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A. Ehsaei, C. M. Chisholm, E. A. H. Mallen, I. E. Pacey; Peripheral Visual Function in Myopia and Emmetropia. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3933.
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Increased axial length associated with myopia may affect visual performance through changes in retinal architecture, although there is conflicting evidence regarding the relationship between myopia and visual performance. Asymmetry also appears to be a common feature of the myopic retina. The purpose of this study was to assess peripheral visual performance in both horizontal and vertical meridians.
Ten highly myopic (HM; -5.00 to -9.00 D), ten moderately myopic (MM; -2.00 to -5.00 D) and twenty emmetropic (EM; +0.75 to -0.25 D) subjects, with astigmatism less than -0.50 D, were recruited. All were visually normal with visual acuity of 0.0 logMAR or better. The mean age of the subjects was 22.2 ± 3.7 years. Landolt C gap discrimination thresholds were determined at high (HC; 100%) and low (LC; 14%) contrast, using a 4AFC adaptive (2 up, 1 down) staircase paradigm, presented on a high resolution CRT monitor. Ocular dimensions between cornea and retina were established using partial coherence interferometry at ±30° eccentricity. All measurements were carried out in both horizontal (±30°, ±20°, ±10°, 0°) and vertical (±25°, ±20°, ±10°) meridians. The data were analysed using repeated measures ANOVA. The study was approved by the Research and Ethics Committees of the University of Bradford.
LC thresholds showed significant naso-temporal asymmetry in the horizontal meridian for all three groups (temporal>nasal) at 30° eccentricity (EM: p=0.000 MM: p=0.002, HM: p=0.007). HC thresholds in both horizontal and vertical meridians showed a trend towards higher values for the HM group compared to MM and EM groups, but this did not reach statistical significance. There was no significant asymmetry in HC threshold for any group in either meridian. At 30° horizontal eccentricity, corneal to retinal length was greater nasally compared to temporally in all 3 groups. LC thresholds were significantly higher in the HM group compared to the EM group in both horizontal (p=0.026) and vertical (p=0.045) meridians.
LC thresholds reveal better visual performance nasally than temporally, in agreement with studies of photoreceptor density. The HM group exhibit reduced visual performance in both meridians compared to MM and EM, consistent with our ocular dimension measurements.
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