Internal limiting membrane peeling stimulates macular hole closure, surgeon says

The surgical trauma induced by ILM dissection provides the stimulus to redirect glial proliferation to counteract tangential forces.

TAORMINA, Italy — Peeling of the internal limiting membrane is not essential for anatomic or visual success in macular hole surgery, but may be a standardizable means of inducing therapeutic glial proliferation.

“There are contrasting opinions on the value of internal limiting membrane (ILM) peeling in macular hole surgery,” said William E. Smiddy, MD, of the University of Miami, here at the Jules Gonin Club meeting. “Some suggest that it is a decisive factor for the anatomic and visual success of the treatment. Others show evidence that the results of case series treated before ILM peeling are comparable to those more recently obtained using the technique.”

“In our study, we evaluated the ability to peel ILM and epiretinal membranes and correlated the extent of membrane peeling and other intraoperative features to anatomic and functional success,” Dr. Smiddy said.

A total of 193 eyes of 183 consecutive patients were treated with macular hole surgery. ILM peeling was attempted in all eyes.

“In 44 eyes (23%) we achieved a complete peeling of the internal limiting membrane around the edge of the hole. In 83 eyes (43%) we could only peel it partially and in 66 eyes (34%) we dissected the membrane but could not identify the edge and peel it,” Dr. Smiddy said. No significant correlation was found between the degree of ILM peeling and preoperative factors, such as stage of the hole and visual acuity.

“We achieved a high rate of anatomic success in all cases, but the highest percentage (99%; P=0.080) was achieved in the eyes with ILM dissection only. On the contrary, final visual acuity of 20/50 or better was better in eyes with more complete ILM peeling (P=0.045),” he reported.

Stimulus to glial proliferation

The results of the study seemed to corroborate the supposition that ILM peeling is not a critical factor for anatomic success. The highest rate of macular hole closure was in fact obtained in the eyes where the membrane was dissected, but not peeled.

“We cannot say, however, that our unsuccessful peeling maneuver is comparable to a ‘no-touch’ technique, where ILM peeling is not even attempted. Although it is only a supposition, because there was no control group in our study, I believe the dissection of the membrane played an important role in the process of hole closure,” Dr. Smiddy said.

Although the possible role of ILM in the pathogenesis of macular holes is uncertain, there is general agreement that the contractile forces generated by glial cells migrating to the inner ILM surface progressively enlarge the macular hole. The rationale for ILM peeling is to contrast this process by removing the template on which the glial tissue proliferates and contracts.

“On the other hand, there is evidence that the same contractile forces that enlarge the macular hole can be counteracted or redirected to induce reapproximation of foveal elements and macular hole closure,” Dr. Smiddy added. “There are good reasons to believe that the surgical trauma induced by ILM dissection, whether it is met with complete, partial or no ILM removal, provides the stimulus to redirect glial proliferation to counteract the tangential forces. Since the ILM is composed of the footplates of Mueller cells, shearing the cells may injure the cells and stimulate therapeutic glial proliferation. The higher anatomic success in this study with ILM dissection may only be due to a higher degree of tissue injury and stimulus to proliferation, resulting from our persistence at trying to lift the ILM edge,” he said.

According to Dr. Smiddy, the lesser degree of visual acuity increase in eyes with ILM dissection only could also be related to the effects of the surgical maneuvers.

“All our unsuccessful attempts to identify and peel the membrane may have produced some damage to inner retinal elements, resulting in lower visual success. Surely this could be overcome by improving our technique and using more effective surgical instruments, so that glial stimulation can be optimized, without producing unwanted damage to the surrounding structures,” he said.

For Your Information:

• William E. Smiddy, MD, can be reached at P.O. Box 016880, Miami, FL 33101-6880; (305) 326-6172; fax: (305) 326-6417; e-mail: wsmiddy@med.miami.edu.