Histology of posterior scleral foramen in normal eyes: its possible role in optic nerve damage in chronic open angle glaucoma.

We examined the histologic features of the posterior scleral foramen in 27 enucleated eyes (16 during autopsy and 11 with choroidal malignant melanoma). The histologic findings of the posterior scleral foramen were similar to those in previous reports. The shape of the scleral foramen was either cylindrical or truncated, the latter occurring when the inner margin of the sclera projected with a crest-like edge pressing into the optic nerve. This configuration was encountered more frequently in the upper and lower temporal aspects of the scleral foramen in 10 eyes, while the nasal rim was free of such projection in all the eyes. We hypothesize that the effect of prolonged high intraocular pressure exerted on the axonal tissue against these crest-like edges of the non-distensible scleral foramen might be the major factor in the etiology of early arcuate nerve fiber bundle defects in primary open-angle glaucoma.