ISNT rule applicability based on optical coherence tomography parameters in a normal Portuguese population

Abstract

PurposeWe aim to determine the applicability of the inferior, superior, nasal and temporal neuroretinal rim (NRR) area characteristic configuration (ISNT rule) in adult normal Portuguese population based on spectral‐domain optical coherence tomographic (SD‐OCT) and assess demographic variations by age, sex, race and relation to optic disc area.MethodsProspective study with 188 eyes of 94 patients that underwent SD‐OCT with the new glaucoma module premium edition software (v.6.0). Patients with confirmed or suspected glaucoma, visual field defects, other optic disk or retinal abnormalities were excluded. Optic Nerve Head parameters such as Minimum Rim Width (MRW), Bruch's membrane opening (BMO) and thickness of peripapilar nerve fibre layer (RFNL) on four quadrants were analysed.ResultsThe mean age group was 55 years, 44% were men, 83% Caucasian and 17% melanodermic. Mean spherical equivalent was 0.10 (min −6.5, max +5), and mean best‐corrected visual acuity was 20/20 (min 20/40, max 20/16). NRR thickness area (MRW) was 376.0 μm ± 75.9, 345.4 μm ± 81.8, 365.1 μm ± 86.8, 240.5 μm ± 57.4, respectively on inferior, superior, nasal and temporal quadrants and ISNT rule was present in 23%. When excluding nasal quadrant (inferior > superior > temporal (IST) or inferior > superior (IS)) such configuration was present in 71% and 73% of patients, respectively. Mean age and mean optic disk/scleral area was higher in those with ISNT rule present (58.8 vs 53.7 years and 2.08 mm² ± 0.4 vs 1.98 mm² ± 0.5, respectively) but was not significant (p > 0.05) as were not sex and race differences.ConclusionsISNT rule in normal population is not confirmed by SD‐OCT assessed with ONH parameters and it is only present in 23% of eyes. The authors propose that a “IS/IST rule” seems more representative in a normal population as exclusion of nasal quadrant consideration increases prevalence.