This study investigated whether or not the response accommodative convergence to accommodation (AC/A) ratio in 30 visually normal subjects is linear with lens presentation order counterbalanced. Accommodative response was measured using the Shin Nippon SRW 500 infrared autorefractor. Accommodation was induced with full aperture trial lenses of strengths of -1.50, -3.00, -4.50 and -6.00DS. Heterophoria was measured with Maddox rod lens. Measurement was also taken at four metres using the modified Thorington technique. Subjects were aged 18-26 years (mean 20.3) and complete data was obtained for 23 subjects. Results showed a lack of linearity across accommodative demands with significant differences found between the -1.50, -4.50 and -6.00DS lenses. The general trend was an increasing responses AC/A with increasing accommodative stimulus. However, large variations occurred across the entire sample for different accommodative demands. No significant difference was found between myopic and non-myopic subjects. 

Non-linearity of the response accommodative convergence to accommodation ratio.
Johnston MS, Firth AY.
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Fiona Rowe (Prof)

Institute of Population Health, University of Liverpool, UK.

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