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M. Hawker, G. Ainsworth, S.A. Vernon; The Normal Range of Asymmetry in Optic Nerve Head Morphometry in the Normal Elderly Population: The Bridlington Eye Assessment Project . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4801.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To define the normal range of asymmetry in optic nerve head parameters using Heidelberg retinal tomography (II) in the normal elderly population. Methods: Optic nerve head analysis of 918 eyes of 459 normal elderly patients was performed using the Heidelberg retinal tomograph (HRTII). All patients were consecutive in a cohort screened for eye disease. Normals were defined with a normal visual field on automated suprathreshold screening, intraocular pressure less than 22mmHg, and minimum corrected visual acuity of 6/12. All optic discs were contoured by two investigators and the mean parameters analysed. Differences in parameters between right and left eyes, and between superior and inferior neuroretinal rims were examined. Statistical analyses were performed using the Mann–Whitney U test (2–tailed). Results: Subjects’ mean age (262 female and 197 male) was 72.6 years (range 65.5–89.3). There was no significant difference in global disc area, or cup– or rim–related measures between right and left eyes. Clinically small but statistically significant asymmetry in height variation contour and cup shape measure were present. Median (2.5th/97.5th percentiles) global and temporal–inferior rim area to disc area asymmetry ratio (RADAAR; right minus left) were –0.012 (–0.211/0.168) and 0.002 (–0.306/0.288) respectively. In contrast to the standard HRT parameters, there was no significant difference in RADAAR for global or sectoral measurements based on disc area when disc area quartile groups were examined. Median (2.5th/97.5th percentiles) difference between superior minus inferior rim area to disc area was 0.000 (–0.209/0.235). Conclusions: This is the first large study of HRT II parameter asymmetry in the normal elderly population. Knowledge of the normal range of parameter asymmetry in an age group relevant to glaucoma may be useful in the discrimination of normal from early glaucoma. Asymmetry analysis may improve discriminatory ability by reducing parameter differences based on disc size. A new measure comparing superior and inferior rim/disc area ratio provides a morphometric equivalent of the glaucoma hemifield test and may also help discriminate normal and glaucomatous discs.
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