Optic disk ovality as an index of tilt and its relationship to myopia and perimetry

PURPOSE: To examine the association of optic disk ovality with myopic refractive error, axial length, and the visual field. DESIGN: Prospective observational case series. METHODS: The study included 150 randomly recruited male subjects with myopia. In all cases, one eye was randomly selected, and subjective refraction, slit-lamp examination, applanation tonometry, gonioscopy, A-scan ultrasonography, funduscopy, and color optic disk stereo photography were performed. Disk ovality was assessed using the ratio of minimum to maximum disk diameter (index of tilt). A ratio of less than or equal to 0.8 was considered as significant disk tilt. Visual fields were tested using static automated threshold perimetry with two methods of optical correction: trial lenses and contact lenses. RESULTS: Of the total sample, 137 subjects completed the study. Mean age was 21.2 +/- 1.1 year, and mean spherical equivalent was -6.36 +/- 3.56 diopters. Mean ovality ratio was 0.83 +/- 0.09; 55 subjects (40.2%) had significant tilted optic disks. Greater optic disk ovality (tilt) correlated with greater myopia (P =.009) and longer axial length (P =.009); 95.6% of subjects had normal visual fields with both methods of optical correction. Using multiple linear regression analysis, greater tilt was independently related to a higher mean defect on testing with trial lenses (P <.01). CONCLUSIONS: Increased optic disk tilt was associated with higher myopia and reduced sensitivity on field testing. These factors are important in the assessment of glaucoma in patients with myopia.