Optic disc morphology in myopic primary open-angle glaucoma

Objective: To evaluate the morphology of the optic disc in highly myopic eyes with primary open-angle glaucoma. Methods: Color stereo optic disc photographs of 44 patients with primary open-angle glaucoma and a myopic refractive error exceeding –8 diopters were morphometrically examined and compared with disc photographs of 571 patients with primary open-angle glaucoma and a myopic refractive error of less than –8 diopters. Results: In the highly myopic group, compared to the control group, the optic disc was significantly (P<0.0001) larger, the disc shape was significantly (P<0.0005) more elongated, and the optic cup depth was significantly (P<0.0001) more shallow. The loss of neuroretinal rim was more concentric, and localized retinal nerve fiber layer defects were found significantly less frequently in the highly myopic group than in the control group. In the highly myopic group, zone beta of parapapillary atrophy was significantly (P<0.0001) larger. Conclusion: The optic disc morphology in primary open-angle glaucoma differs significantly between highly myopic eyes and eyes with hyperopia or low to moderate myopia. The highly myopic eyes are characterized by secondary macrodiscs with elongated shape, shallow and concentric disc cupping, large parapapillary atrophy, and low frequency of localized retinal nerve fiber layer defects. Glaucomatous optic nerve damage in highly myopic eyes, compared to eyes with a normal refractive error, is more diffuse than localized.