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To the Editor :
—Ophthalmologists are accustomed to designate their findings on visual acuity by referring to a standard distance (for instance, 20/50, 20/80). On the other hand, it seems that in all tests given by the military services, a standard size letter is used and the examinee has to approach this letter until he is able to read it. Therefore, the official designations of visual acuity for the military services read 12/20, 15/20, etc.Examiners may have difficulty in comparing these two different kinds of designations. There is a simple way of conversion, by dividing the figure one wants to convert into 400. For instance : 20/25 of the ophthalmologists' designation equals 16/20 (400 divided by 25 equals 16), and 12/20 of the military services' designation equals 20/33 (400 divided by 12 equals 33).
Linksz A. DESIGNATION OF VISUAL ACUITY. Arch Ophthalmol. 1943;29(4):662. doi:10.1001/archopht.1943.00880160154012
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