Model of epithelial downgrowth: III. Scanning and transmission electron microscopy of iris epithelialization.

Epithelialization of uveal structures is frequently difficult to diagnose clinically and may require scanning and/or transmission electron microscopy to detect histologically. Since the scanning and transmission electron microscopic findings of progressive iris epithelialization have not previously been described, we examined a cat model of epithelial downgrowth for iris findings from 23 days through 4 months post-implantations of epithelium. Features associated with iris epithelialization included direct contact of iris with implanted epithelium, allowing initially rapid epithelialization of anterior iris structures, and slower epithelialization of posterior iris pigmented epithelium. The morphology of the migrating epithelium progressed from spindle shaped cells with small numbers of pseudopodia and microvillae to confluence of up to five layers of stratified epithelium with numerous surface microvilli. Anterior iris epithelial morphology consisted of cuboidal shaped cells with "looser" cell junctional interdigitations, versus a more squamous appearance of posterior iris epithelialization. A monolayer of lead cells or thin sheets of epithelium may be present well before a clinically apparent multicellular sheet of epithelium is seen.