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P. Johnston, M. J. Byrnes, S. Saigal, D. R. Figueiredo Sena, G. Torkildsen, A. Ingerman; Visual Acuity, Near Visual Acuity, and Reading Acuity in Young and Old Subjects Under Photopic and Mesopic Illumination. Invest. Ophthalmol. Vis. Sci. 2010;51(13):971.
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Significant, age-related loss of visual function has been reported in healthy subjects. To understand the specificity of visual function loss in dry AMD, it is necessary to assess age-related vision loss in unaffected subjects. We compared best-corrected visual acuity (VA), near visual acuity (NVA), and reading acuity (RA) using photopic and mesopic illumination in young and old subjects.
Visual function at normal and low luminance was assessed in 10 eyes of 10 healthy subjects (5 aged 20-29, 5 aged 60+; BCVA 20/20 or better) using 3 charts (ETDRS (VA), SKILL (NVA), and MNRead (RA)). Subjects read the chart through neutral density filters for VA and RA to achieve mesopic illumination, and we compared performance using the light (white on black) and dark (black on grey) SKILL charts for NVA. Each test was repeated 3 times within 2 weeks. Reliability was assessed by fitting components of variance models and calculating the intraclass correlation coefficients (ICC). The effects of age and luminance on VA, NVA, and RA were then analyzed via two-factor ANOVA models with random effects. Models with and without age-luminance interactions were compared to determine which most accurately described the results.
ICC estimates ranges of 0.55-0.89 over all tests and luminance levels indicate moderate to substantial reliability. VA and NVA were more reliable than RA, and reliability was consistently better greater under photopic than mesopic luminance. The effect of luminance on VA was greater for older than for younger subjects (p=0.019), with mean logMAR differences of 0.36 and 0.26, respectively. Age-luminance interactions were not found for NVA (p=0.438) or RA (p=0.452). The mean vision loss in low luminance of all subjects was 0.76 (p<0.001) for NVA, and 0.21 (p<0.001) for RA.
Significant vision loss under mesopic illumination (relative to photopic) was observed for VA, NVA, and RA in both young and old subjects. No age related differences in loss of NVA and RA under mesopic illumination were observed. The loss of VA under mesopic illumination was approximately 1 line greater in older subjects than in younger subjects.
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