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P. Artal, C. Canovas, A. Mira-Agudelo; Night Myopia Revisited: Fact or Fiction?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6343.
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© ARVO (1962-2015); The Authors (2016-present)
Emmetropic eyes in daylight are thought to become myopic at low luminance viewing conditions. This phenomenon, commonly referred as night myopia, seems to be noticed first by Lord Rayleigh and extensively studied during the mid XX century. However, as it is pointed out in a classical study (Koomen et al., JOSA, 1951): "night myopia has been rediscovered from time to time and the literature is full of conflicting results". The purpose of this work is to revisit this phenomenon using an adaptive optics instrument operating in invisible infrared illumination to elucidate its actual magnitude and causes.
Visual acuity as a function defocus for a series of different experimental conditions was measured in 3 subjects. Tumbling-E letters were presented in a CRT-monitor for two luminance conditions: high (100 cd/m2) and low (with a 3.5-neutral density filter placed in the optical path). The low luminance measurements were performed after subjects dark adapted for around 30 minutes. Defocus and aberrations were continuously measured with the 1050-nm Hartmann-Shack sensor incorporated in the adaptive optics instrument. Measurements were performed for the following combinations of factors: i) different natural and artificial pupil diameters; ii) pseudo-monochromatic (green) and polychromatic (white) stimuli; iii) natural aberrations, all aberrations corrected, and the two previous conditions with spherical aberration set to 0 and 0.5 microns (for a 6-mm pupil).
Differences in the best focus position for high and low luminance were small or around zero for all the tested conditions. We were not able to find any significant myopic shift, except in one subject with induced 0.5 microns of spherical aberration where a shift around 0.5 D was found. Adding spherical aberration, one of the suggested possible causes of night myopia, did not modify best focus positions at different pupil diameters. We did not find any accommodation shift at low luminance as compared with the high luminance condition in any subject; two of them young adults with good accommodation response. The correction of high order aberrations nearly doubled visual acuity at the low luminance conditions, but at similar focus position.
Experiments using an adaptive optics instrument with invisible measuring light were performed to re-evaluate night myopia. We were not able to find significant myopic shifts at low luminance in the tested subjects. Neither spherical aberration nor accommodation shifts appears to have substantial effects in the phenomenon. Additional subjects should be tested to elucidate if night myopia actually exists.
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