Elsevier

Ophthalmology

Volume 119, Issue 4, April 2012, Pages 723-730
Ophthalmology

Original article
The Accuracy of the Inferior>Superior>Nasal>Temporal Neuroretinal Rim Area Rule for Diagnosing Glaucomatous Optic Disc Damage

https://doi.org/10.1016/j.ophtha.2011.10.004Get rights and content

Purpose

To determine the accuracy with which the optic disc can be diagnosed as normal or glaucomatous according to the ISNT rule, whereby, in the normal eye, the neuroretinal rim area follows the order inferior (I) > superior (S) > nasal (N) > temporal (T).

Design

Prospective, cross-sectional, observational, case series.

Participants

Fifty-one normal individuals and 78 individuals with open-angle glaucoma exhibiting field loss (median mean deviation, −4.37 dB; interquartile range [IQR], −2.10 to −7.96 dB; median pattern standard deviation, 5.65 dB; IQR, 2.94 to 8.56 dB). The reference diagnosis was made by 2 experts on the basis of the appearance of the optic disc and of the corresponding visual field.

Methods

Stereoscopic optic disc photographs, acquired for each individual, were digitized at high resolution and analyzed using a digital, quad-buffered, stereoscopic viewing system in which a Z screen was used to dissociate the images to the 2 eyes of the observer. Three expert observers, trained to fellowship standard in glaucoma, independently undertook planimetry of the neuroretinal rim and of the disc margin from 1 eye of each individual, using a cursor moving in stereoscopic space to minimize parallax errors. Software automatically calculated the neuroretinal rim area in 10°, 30°, 40°, and 90° segments. For the ISNT rule to be obeyed, the 3 Boolean comparisons of the neuroretinal rim area, I>S, S>N, and N>T, had to be true. If any of the comparisons returned false, the rule was considered not to have been obeyed. Values were compared at a precision of 0.0001 mm2.

Main Outcome Measures

The outcome of the ISNT rule in terms of the 3 Boolean comparisons of the neuroretinal rim area was specified in terms of the sensitivity, specificity, and hence, the positive and negative likelihood ratios.

Results

Based on the ISNT rule being obeyed for 10° segments, the positive likelihood ratio among the 3 observers was 1.11 (95% confidence interval [CI], 0.99–1.25), 1.07 (95% CI, 0.94–1.21), and 1.06 (95% CI, 0.96–1.18), respectively. It was similar for the other segment sizes. Variants of the rule were not appreciably better.

Conclusions

The ISNT rule has limited utility in the diagnosis of open-angle glaucoma.

Financial Disclosure(s)

Proprietary or commercial disclosure may be found after the references.

Section snippets

Patients and Methods

The study used a cross-sectional, prospective, observational design.

Results

The 2 experts exhibited complete agreement for all 78 individuals with open-angle glaucoma. The assessment of 5 of the 51 normal individuals initially was discordant; these 5 individuals all had exhibited normal discs and intraocular pressures but manifested apparent field loss that had been designated as early glaucomatous. These 5 individuals each underwent re-examination of the visual field, which yielded a normal outcome in all 5 cases.

The descriptive statistics for the biometric variables

Discussion

The principle observation from this study is the low diagnostic power of the ISNT rule and its variants, for any given segment size, in the diagnosis of open-angle glaucoma exhibiting visual field loss ranging from mild to advanced. Although the comparison of the I>T combined with the S>T (i.e., I>T and S>T combined, indicating normality) rule provided greater diagnostic power, the magnitude of the improvement was of little clinical value.

The limitation of the ISNT rule stems largely from its

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    Manuscript no. 2011-233.

    Financial Disclosure(s): The author(s) have made the following disclosure(s):

    James E. Morgan - Royalties - Haag Streit, UK (paid into a Cardiff University research account).

    Supported by the Wales Office for Research and Development, National Assembly for Wales, Cardiff, United Kingdom (grant no.: SG99/265); and the National Eye Research Center (UK), Bristol Eye Hospital, Bristol, United Kingdom. The funding organizations had no role in the design or conduct of this research.

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