RETINAL AND CHOROIDAL RESPONSES TO PANRETINAL PHOTOCOAGULATION - AN ULTRASTRUCTURAL PERSPECTIVE

Background: There have been few histological or ultrastructural studie s of the outer retina and choriocapillaris following panretinal photoc oagulation therapy. This investigation examines the long-term morpholo gical effects of panretinal photocoagulation in two patients with type II diabetes who had received laser treatment more than 6 months prior to death. Methods: Regions of retina and choroid from each patient we re fixed in 2.5% glutaraldehyde, dissected out and examined using ligh t microscopy and scanning and transmission electron microscopy. Result s: After removing the neural retina, scanning electron microscopy of n on-photocoagulated areas of the eye cups revealed normal cobblestone-l ike retinal pigment epithelial (RPE) cells. Regions with laser scars s howed little RPE infiltration into the scar area, although large round ed cells often appeared in isolation within these areas. Sections of t he retina and choroid in burn regions showed a complete absence of the outer nuclear layer and photoreceptor cells, with the inner retinal l ayers lying in close apposition to Bruch's membrane. Non-photocoagulat ed regions of the retina and choroid appeared normal in terms of both cell number and cell distribution. The RPE layer was absent within bur n scars but many RPE-like cells appeared markedly hypertrophic at the edges of these regions. Bruch's membrane always remained intact, altho ugh the underlying choriocapillaris was clearly disrupted at the point of photocoagulation burns, appearing largely fibrosed and nonperfused . Occasional choroidal capillaries occurring in this region were typic ally small in profile and had plump non-fenestrated endothelium. Concl usions: This study outlines retinal and choroidal cell responses to pa nretinal photocoagulation in diabetic patients and demonstrates an app arent reduction in the capacity of these tissues to repair laser damag e.