Abstract
Abstract: :
Purpose: To examine the association of optic disc tilt with myopic refractive error and axial length, and to investigate the effect of optic disc tilt on visual field performance, as assessed by automated threshold perimetry. Methods: 150 myopic male recruits were enrolled in the study. In one randomly selected eye, subjective refraction, slit lamp examination, applanation tonometry, gonioscopy, a–scan ultrasonography, fundoscopy and colour optic disc stereo photography were performed. The degree of optic disc tilt was assessed by calculating the ratio of minimum to maximum disc diameter (tilt ratio). A ratio of less than 0.8 was taken to signify significant optic disc tilt. Visual fields were tested using static automated threshold perimetry with 2 methods of optical correction, trial lenses and contact lenses. Inter–observer error with assessed with the Bland Altman technique. Statistical testing was performed using Pearson correlation and linear regression analysis. Results: 137 subjects completed the study. The mean age was 21.2 ± 1.1 yrs, and mean spherical equivalent was –6.36 ± 3.56 dioptres (range: –0.25 to –14.75 dioptres). The mean tilt ratio was 0.83 ± 0.09, and 55 subjects (40.2%) had significant tilted optic discs. Greater optic disc tilt (smaller tilt ratio) was correlated with higher spherical equivalent (p=0.009) and a longer axial length (p=0.009). The majority of subjects (95.6%) had normal visual fields with both methods of optical correction. Using linear regression analysis, increasing spherical equivalent and smaller tilt ratio were independently related to a higher mean defect. Conclusion: Increased optic disc tilt was associated with increasing myopia and reduced sensitivity on visual field testing. These factors should be taken into consideration in the assessment of glaucoma in myopes.
Keywords: myopia • visual fields • optic disc