A limited study has shown that the diameter of the pupil of the eye is not related directly to the sensation of discomfort which results from a bright light source in the field of view. Other factors, especially the illumination received at the eye, govern the pupil diameter. The more concentrated the source producing the illumination at the eye, the greater the contraction of the pupil. When the eye is subjected to intolerable glare, the pupil not only contracts, but varies in diameter, dilating and contracting irregularly every few seconds.
The study indicates that the pupil diameter by itself cannot be used as an objective indicator of the degree of glare discomfort.
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