The Isnt Rule And The Modified Isnt Rule As A Screening Tool For Glaucoma With Myopic Tilted Disc

Abstract

Purpose: : To determine whether the ISNT rule (that normal eyes show a characteristic configuration for disc rim thickness of inferior≥superior≥nasal≥temporal) and the modified ISNT rule (application of ISNT rule based on the long axis of the disc) can differentiate glaucomatous eyes with myopic tilted disc from normal eyes.

Methods: : In this retrospective study, subjects who had myopic tilted disc underwent comprehensive ophthalmic examinations, including measurement of refractive error, axial length, stereoscopic disc photography, and simultaneous automated perimetry. Subjects with normal eyes had no evidence of glaucomatous optic neuropathy and had normal perimetry measurements. Subjects with glaucoma had a reproducible glaucomatous visual field defect. One eye from each subject was randomly enrolled. The ISNT rule which was based on the vertical and horizontal meridian was assessed at the 3, 6, 9, and 12 o’clock positions. The modified ISNT rule which was based on the long axis of the disc was also assessed in the same eyes.

Results: : Sixty-three subjects with glaucoma (patient group) and 86 with normal eyes (normal control group) were enrolled. The mean angle between the long axis of the disc and the vertical meridian was 24.01 ± 7.71 (8-69) degrees. The ISNT rule was violated in 46 subjects (73.0%) of patient group and 28 subjects (32.6%) of normal control group (p<0.001). The modified ISNT rule was violated in 57 subjects (90.5%) of patient group and 9 subjects (10.5%) of normal control group (p<0.001). In logistic regression analysis adjusting for age and axial length, the odds ratio for glaucoma associated with violation of the ISNT rule was 3.7 (95% confidence interval, 1.17-11.76) and the odds ratio for glaucoma associated with violation of the modified ISNT rule was 277.4 (95% confidence interval, 13.66-5634.60).

Conclusions: : The modified ISNT rule is useful in the screening of glaucoma with myopic tilted disc.

Keywords: optic disc