Effects on the RPE following choriocapillaris occlusion induced by laser targeted photo-occlusion and conventional photodynamic therapy

Purpose: Photodynamic therapy (PDT) is being evaluated as a method to non-thermally occlude choroidal neovascular membranes (CNVM), but it may not preserve RPE integrity. Our method, laser targeted photo-occlusion, might occlude CNVM selectively, while possibly preserving the RPE. The two methods were compared ultrastructurally in the rat Methods: An intravenously injected photosensitizer, encapsulated in heat sensitive liposomes, was locally released in the choriocapillaris of normal rats by causing a local mild rise of temperature with the aid of a non-coagulating argon laser beam. A diode laser (680 nm) was then used to activate the photosensitizer upon its release and cause vasoocclusion. Conventional PDT was performed by injecting the same photosensitizer in the non-encapsulated form. The threshold for choriocapillaris occlusion was confirmed in both techniques by laser targeted angiography. Histology was performed at 48 hours after both treatments. Results: Thrombi observed by electron microscopy confirmed the occlusion of the choriocapillaris with preservation of retinal vessels using both techniques. In animals treated by conventional PDT, the RPE was irreparably damaged with disruption of the cell membrane and intracellular organelles. In contrast, in animals treated by laser targeted photo-occlusion, the RPE cellular structure remained intact with preservation of nuclei. Subtle swelling of the mitochondria was the only electron microscopic change noted. Conclusion: Laser targeted photo-occlusion permits selective occlusion of the normal choriocapillaris without significant damage to the overlying RPE. The method thus has potential as a treatment of CNVM devoid of iatrogenic loss of vision.

Duke Scholars

Author Sanjay Girdhari Asrani Ophthalmology, Glaucoma