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Sympathetic inhibition of accommodation following sustained nearwork in myopes and emmetropes.

Vasudevan B, Ciuffreda KJ, Gilmartin B

Vision Science, SUNY Optometry, 33 West 42nd street, New York CIty, New York, 10036, United States.

Purpose: The purpose of the present study was to assess the effect of a sympathetic inhibitory pharmacological agent, namely timolol maleate, on the magnitude of NITM and its decay in different refractive groups for an extended near task duration, as well as to determine the proportion of the young-adult population manifesting effective sympathetic access, under naturalistic closed-loop viewing conditions. Methods: 10 emmetropes (EMMs) and 10 myopes were tested. They read binocularly for 1 hour at a distance of 35-40 cms. NITM was calculated as the difference in distance refractive state post- versus pre-task immediately following reading. All subjects received timolol maleate to block the sympathetic nervous system, and betaxolol as a control agent, in independent test sessions separated by at least 3 days. Forty minutes after drug instillation, the NITM measurement procedure was repeated. Results: With regard to initial NITM magnitude, it was larger in the myopes than in the EMMs both pre- and post-timolol instillation. Furthermore, NITM magnitude in subjects with sympathetic access was increased following timolol instillation. In contrast, with the control agent betaxolol, there was no increase. With regard to NITM decay duration to baseline, it was increased following timolol instillation in the myopes only. Lastly, only 15% of the subjects (n=3 myopes) demonstrated effective and significant access to sympathetic facility. Conclusions: Myopes demonstrated an increase in decay duration with timolol. This suggests impaired sympathetic inhibition of accommodation. This may be a precursor for myopia progression in some individuals.

Published 4 July 2008 in Invest Ophthalmol Vis Sci.
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