Histology of myopic posterior scleral staphylomas.

Abstract

Since histomorphometric descriptions of posterior scleral staphylomas, although forming a major part of myopic maculopathy, have been scarce so far, we histomorphometrically examined scleral staphylomas in enucleated human eyes. Using light microscopy, we histomorphometrically examined sagittal histological sections of human globes enucleated due to malignant choroidal melanomas or secondary angle-closure glaucoma. Out of 246 globes included into the study, posterior scleral staphylomas were detected in 10 eyes (mean length: 31.4±3.0mm; range: 28.0-37.0mm). In the staphylomatous region in the study group as compared with the corresponding region of a control group adjusted for age and axial length, scleral thickness was significantly lower (109±25µm versus 319±161µm; p=0.001). The study group in the staphylomatous region as compared to the highly myopic control group in the corresponding region did not differ significantly in retinal pigment epithelium (RPE) cell density (19.6±4.9 cells/300µm versus 21.1±5.7 cells/300µm; p=0.84) and RPE height (8.2±2.8µm versus 6.1±2.5µm; p=0.13), Bruch's membrane (BM) thickness (3.5±1.3µm versus 4.2±2.3µm; p=0.40) and choriocapillaris thickness (5.3±2.8µm versus 4.4±2.8µm; p=0.49) and density (164±99µm versus 226±38µm; p=0.13). All staphylomatous regions showed a localized BM defect. Marked scleral thinning and spatially correlated BM defects histologically characterized myopic scleral staphylomas, while thickness and density of the choriocapillaris and RPE and BM thickness did not differ significantly between staphylomatous versus non-staphylomatous eyes in the respective regions. These findings support the notion that a locally reduced scleral resistance against a backward pushing BM led to a local scleral outpouching. The outpouching-associated increase in curvature length may stretch BM with the sequel of a localized BM rupture.