The terms minimum visible, light threshold and minimum light visible are synonymous and signify the least intensity of light visible to the eye, in other words, the ability of the eye to adapt itself to darkness. Physiologically, dark adaptation, or the light threshold, is a function of the cruder retinal elements, namely, the rods and the visual purple, in contradistinction to light adaptation, a function of the more refined and sensitive cone elements.
The subject of dark adaptation was first brought to the attention of the medical world through the work of Aubert1 in 1862. Since then the problem has attained a more scientific level by standardization of the light intensity in the testing device, as well as of its calibration. Within recent years the subject of dark adaptation has become increasingly important, owing to the work of Wald,2 who observed that the visual purple in the eyes
FELDMAN JB. LIGHT THRESHOLD: ITS CLINICAL EVALUATION. Arch Ophthalmol. 1941;26(3):466–471. doi:10.1001/archopht.1941.00870150140008
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