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E.N. Harb, F. Thorn, D. Troilo; Accommodation During Sustained Near Reading . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2732.
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Purpose: The association between myopia and reading suggests that accommodation may be related to the progression of myopia. Studies in animals and humans have suggested that a relationship, if one exists, may involve inaccuracy in accommodation during near vision. In this study we examined accommodation over an extended period of sustained near reading to determine whether accommodative changes occur that could contribute to a blur-driven change in refractive state. Methods: Accommodation was measured in 8 adults during 10 minutes of sustained reading at several distances (1.5 D, 2.5 D, and 3.5 D). One subject was subsequently diagnosed with accommodative excess and not included in the group analysis. Subject refractive error ranged from +1.0 to –7.0 D. All subjects were measured with pupil dilation (2.5% phenylephrine) and full contact lens correction. Refractive state before and after the reading period, and accommodative state during reading, was measured with an IR video refractor (MultiChannel Systems). The PowerRefractor was calibrated against refractions determined retinoscopically and subjectively on a separate set of subjects under cycloplegia (1% cyclopentolate). Results: The amount and stability of accommodation over a sustained period of reading differed among the subjects in this study. The standard deviations of the accommodative response over the entire reading period ranged from 0.14 to 0.83 D at the 1.5 D demand, 0.18 to 0.55 D at 2.5 D, and 0.32 to 1.2 D at 3.5 D. At the 1.5 and 2.5 D demands accommodation was relatively stable over the reading period for 4 of the subjects (average s.d. = 0.27 at 1.5 D and 0.39 at 2.5 D). The accommodative states of the other subjects were more variable (average s.d = 0.65 at 1.5 D and 0.52 at 2.5 D) with accommodation either increasing or decreasing over time. The variability in accommodation was generally highest for all subjects at the 3.5 D demand (average s.d. = 0.78) compared to the other demands (ANOVA p<0.05). In the subject with accommodative excess, the variability in accommodation was high (0.89 at 1.5 D, 0.91 at 2.5 D, and 0.87 at 3.5D) and an increased lead in accommodative state was exhibited over time. Conclusions: The increase in variability observed with increasing demand and the individual differences in the accommodative response suggest that accommodation may change over time during sustained near reading in some individuals and could contribute to a blur-driven eye growth response. More subjects are required to define further the relationship between refractive state and the accommodative response to sustained reading.
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