[Selective occlusion of subretinal neovascularization with photodynamic therapy]

Conventional photocoagulation of subretinal membranes induces a non-selective thermal necrosis of retinal and choroidal layers with extensive collateral damage. Hence, this modality is of limited value for the treatment of lesions close to or underneath the fovea. Photodynamic therapy uses systemic administration of a primarily non-toxic photosensitizer with localized light activation of the dye by subthermal light intensities. It provides intraluminal vascular occlusion by means of localized endothelial damage. Enhanced selectivity for neovascularization is achieved by the use of carrier molecules with increased receptor density on proliferating endothelial cells, e.g. low-density lipoproteins (LDL). Benzoporphyrin derivative (BPD), currently in phase I clinical trials, was complexed with LDL. BPD-LDL was used for photodynamic occlusion of the choriocapillary layer in the rabbit model. Subretinal photothrombosis and collateral damage to neural retina, retinal pigment epithelium, Bruch's membrane and large choroidal vessels were documented by ophthalmoscopy, angiography and light and electron microscopic histology. Homogenous vascular occlusion without retinal destruction was induced with light doses as low as 10 J/cm2. Selective neovascular occlusion by photodynamic therapy may allow occlusion of subretinal membranes while preserving retinal integrity and visual function.