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O. J. Knight, J. D. Oakley, M. Durbin, T. Callan, D. L. Budenz, Cirrus Normative Database Study Group; Effect of Ethnicity, Age, and Axial Length on Optic Nerve Head Parameters Measured by CirrusTM HD-OCT. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2750.
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To determine the effect of ethnicity, age, and axial length of optic nerve head (ONH) parameters as measured by Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA), in normal individuals.
Two hundred and eighty-four normal subjects were imaged at seven sites using Cirrus HD-OCT, with an optic disc cube scan that included 200x200 axial scans. The boundaries of the optic disc and the neuroretinal rim were determined using Cirrus 5.0 pre-production software. Disc area (DA), rim area (RA), average cup to disc ratio (CDR) over 180 meridians, vertical cup to disc ratio (VCDR), and cup volume (CV) were calculated. Axial length measurements were obtained using the IOL Master (Carl Zeiss Meditec, Dublin, CA). Linear regression was used to determine the extent to which ethnicity, age, and axial length affect the ONH parameters. Kruskal-Wallis test was used to compare medians for subjects who self-identified as being from European (Eur), African (Afr), Asian (Asn), or Hispanic (His) descent, with and without correcting for DA. There were (N) 122, 53, 73, and 36 subjects respectively.
There was a statistically significant difference among ethnic groups for all ONH parameters except RA. The ranges for ONH parameters categorized by ethnicity were: DA(mm2) 1.75 ± 0.31 for Eur to 1.98 ± 0.32 for Afr; RA(mm2) 1.30±0.23 for Eur to 1.38±0.24 for His; CDR 0.45±0.18 for Eur to 0.54±0.14 for Afr; VCDR 0.43±0.16 for His to 0.51±0.12 for Afr; CV(mm3) 0.12±0.12 for Eur to 0.21±0.16 for Afr. The Kruskal-Wallis test for differences due to ethnicity p-values for DA, RA, CDR, VCDR and CV are 0.002, 0.275, 0.005, 0.021 and 0.004 respectively. RA, CDR, VCDR, and CV were strongly dependent upon DA (R2 = 0.110, 0.344, 0.346, and 0.382, respectively). After a linear correction for DA, there was no statistically significant difference among ethnic groups for any ONH parameter. RA, CDR and VCDR depended upon age (R2 values = 0.040, 0.036, and 0.039 respectively). RA, CDR, and VCDR also depended upon axial length (R2 = 0.042, 0.020, and 0.028 respectively). There was no statistically significant dependence upon age or axial length for DA or CV.
There are ethnic differences in optic disc area, CDR, VCDR, and CV as measured by Cirrus HD-OCT. These differences may be explainable by the finding that optic disc area is strongly influenced by ethnicity. Rim area was the only ONH parameter that was independent of ethnicity.
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