Effect of photocoagulation on the barrier function of the pigment epithelium. II. A study by electron microscopy.

The healing of retinal photocoagulation burns and their permeability to colloidal carbon and horseradish peroxidase was studied by electron microscopy. Recent burns showed disruption of intercellular junctions in the pigment epithelium. By 2 days there was infiltration of the burn by proliferating pigment epithelial cells, and by 7 days the burn was composed of a mass of interconnected cells of pigment epithelial and Müller cell origin. Fresh photocoagulation burns result in complete disruption of the blood-ocular barrier, permitting particles as large as colloidal carbon to pass between disrupted pigment epithelial cells. Healed photocoagulation burns remain permeable to smaller tracers such as horseradish peroxidase.