Otago glaucoma surgery outcome study: electron microscopy of capsules around Molteno implants

PURPOSE. To report the ultrastructure of cells and extracellular matrix components in Molteno implant capsules examined by scanning and transmission electron microscopy.

Ultrastructural features including cytology, distribution of apoptotic cells, collagens, basement membranes, elastic fibrils, and glycoproteins were examined by scanning and transmission electron microscopy. Findings were correlated with the clinical features of 31 specimens of glaucomatous eyes treated with Molteno implants 0.3 to 14.9 years previously.

Capsules showed two layers: an outer, moderately cellular vascular layer of normal-appearing cells and collagen and an inner, avascular, hypocellular layer of altered cells and collagen. Cells included fibroblasts, myofibroblasts, and tissue histiocytes that showed features indicating metabolic activity, with swelling, vacuolation, and apoptosis, and the formation of numerous membrane-bound vesicles. These features, together with alteration and disintegration of extracellular matrix, increased with time after surgery.

The results support those in previous light microscopic studies and indicate that the normal life cycle of capsules in both primary and secondary glaucoma include continual outer surface renewal balanced by inner surface degeneration associated with apoptosis and breakdown of tissue matrix components which become more marked over time.