DURING the act of blinking the pupils are masked by the upper lids for an appreciable fraction of a second (c. 0·1–0·3 sec.) and, in consequence, vision is intermittent. The blackout index expresses the percentage of vision during which one is unsighted, and is obtained from the ratio of the blackout and interblink periods, the normal average value of the latter being for men and women c. 3·3 sec. In conversation, the average interblink period is only c. 2.7 sec.1.
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Hall, Sir Arthur, Brit. J. Ophthal., 29, 446 (1945).
Lawson, R. W., Nature, 161, 154 (1948).
Lord, Mary P., and Wright, W. D., Nature, 162, 25 (1948).
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LAWSON, R. Photographic Evaluation of Blackout Indices. Nature 162, 531–532 (1948). https://doi.org/10.1038/162531a0
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