Ultrastructure of internal limiting membrane removed during plasmin-assisted vitrectomy from eyes with diabetic macular edema

Abstract

Purpose: To study the effect of autologous plasmin enzyme (APE) on the adhesion of the vitreous cortex to the internal limiting membrane (ILM) in eyes with diabetic macular edema.

Design: Nonrandomized, comparative, interventional case series.

Participants: Ten eyes of 10 patients with diabetic macular edema without a posterior vitreous detachment (PVD), which were treated with APE as an adjunct to conventional pars plana vitrectomy, and 10 eyes of 9 patients without a PVD, which underwent pars plana vitrectomy without APE, were studied.

Methods: In the APE group, 0.4 IU of APE was injected into the midvitreous cavity in 9 eyes, and 0.8 IU of APE in 1 eye. Thirty minutes after plasmin injection, the eyes underwent pars plana vitrectomy with ILM peeling. All eyes in the control group had conventional vitreous surgery with ILM peeling. The removed ILMs were investigated for the presence of vitreous and for ultrastructural differences by transmission and scanning electron microscopy.

Main outcome measures: The status of the vitreous and induction of a PVD during surgery, and the presence of vitreous and ultrastructural differences of the removed ILM by transmission and scanning electron microscopy.

Results: In APE-treated eyes, the degree of liquefaction of the vitreous was graded as high in 4 eyes. Spontaneous PVD occurred in 2 eyes, whereas core vitrectomy with a maximum vacuum of 100 mmHg induced a PVD in 2 additional eyes. In the control group, 8 eyes required suction with a maximum of 200 mmHg to induce the PVD. Scanning electron micrography of the removed ILM in the APE-treated eyes showed a smooth surface on the vitreous side in 8 eyes and only sparse collagen fibers in 2 eyes. Conversely, in the control group, dense vitreous fibers were found in 4 eyes, sparse collagen fibrils in 3 eyes, and a smooth retinal surface in 3 eyes.

Conclusions: These findings indicate that APE helps separate the vitreous hyaloid from the ILM surface and may be a useful adjunct to conventional vitreous surgery for diabetic macular edema.