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H. C. Price, R. McLaughlin, P. M. Allen, D. O'Leary; Linearity of the Accommodative Response. Invest. Ophthalmol. Vis. Sci. 2007;48(13):960.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of increased sampling on the characteristics of the static accommodation response function. Previous studies suggesting a sigmoid-type response function were limited to a small range of stimuli at the distant part of the function.
11 subjects mean age 25.5 years ± 4 years participated in the study. Accommodative response functions (ASRF) were generated by stimulating accommodation in the right eye, (A) by altering vergence of light through a Badal system, and (B) with two free space targets of lines of letters of either, (i) constant height (5mm) at all distances, or (ii) constant angular subtense of 8.6 arc minutes (equivalent to Snellen 6/10). The response of the left eye was measured (Shin Nippon SRW5000 auto refractor), through a Wratten 88A filter for stimulus vergences of 0.0 - 4.5D in 0.50D steps for the Badal System and at 0.17D, then from 0.5 - 4.5D in 0.50D steps for the distance series.
Only one subject showed over-accommodation for distant targets in all 3 paradigms. Lag of accommodation with target B (ii) was slightly, but not significantly, smaller than lag for target B (i), averaging 0.37D. Target A gave lags of accommodation increasing monotonically over the full range of measurements. Linearity was high for all subjects with the 3 stimuli types over the range of 0.5D-4.5D, where all response values fell within 0.1D of the mean linear response, past the 0.50D stimulus. One-way ANOVA indicated a statistically significant difference between the test conditions (F2, 30=6.21; p< 0.01). Post hoc comparisons (Turkey HSD test) indicated that the mean slope for the Badal (M=0.88, SD=0.04) was significantly different from the slope for constant angle target (M=0.98,SD=0.87) and constant size target (M=1.00, SD=0.12). The two free space target presentations did not differ significantly from one another.
Instead of the typical sigmoidal shape to the ASRF, a linear response between 0.5D and 4.5D is noted. The gain of accommodative response is higher for free space targets than that of the Badal system. These results support the hypothesis that the accommodative lag is constant over a large range of distances, as expected from a depth of focus limited response, although a small deviation from this is seen when observing the response through a Badal system. The apparent sigmoidal response described classically may be the result of using an insufficient number of data-points.
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