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C.-Y. Cheng, T.-Y. Ho, P.-J. Lee, Y.-C. Ko, C. J. L. Liu; Assessment of the ISNT Rule by Peripapillary Retinal Nerve Fiber Thickness in Primary Open Angle and Angle-Closure Glaucoma. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2728.
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To determine whether peripapillary retinal nerve fiber layer (RNFL) thickness, as measured using scanning laser polarimetry (SLP), violates the ISNT rule in primary open angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).
Sixty-one patients with POAG, 61 patients with PACG, and 47 normal control patients were examined using SLP (GDx VCC). The peripapillary RNFL was divided into four sectors (superior, 32-122°; nasal, 122-238°; inferior, 238-328°; and temporal, 328-32°). The RNFL thickness in each sector was calculated and ranked to assess the ISNT rule. We also performed subgroups analysis based on disc size, which was measured and derived using the vertical and horizontal disc diameters shown on the GDx VCC printout after correcting for axial length.
The visual field mean deviation was comparable between the POAG and the PACG group (-11.45 ± 8.90 dB vs. -11.46 ± 7.98 dB, P = 0.991). The ISNT rule was fulfilled in 53% of normal eyes and 32% of glaucoma eyes in this study. The proportion of subjects violating ISNT rule was similar in the POAG (68.8%) and the PACG group (67.2%) (P = 0.846). The subgroup analysis showed that PACG subjects with smaller disc size were more likely to violate the ISNT rule, compared to those with larger disc size (82.8% vs. 53.1%, P = 0.014). This disparity was not observed in the POAG group.
The pattern of peripapillary RNFL loss with respect to the ISNT rule is similar between POAG and PACG eyes. In PACG eyes, the applicability of the ISNT rule based on peripapillary RNFL thickness in the differentiation of glaucomatous disc damage is affected by disc size.
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