Vision is such a complicated phenomenon and is dependent on so many variables that no single test can be devised by which it can be accurately measured for all purposes. In practical life, however, no doubt the most important factor in visual acuity is the resolving power of the eye. This is commonly measured by determining the smallest visual angle perceptible, the minimum separable. Such determinations, however, do not reveal the full resolving power of the eye, for the best possible vision shown by them corresponds to a visual angle of only about 30 seconds, whereas by certain methods which measure the alining power it can be shown that the eye is capable of much finer discrimination than this. It should not be assumed from this fact, however, that tests based on the minimum separable are necessarily less precise than those based on the alining power. While, so far
VERHOEFF FH. A NEW TEST FOR VISUAL ACUITY. Arch Ophthalmol. 1933;10(2):226–230. doi:10.1001/archopht.1933.00830030074006
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