Monday, May 22, 2006

35

Night Myopia



Light rays at the edge of the human lens are refracted more than those at the center of the lens. Because our pupils are larger at night, more spherical aberration is present under lower light conditions. A refractive shift towards more myopia is needed to compensate for this increase in spherical aberration. Additionally, accommodation does not go to a neutral state under low light conditions. The visual system actually accommodates approximately 0.75D under low light conditions. These changes result in a need for more minus or less plus correction for those individuals, such as over the road truck drivers, who need to function with their highest visual clarity at night.

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