Optic disc shape in glaucoma

Background: This study was performed to evaluate the shape of the optic disc in glaucoma. Methods: We examined morphometrically color stereo optic disc photographs of patients with primary open-angle glaucoma (n=804), secondary open-angle glaucoma (n=130), normal-pressure glaucoma (n=75), and high myopia combined with open-angle glaucoma (n=33), visually normal subjects (n=421), and nonglaucomatous subjects with high myopia (n=36). The optic disc form was determined by the ratio of the minimal to the maximal disc diameter, the ratio of the horizontal to the vertical disc diameter, the angle between the maximal diameter and the horizontal, and a calculated form factor. Results: In the normal eyes, the ratios and the form factor varied interindividually by less than 1:2. For a myopic refractive error of less than -8 D, the normal eyes and the glaucoma eyes did not differ significantly (P>0.20) in their slightly vertically oval optic disc shape. Within the primary open-angle glaucoma group, the optic disc shape was not correlated with the neuroretinal rim area and the mean perimetric defect, either interindividually or in an intraindividual bilateral comparison. In the highly myopic group, the optic disc was significantly more ovally configurated, more obliquely orientated, and larger than in any other group. Conclusions: In contrast to the size of the optic nerve head, the shape of the optic disc does not show pronounced interindividual variability in eyes with a myopic refractive error of less than -8 D. With highly myopic eyes excluded, the optic disc shape as single variable is not markedly important for pathogenesis, early diagnosis and differential diagnosis of the glaucomas.