The ISNT Rule and Differentiation of Normal From Glaucomatous Eyes

Abstract

To determine whether the ISNT rule (that normal eyes show a characteristic configuration for disc rim thickness of inferiorՆsuperiorՆnasalՆtemporal), widely used for clinical evaluation of the optic nerve head, can differentiate normal from glaucomatous eyes.Methods: All subjects underwent complete eye examination, including achromatic automated perimetry, simultaneous stereoscopic disc photography, and confocal scanning laser ophthalmoscopy. Subjects with normal eyes had no evidence of glaucoma or ocular hypertension and had normal perimetry measurements. Subjects with glaucoma had a reproducible visual field defect. One eye from each subject was randomly enrolled. The ISNT rule was assessed by masked evaluation of disc photographs at the 3, 6, 9, and 12 o'clock positions.Results: Sixty-six subjects with normal eyes (33 black and 33 white individuals) and 43 with open-angle glaucoma (15 black and 28 white individuals) were enrolled. The ISNT rule was intact in 52 (79%) of 66 normal eyes and 12 (28%) of 43 glaucomatous eyes (PϽ.001). Multiple logistic regression indicated that the odds ratio for glaucoma associated with violation of the ISNT rule was 6.04 (95% confidence interval, 1.74-20.95) after adjustment for age; race was not a confounder of this association. Conclusion:The ISNT rule is useful in differentiating normal from glaucomatous optic nerves and is unaffected by race.

Automatic extraction of retinal features from colour retinal images for glaucoma diagnosis: A review

“…In case of Glaucoma, the Neuroretinal Rim disobeys the earlier mentioned rule. Although this is not the case with all Glaucoma patients [9], it is still a useful clinical method to aid in diagnosing Glaucoma. For the left eye, the position of Temporal and Nasal region will swap each other.…”

Different Clinical Parameters to Diagnose Glaucoma Disease: A Review

“…The ISNT rule is useful in the classification of normal and glaucomatous optic nerves [14]. In normal eye, the thickness of neural retinal rim changes from one sector to another and generally obeys the ISNT rule.…”

Optic nerve head segmentation using fundus images and optical coherence tomography images for glaucoma detection

“…Hence, the CDR is one of the features used to detect glaucoma. In addition to CDR, a parameter called the ISNT ratio which is the ratio of the sum of the blood vessels in the Inferior and the Superior regions to the sum of the blood vessels in the Nasal and the Temporal region is used 2 .The same parameter is also used based on the neuron retinal rim area. In OCT, the cup region will show features related to glaucoma.…”