Neuroretinal rim width ratios in morphological glaucoma diagnosis

Abstract

Aims: To evaluate the inferior to temporal neuroretinal rim width ratio and superior to temporal rim width ratio as measures of rim shape for diagnosis of glaucoma.

Methods: Colour stereo optic disc photographs of 527 normal subjects, 100 ocular hypertensive individuals with normal visual fields, and 202 open angle glaucoma patients with a mean perimetric defect of less than 10 dB were morphometrically evaluated. Eyes with an optic cup area of < 0.2 mm2 were excluded.

Results: In the normal subjects, inferior to temporal rim width ratio (1.67 (SD 0.53)) was significantly (p < 0.0001) higher than superior to temporal rim width ratio (1.56 (0.49)). Both ratios were significantly (p < 0.0001) higher the more vertically the optic disc was configured. In the normal eyes, both ratios were statistically independent of disc size, rim area, refractive error, age, and sex. With the differences being more marked for the inferior to temporal ratio than for the superior to temporal ratio, both rim width ratios were significantly (p < 0.005) lower in the ocular hypertensive group than in the normal group. Despite the high significance of the differences, diagnostic power of the inferior ratio and the superior ratio was 59% and 58%, respectively, indicating a marked overlap between the groups.

Conclusions: Abnormally low inferior to temporal and superior to temporal rim width ratios can indicate glaucomatous optic nerve damage in some ocular hypertensive eyes. Being independent of optic disc size and ocular magnification, the rim width ratios may be taken as one among other variables for the ophthalmoscopic optic disc evaluation, taking into account, however, a pronounced overlap between normal eyes and ocular hypertensive eyes.

Figure 1

Photograph of an abnormally large, otherwise normal optic disc. Optic disc data: area, 5.7 mm²; neuroretinal rim width (arrows) inferior, 0.57 mm; superior, 0.35 mm; temporal, 0.18 mm; ratio of inferior to temporal rim width, 3.17; ratio of superior to temporal rim width, 1.94 . Note physiological shape of the neuroretinal rim.

Figure 2

Optic disc photograph of an ocular hypertensive eye without visual field defects. Optic disc data: area, 1.80 mm²; neuroretinal rim width (arrows) inferior, 0.37 mm; superior, 0.39 mm; temporal, 0.34 mm; ratio of inferior to temporal rim width, 1.09; ratio of superior to temporal rim width, 1.15 . Note abnormal shape of the neuroretinal rim.

Figure 3

Box plot showing the distribution of the inferior to temporal rim width ratio in the three study groups.

Figure 4

Box plot showing the distribution of the superior to temporal rim width ratio in the three study groups.