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The effect of varying target size on negative relative accommodation (NRA) and positive relative accommodation (PRA)

1 May 1997


Clinical testing of negative relative accommodation (NRA) and positive relative accommodation (PRA) requires a nearpoint chart using small type. Most often, a 20/20 acuity demand is used and is considered to be the standard for these tests. Though it is understood that using different acuity demands affects the endpoints of these tests, differences have yet to be quantified for case analysis purposes. This study compares the endpoints of NRA and PRA with varying acuity demands and quantifies the differences. Fifty-six optometry students ranging in age from 22 to 38 years were tested using standard NRA and PRA test protocols on a specially constructed nearpoint card consisting of 20/20, 20/25, and 20/30 Snellen acuity lines of letters. Statistically significant differences were found in both blur-out and recovery values between each acuity demand on the NRA and PRA. Additionally, most mean values comparing monocular to binocular endpoints were statistically different. Results from this study demonstrate that different endpoints should be expected when using nonstandard targets or acuity demands for accommodative testing.


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