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Heather A. Anderson, Karla K. Stuebing; A Conversion Equation to Predict Objective Accommodative Amplitude from the Subjective Push-Up Test. Invest. Ophthalmol. Vis. Sci. 2011;52(14):841.
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The standard clinical technique for measurement of accommodative amplitude is the subjective push up test. Although simple to perform, this test is not a true measure of accommodation and largely overestimates amplitude. The purpose of this study is to develop a conversion equation to predict objective amplitude from subjective push up measurements.
Monocular accommodative amplitudes were measured on the right eye of 227 subjects aged 3 to 64 years using both an objective technique and the subjective push-up test. For objective measurements, subjects were instructed to focus on a 20/40 letter on the near rod of the Grand Seiko autorefractor at 7 positions increasing from 2.5 to 8D, and then 6 additional positions from 10.5 to 30D as the letter was placed on a near rod attached to the forehead rest of the autorefractor. Repeated measurements of refraction were taken for each demand and the stimulus-response function plotted. Maximum amplitude was defined as the point at which the function peaked or plateaued. For subjective measurements, the same target was moved along an accommodative rule at increasing proximity until the subject reported first blur. Three repeated measurements were averaged to determine the maximum amplitude.
Multiple regression analysis was used to evaluate the correlation between objective amplitude, subjective amplitude, and age. Both subjective amplitude and age were significant predictors of objective amplitude (p < 0.001) and, when combined, accounted for a large portion of the variance in objective measurements across subjects (p < 0.001, R2 = 0.805). From this analysis, predicted objective amplitude was defined as 8.75 - (0.15*age) + (0.08*subjective amplitude). When comparing predicted objective amplitude versus measured objective amplitude for each subject, the formula accurately predicted the measured objective amplitude within ±2D for 90% of all subjects.
This data proposes a conversion equation which may be utilized clinically to convert subjective push-up amplitude measurements to objective amplitudes based upon patient age and push-up response. Future studies are needed on additional subject populations to further test the accuracy of the equation before it can be recommended for widespread use.
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