to switch back to 100% surface ablation," she said. "One reason for our switch is that dry eyes are made significantly worse by LASIK, especially in older patients. LASIK is very successful in the vast majority of patients, but this study should help us to weed out -- in advance -- those patients who cannot safely undergo the reduction in corneal nerve population caused by LASIK. This study should also influence LASIK surgeons to more readily consider surface ablation (PRK, LASEK, or epi-LASIK) in older patients and any patient with the signs and/or symptoms of dry eye disease."

Two Artificial Tears Studied with Restasis

A 6-month, concurrently controlled, randomized, investigator-masked, multisite clinical trial evaluated the effectiveness of two kinds of artificial tears when used as supportive therapy to cyclosporine ophthalmic emulsion 0.05% (Restasis). The results of the trial were presented at the 4th International Conference on the Lacrimal Gland, Tear Film, Ocular Surface, and Dry Eye Syndromes: Basic Science and Clinical Relevance, which was held in Fajardo, Puerto Rico, in November 2004.

The trial evaluated 61 adults who had a diagnosis of dry eye. To qualify for this trial patients had to have a corneal staining score >=3 (NEI grid), Schirmer test results without anesthesia of ¾7 mm, and had to express the need for artificial tears at least some of the time.

Patients were randomized into three treatment groups. Group 1 received Restasis b.i.d. with Systane at least once a day as supportive therapy. Group 2 received Restasis b.i.d. with Refresh Tears at least once a day as supportive therapy. Group 3 received Systane alone q.i.d. Signs and symptoms were measured at 7 days prior to baseline and at days 0, 7, 14, 28, 42, 120, and 180.

Investigators concluded that Systane combined with Restasis was superior to Restasis combined with Refresh Tears in reducing dry eye symptoms. Less burning, stinging, grittiness, dryness, and frequent scratchiness was observed in the Systane plus Restasis group.

Systane alone demonstrated significantly less frequent burning, dryness, and scratchiness than the Restasis plus Refresh Tears group. No statistically significant differences were seen between the Systane and Restasis group and Systane alone.

Ophthalmology Management asked Kenneth Sall, M.D., an investigator on the study to comment on the findings. He said, "this study showed that Restasis plus Systane was superior to Restasis plus Refresh in alleviating the signs and symptoms of dry eye."