In Reply.—
The optics of the eye are complex, and the factors that result in clear vision are multiple. Dr Chepko rightly notes another cause of suboptimal vision in dim lighting— spherical aberration.
For patients with no structural ocular disease, the impairment of distance vision in dim lighting is often referred to as "night myopia." Since my initial consideration of the question, I have encountered a thorough review of the subject by Hope and Rubin.1 These authors note that in addition to the factors of spherical aberration and chromatic aberration discussed above, changes in accommodation of the lens of the eye influence the vision in dim lighting. They suggest that all these factors can be contributory to blurring in darkness, in differing degrees in different individuals.
If spherical aberration were the major cause of distance blurring in dim lighting due to the larger pupil, it would seem that virtually everyone
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