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M. G. Tong, J. Mohay; Differential Diagnostic Features of Glaucomatous and Non-Glaucomatous Optic Neuropathies by Heidelberg Retina Tomograph (HRT) Stereometric Measurements. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2741.
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Excavation of the optic nerve with thinning of the neuroretinal rim is considered a hallmark of glaucomatous optic neuropathy. However, a variety of central nervous system (CNS) disorders can also present with similar findings. The purpose of this study is to determine whether unique changes in the optic nerve can distinguish between these two disease processes.
During a retrospective chart review, 61 eyes with a linear cup/disc ratio of 0.6 - 0.7 were divided into three groups: group 1 (25 eyes) had field loss due to CNS abnormalities; group 2 (18 eyes) had normal tension glaucoma (NTG); group 3 (18 eyes) had high tension glaucoma (HTG). Variables measured by the Heidelberg Retinal Tomograph (HRT) II (Heidelberg Engineering, Heidelberg, Germany) included disc area, rim area, rim volume, average cup depth, maximum cup depth, and nerve fiber layer thickness. Additional variables included: mean deviation and pattern standard deviation from the most recent Humphrey Field Analyzer II (Carl Zeiss Meditec, Dublin CA) 24-2 test, lowest recorded IOP, maximum IOP, central corneal thickness, and clinical documentation of pallor. Statistical analysis was performed using the software R version 2.10.0.
Analysis of variance (ANOVA) revealed statistically significant differences with regard to HRT rim volume (p=0.02) and HRT nerve fiber layer thickness (p=0.03). Group 1 had a greater rim volume (mean= 0.325 cmm, SD=0.187) and nerve fiber layer (mean=0.214 mm, SD=0.083) when compared to group 2 (mean=0.194 cmm, SD=0.114 and mean=0.149 mm, SD=0.068 respectively) and group 3 (mean=0.246 cmm, SD=0.083 and mean=0.174 mm, SD=0.079 respectively). Fisher's exact test revealed that more patients in group 1 than in groups 2 or 3 had optic nerve pallor (p=0.001). ANOVA on all other variables did not reveal a significant difference.
The optic nerve characteristics of patients with an increased cup/disc ratio and coexisting CNS pathology include a larger rim volume and thicker nerve fiber layer but are otherwise similar to disc characteristics of patients with NTG and HTG.
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