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M. Bertolotto, F. Allavena, A. Perdicchi, S. M. Recupero, G. A. Calabria, M. Iester; The "ISN’T Rule" in Healthy Subject Optic Nerve Head by Confocal Scanning Laser Ophthalmoscopy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5815.
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The aim of this study was to verify by using Heidelberg Retina Tomograph 3 (HRT 3, Heidelberg Engineering, Heidelberg, Germany; software version 3.0) if the value of rim area (RA), rim volume (RV) and cup shape measure (CSM) of the optic nerve head confirmed the Jonas study1 ("ISN'T rule") where he demonstrated that in normal subjects the rim had a characteristic configuration with the rim width being broadest in the inferior disc region, followed by the superior sector, the nasal area, and finally the temporal sector.
This is a prospectively planned cross-sectional study. Two hundred and twenty five healthy eyes were recruited into this study. All the included subjects had normal ocular examination, an intraocular pressure less than 21 mmHg and normal visual field by Humphrey Field Analyzer (program 24-2, SITA STANDARD). For each patient, the optic nerve head was morphometrically evaluated by using the HRT3. All data were analyzed by ANOVA test and by Turkey’s Multiple Comparison Test.
The mean disc area was 2.112 +/- 0.476 mm2 (mean +/- standard deviation). Significant (P<0.001) differences were found between the temporal rim volume and the superior (difference= -0,081), the nasal (-0,087), and the inferior rim volume (-0,09), but no significant difference was found among superior, nasal and inferior rim volume. When the rim area was considered, a significant statistically change (P< 0.001 ) was found between temporal rim area and superior (- 0,141), nasal (- 0,163), and inferior rim area (- 0,162). No significant difference among superior, nasal and inferior rim area. The temporal cup shape measure was significantly different from the other disc sectors and no significant difference was found between the superior and the inferior CSM values.
In healthy subjects the rim area and volume distribution wasn’t congruent with the "ISN'T rule" found, when a confocal scanning laser ophthalmoscopy was used. The shape of the rim was similar in the superior and in the inferior sectors.
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