Optic Disc Shape, Corneal Astigmatism, and Amblyopia

Objective: The cornea and the optic disc form the anteroposterior opening of the sclera. This study evaluated whether an abnormal shape of the optic disc is associated with an abnormal configuration of the cornea measured as corneal astigmatism. Design: The study design was a cross-sectional one. Participants: The study included 882 subjects (430 women, 452 men) with a mean age of 45.9 ± 13.6 years (mean ± standard deviation; range, 8–87 years) and a mean refractive error of −1.09 ± 2.76 diopters (range, −21.0 diopters to +7.0 diopters). Intervention: Corneal astigmatism was determined by keratometry, and the optic disc was analyzed morphometrically by planimetric evaluation of optic disc photographs. Main Outcome Measures: Corneal astigmatism, ratio of minimal-to-maximal disc diameter, and optic disc form factor were measured. Results: The amount of corneal astigmatism was significantly (P < 0.001) correlated with an increasingly elongated optic disc shape. Corneal astigmatism was significantly (P < 0.01) higher in eyes with tilted discs. It was significantly (P = 0.006) smaller in eyes with an almost circular disc shape. Amblyopia was significantly (P < 0.05) associated with an elongated optic disc shape and high corneal astigmatism. The axis of corneal astigmatism was correlated with the orientation of the longest disc diameter. The optic disc was significantly (P < 0.05; chi-square test) more often horizontally oval in eyes with a steeper horizontal corneal meridian than in eyes with a steeper vertical corneal meridian. Correspondingly, the disc was significantly (P < 0.05) more often vertically oval in eyes with a steeper vertical corneal meridian than in eyes with a steeper horizontal corneal meridian. Conclusions: An abnormal optic disc shape is significantly correlated with corneal astigmatism. Especially in young children, if an abnormal optic disc shape is found on routine ophthalmoscopy, refractometry should be performed to rule out corneal astigmatism and to prevent amblyopia. The direction of the longest optic disc diameter can indicate the axis of corneal astigmatism.