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

To examine the association of optic disk ovality with myopic refractive error, axial length, and the visual field.

Prospective observational case series.

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 < or = 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.

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).

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.