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Tawna L Roberts, Karla K Stuebing, Heather A Anderson; Comparison of Objective and Subjective Accommodative Response from Preschool to Pre-Presbyopia. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3763.
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© ARVO (1962-2015); The Authors (2016-present)
A typical accommodative response curve shows as the accommodative demand increases, the accommodative lag increases. This trend is apparent from childhood to pre-presbyopia, despite differences in accommodative amplitude with age. The purpose of this study was to investigate the magnitude of the accommodative response relative to the demand with respect to subjective reports of whether the stimulus was clear or blurry and whether that response differed with age.
Accommodative response was measured with the Grand Seiko autorefractor in 148 subjects age 5 to 35 years. Subjects viewed a 20/40 letter at 13 discrete distances of increasing proximity starting from 40cm and ending at 3.33cm (demand range: 2.5 - 30 D). Five measures of spherical equivalent refraction were averaged for each target position and expressed as the accommodative response. At each stimulus position the subject reported whether the stimulus was clear or blurry. An accommodative response ratio (ARR) was calculated (accommodative response /accommodative demand) at the first demand for which the subject reported blur (termed condition 5) and compared to the ARR calculated for the previous four lower demands reported as clear (conditions 1-4 with condition 1 being the least accommodative demand).
The mean ARR for conditions 1-5 was 0.75, 0.76, 0.75, 0.71, and 0.59, respectively. Conditions in which the stimulus was clear (1-4) were compared with both repeated measures ANOVA and MANOVA. ARR did not significantly differ across conditions for ANOVA (F=2.26, p=0.08), but did differ with MANOVA (F=2.87, p=0.04), although the largest difference was only 5%, which is unlikely to be clinically meaningful. There was no statistically significant age effect using either analysis (ANOVA, F=0.10, p=0.96; MANOVA, F=0.15, p=0.93). The mean ARR for conditions 1-4 combined was significantly different as compared to condition 5 by the single degree of freedom contrast test in which subjects reported the target to first become blurry (F=58.05, p<0.001).
These data suggest that on average, accommodative responses meeting 70% of the stimulus demand are sufficient for subjects to perceive a clear target. This finding did not vary as a function of age and is consistent with clinical norms defining a 0.75 D lag as the upper normal limit for habitual near working distances of 40cm (1.75D response = 70% of 2.5D demand).
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