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B.L. Wood, T. Realini, J. Charlton, C. Moore; Evaluating Disc Size in Glaucoma Suspects With the Heidelberg Retina Tomograph (HRT) . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2522.
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Purpose: Asymmetry of optic nerve head size can manifest as asymmetry of the cup–disc ratio (CDR), as larger optic nerves often have larger cups. Clinical recognition of CDR asymmetry is straightforward, but size disparity between fellow optic nerve heads is easily overlooked, leading some patients with optic nerve head asymmetry to be diagnosed as glaucoma suspects based on CDR asymmetry. HRT provides a measure of optic nerve head size (disc area, measured in square mm). In this study, we report the use of the HRT to detect optic nerve head size asymmetry in glaucoma suspects with CDR asymmetry. Methods: A chart review was undertaken of all new patients referred in the past year for evaluation of glaucoma suspect status based upon optic nerve appearance (either asymmetric or symmetric but large cups). Only normotensive patients with normal standard automated perimetry were included. The main outcome measure was difference in mean disc area (as determined by the HRT software) between fellow eyes in two groups of patients: those with large but symmetric cupping (>0.5) and those with asymmetric cupping (disparity >0.1). Results: Mean disc area was statistically larger in suspects with large but symmetric cups (n=34) compared to suspects with asymmetric cupping (n=13) (2.63 vs. 2.35 square mm, p=0.017). Suspects with CDR asymmetry had statistically greater inter–eye differences in disc area than suspects with large but symmetric CDR (0.38 vs 0.23 square mm, p=0.038). Conclusions: Some glaucoma suspects with CDR asymmetry also have optic nerve head size asymmetry, which can be detected with HRT. In these patients, the apparent CDR asymmetry may be an anatomic artifact of nerve size disparity, and may be associated with a lower risk of glaucoma compared to patients with CDR asymmetry and symmetrically–sized optic nerves.
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