Is the ISNT rule violated in early primary open-angle glaucoma—a scanning laser tomography study

Abstract

Aims To evaluate the relevance of the ISNT rule with reference to the optic nerve head, in differentiating normal and early glaucoma eyes and neuroretinal rim (NRR) area ratios as measures of glaucomatous optic neuropathy by confocal scanning laser ophthalmoscopy (Heidelberg retina tomography (HRT) II). Methods The study included 136 control eyes and 63 eyes of early primary open-angle glaucoma. Each patient underwent a complete ophthalmic examination, HRT II (software 2.01) and achromatic automated perimetry using the Humphrey field analyzer Full threshold program 30-2 or 24-2. Topographic HRT parameters (disc area and rim area) were compared between the groups. To assess the statistical significance of differences between the study groups, the Student's t-test was used. Results The ISNT rule was applicable in 71% of normal eyes and 68% of early glaucoma eyes. The superior to inferior area ratio was 0.9670.01 in the normal group and 0.9070.02 in the glaucoma group. There was a loss of approximately a quarter of the NRR in the inferotemporal and superotemporal quadrants. The inferonasal sector showed the least loss of NRR (4.34%). Conclusion The inferior NRR is marginally wider than the superior NRR in about 2/3 of normal eyes, but could not be clinically appreciated in many of these. The characteristic configuration of a normal optic disc with the rim width being greatest in the inferior disc region followed by the superior disc region was maintained even in most patients with early glaucoma.

Effect of Age and Disc Size on Rim Order Rules by Heidelberg Retina Tomograph

“…Furthermore, 73% of patients complied with the I > S > T (IST) rule in our study, which was similar to the findings of the HRT II study by Sihota et al 5 However, Sihota et al 5 compliance amongst normal and early glaucoma eyes (71% vs. 68%). Morgan and colleagues conducted a cross-sectional comparison of 51 normal eyes and 78 glaucomatous eyes with documented visual field loss using digitized stereoscopic optic disc images.…”

“…2 Recent studies assessing the ISNT rule fulfillment by Heidelberg Retina Tomograph (HRT) have had varying results (12% to 56% fulfillment). [3][4][5] This has led to interest in alternative rules such as IS (I > S) and IST (I > S > T) rules, which have fulfillment rates of 56% to 93% 2,3,5-8 and 71%, 5 respectively. In addition, given the variability of ISNT rule fulfillment, understanding factors associated with ISNT rule violation would be clinically relevant.…”

Diagnostic Performance of the ISNT Rule for Glaucoma Based on the Heidelberg Retinal Tomograph

“…Second, a segmental measure of neuroretinal rim area on the HRT is expected to provide more objective quantification of rim characteristics, than rim width measurements, which require precise determination of the cardinal meridia. 8 Furthermore, a patient-friendly device allowing automated quantification of the neuroretinal rim, such as the HRT, is preferential to manual planimetry for populationbased assessment, which is the cohort of interest in our study. Finally, we controlled for potential confounders, allowing confirmation that disc area independently influences the performance characteristics.…”

“…6 However, several other clinic-based studies also raise concern that the ISNT rule may not be sufficiently valid to diagnose glaucoma. [7][8][9] Despite the wide use of the ISNT rule in clinical practice, the application of the ISNT rule generally is conducted with ophthalmoscopy and, therefore, is a subjective clinical sign. The Heidelberg retinal tomograph (HRT), a confocal scanning laser ophthalmoscope, is able to provide objective and reproducible measurements of the optic nerve head [10][11][12][13][14][15] and, thus, may have potential use for population-based glaucoma screening.…”

Different Clinical Parameters to Diagnose Glaucoma Disease: A Review

“…This means VCD and VDD of Indians are usually different from EuropeanAmericans. In retinal rim area estimation, 71% of healthy eyes obey the rule ISNT but remaining 29% of normal eyes do not obey the ISNT rim area rule [23]. In central cornea thickness estimation, if CCT is less than 0.50mm, it indicates the sign of glaucoma.…”