Clinicopathological correlation in exudative age related macular degeneration: histological differentiation between classic and occult choroidal neovascularisation

Aims-To analyse the histopathology of classic and occult choroidal neovascular membrane surgical specimens in age related macular degeneration. Methods-35 membranes, from a consecutive series of surgically removed choroidal neovascular membranes in age related macular degeneration, were classified as classic or occult following the guidelines of the Macular Photocoagulation Study. Membranes with classic as well as occult components were considered as mixed membranes. The membranes were serially sectioned and stained with haematoxylin and eosin, Masson trichrome, periodic acid-Schiff, and phosphotungstic acid haematoxylin stain. The correlation has been made in a masked fashion. Results-31 membranes (19 classic, 10 occult, and two mixed membranes) could be analysed histologically. 18 classic choroidal neovascular membranes had a major subretinal fibrovascular component and 10 of these had an additional, minor fibrovascular component under the retinal pigment epithelium. The 10 occult membranes contained a fibrovascular component under the retinal pigment epithelium and the two mixed membranes contained fibrovascular tissue on both sides of the retinal pigment epithelium. Fibrin and remains of outer segments tended to occur at the lateral edges of classic membranes and to cover the inner surface of occult membranes. Conclusion-Classic choroidal neovascularisation in age related macular degeneration is predominantly composed of subretinal fibrovascular tissue while occult choroidal neovascularisation is composed of fibrovascular tissue at the choroidal side of the retinal pigment epithelium.