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D. Seidel, M. Day, N.C. Strang, L.S. Gray; The Effect of Target Luminance Upon the Microfluctuations of Accommodation in Emmetropia and Myopia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5588.
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Purpose: Accommodative microfluctuations have been found to have a larger magnitude in myopic subjects which has been attributed to reduced blur sensitivity and increased depth of focus. Increases in accommodation microfluctuations with reduced target luminance, thought to result from increases in depth of focus have also been reported in emmetropic subjects. In this study we examine whether the increased baseline microfluctuations found in myopes can be modified by changes in target luminance in a similar manner to emmetropic subjects. Methods: 14 (7 myopic and 7 emmetropic) healthy young adult volunteers with less than 0.50D of astigmatism participated with informed consent in the study. Subjects viewed a Maltese cross target through a +5D Badal lens at a vergence equal to their dark focus level of accommodation. The luminance of the target was varied from 0.004 cdm–2 to 15 cdm–2 in five approximately equal logarithmic steps. Accommodation was measured continuously over a period of two minutes using a Shin–Nippon SRW–5000 infrared autorefractor at a sampling rate of 52Hz. All myopic subjects were fully corrected with daily disposable soft contact lenses. Results: The myopic group had significantly larger (p<0.05) microfluctuations than the emmetropic group at all luminance levels. Increases in the magnitude of the microfluctuations occurred in both subject groups with reducing luminance, however, these increases tended to occur at lower luminance levels for the myopic subjects. Frequency analysis showed that these increases in the magnitude of the microfluctuations were caused by increases in the low frequency components (0.05–0.6Hz) of the microfluctuations. Conclusions: The differences in accommodation microfluctuations between myopes and emmetropes are consistent with the hypothesis of reduced blur sensitivity in the myopic eye. This suggests that the accommodation control system in the myopic eye operates with a larger dead–space than that found in emmetropic subjects.
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