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F.A. Vera-Diaz, N.C. Strang, B. Winn, J. Gwiazda; Accommodative Tracking is Attenuated in Myopia . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3116.
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Purpose: Myopic subjects have reduced accommodative accuracy under steady-state viewing conditions. In addition, they have reduced dynamic responses to step-wise changes in stimulus vergence following a period of sustained viewing. In this study the closed-loop accommodation response to sinusoidally-modulated changes in stimulus vergence (accommodation tracking) is measured in an attempt to investigate the relationship between temporal frequency and accommodation inaccuracy in myopia. Methods: Monocular closed-loop accommodation responses were measured in a group of emmetropes (n=6) and myopes (n=6) using a dynamic tracking infrared optometer (SRI). A high contrast photopic (30cdm-2) stimulus was presented in a Badal optometer, viewed through a 5mm Maxwellian fixed pupil, and modulated sinusoidally (0.05-0.5Hz) over a 2D range (2D-4D). Power spectrum analysis was used to calculate gain and phase. Results: Emmetropic subjects demonstrated a typical reduction in gain and an increased phase lag at higher temporal frequencies. Myopic grouped mean data showed a significant decrease in accommodative gain compared to emmetropes (p<0.01) which was not temporal frequency dependent. Myopes also exhibited an increased phase lag compared to emmetropes at all temporal frequencies (p<0.01). Conclusions: Blur-driven accommodative tracking is attenuated across all temporal frequencies in myopia. A similar level of myopic accommodation inaccuracy was found at all temporal frequencies.
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