In 1921, a study was reported by Ammann,1 in which the visual acuity of office patients was measured under ordinary conditions and with dark glasses, which, as the author stated, were of sufficient density to decrease the visual acuity for several lines on a reading chart. He found that the ratio between normal visual acuity and visual acuity with filter was as 1:0.3 to 1:0.5 in a group of normal patients. A group of amblyopic patients was examined in a similar manner, and the astonishing observation was made by Ammann that these eyes were not infrequently able to read the same line on the chart with and without filter.
Our recent electro-ophthalmographic observations2 about the extraordinary capacities of eyes with squint amblyopia under reduced illumination stimulated us to do a similar study, not only because Ammann's work has to our knowledge never been repeated or confirmed but also
von NOORDEN GK, BURIAN HM. Visual Acuity in Normal and Amblyopic Patients Under Reduced IlluminationI. Behavior of Visual Acuity With and Without Neutral Density Filter. AMA Arch Ophthalmol. 1959;61(4):533-535. doi:10.1001/archopht.1959.00940090535005