Aim: To investigate effects of photodynamic therapy (PDT) on human choroidal neovascularisation (CNV).
Methods: Two patients with recurrences after PDT with verteporfin underwent surgical extraction of the CNV. Immediately after surgical excision the subfoveal neovascular membranes were divided for light microscopic and for electron microscopic processing. For light microscopy tissues were embedded in paraffin. Sections were stained with haematoxylin and eosin, and the periodic acid Schiff (PAS) reaction was performed to determine histological diagnosis and to ensure tissue quality. For electron microscopy the specimens were fixed in glutaraldehyde and embedded in epoxy resin. Semithin sections were stained with uranyl acetate and lead citrate and examined with a transmission electron microscope.
Results: Light microscopy showed thick fibrovascular membranes in both cases. On the outer surface remnants of retinal pigment epithelial cells resting on thickened inner aspect of Bruch's membrane were found. On the retinal side some outer segments were found. The membrane showed areas with irregularly shaped vessels. Electron photomicrographs showed occluded vessels within the CNV containing thrombotic masses and/or ultrastructural damage of the neovascular endothelium. Most of the vessels presented regressive changes with vacuolisation and fragmentation of the neovascular endothelium accompanied by disintegration of the endothelial cell layer. Extravasation of red blood cells was observed. Occasionally, vessels with normal endothelium containing intact red blood cells were observed. Some vessels contained immature endothelial cells. At some locations the retinal pigment epithelium cells (RPE) were metaplastic showing highly vacuolised cytoplasm.
Conclusions: These findings suggest that the evidence of fluorescein leakage from the CNV and enlargement of the neovascular complex following PDT could be related to new vessel growth and recanalisation of occluded vessels. Additionally, RPE disturbances were observed in the specimens. This finding may be related to the original pathology or could indicate that PDT treatment may result in RPE atrophy.