Normal Value and Aging of AC/A Ratio Determined by a Gradient Method Using a Major Amblyoscope under Alternating Fixation.

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  • ＡＣ／Ａ比の正常値とその加齢変化について　交代固視下ｍａｊｏｒ　ａｍｂｌｙｏｓｃｏｐｅ法を用いて

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Accommodative convergence to accommodation ratio (AC/A ratio) is an important factor to make a diagnosis of nonrefractive accommodative esotropia (high AC/A type) and to investigate divergence excess exotropia. However statistically determined normal value of AC/A ratio is not so obviously described especially in the aged subjects. Deviation angle at near fixation in intermittent exotropia and that physiological exophoria are larger in the aged than in young subjects according to the recent Japanese literatures. We attempted to obtain the normal values of AC/A ratio in every age groups. The subjects were 114 normal volunteers; 18 subjects aged 5 to 9 years, 23 aged 10 to 19, 28 aged 20 to 29, 25 aged 30 to 39 and 20 aged 40 to 45. A gradient method using a major amblyoscope under alternating fixation was adopted. Accommodative stimuli were loaded by every one diopter using concave lenses of -1.00 to -5.00 diopters. In the subjects aged 30 or more, the accommodative stimuli were limited within the subjective amplitude of accommodation of each subject. Stimulus AC/A ratio was determined from an regression coefficient of objective angles of eye position to accommodative stimuli by a computerized least squares method. Means and standard deviation of AC/A ratio in the age groups were 4.3±1.0 (5 to 9 years), 4.3±1.1 (10 to 19 years), 3.9±1.1 (20 to 29 and 30 to 39 years), 3.4±0.9 (40 to 45 years) in prism diopters/diopters. AC/A ratio statistically reduced with aging (p<0.01, Jonckheere's test). The reduction of AC/A ratio by aging probably due to a conduction deficiency in the supranuclear or peripheral efferent system in the aged. We will be able to statistically evaluate the subject's AC/A ratio by comparing with the 95% confidence interval of normal value in each age group obtained in this study.

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