Does the ISNT Rule Apply to the Retinal Nerve Fiber Layer?

Abstract

A larger number of normal eyes obeyed the IST rule compared with the ISNT rule for the RNFL thickness measured by HRT and OCT. Exclusion of the nasal sector from the analysis (IST rule) marginally improved the specificity in diagnosing glaucoma at the cost of the sensitivity, making neither of these parameters (ISNT and IST) likely to be useful clinically.

Applicability of ISNT and IST rules to the retinal nerve fibre layer using spectral domain optical coherence tomography in early glaucoma

“…The percentage of eyes following the ISNT rule was 55% (44 eyes) and 36.84% (28 eyes) in the normal group and the early glaucoma group, respectively (p=0.02). Pradhan et al 15 in their study on the stratus OCT showed that the ISNT rule on RNFL was applicable to 47.1% and 23.8% eyes in their normal group and the glaucoma group, respectively. A similar study on SD-OCT showed that the ISNT rule was applicable in 42% of normal subjects 23.…”

“…The usefulness of the NRR rules has been tested before 10–14. However, there are very few studies that look into whether the classical ISNT rule is applicable to the RNFL 15. Since the nasal rim is the last to be affected in glaucoma,16 we also tested the IST rule (inferior>superior>temporal) on the RNFL.…”

Presence of Peripheral Neuropathy Is Associated With Progressive Thinning of Retinal Nerve Fiber Layer in Type 1 Diabetes

“…In normal eyes, histologic as well as intravital OCT studies have reported that RNFL is thickest in the inferior quadrant followed by the superior quadrant. 22,23 We showed that the progressive reduction in RNFL was only statistically significant in the superior quadrant, whereby there was a linear annual thinning rate of approximately 2 lm/y in DPNþve individuals. The RNFL in the inferior (the thickest) and temporal quadrants showed no statistically significant alterations over 4 years in relation to neuropathy status.…”

The ISNT Rule: How Often Does It Apply to Disc Photographs and Retinal Nerve Fiber Layer Measurements in the Normal Population?

“…Therefore, many investigators have sought to determine whether the ISNT rule, either applied to the neuroretinal rim disc photos 12–15 or to RNFL thickness measurements, 16, 17 is useful in the diagnosis of glaucoma or not. However, the optic disc photo ISNT rule studies are conflicting, with some finding the ISNT rule and its variants clinically useful, 13, 14 while others have not.…”