This research was prompted by the lack of quantitative and statistically significant evidence of deterioration of visual acuity in the course of prolonged visual work, despite subjective reports of tiredness. Earlier experimental efforts to produce such evidence were fruitless.*
In a previous study5 it was shown that the course of visual fatigue can be determined accurately in terms of quantitative measures of performance if the test stimulus itself, i. e., Landolt's broken circle, is used as measure, as well as the fatiguing stimulus. Such a testing situation is comparable to the situation in experiments on muscular fatigue, in which the weight lifted is both the measure and the cause of fatigue.
The present experiments have been performed in order to ascertain whether the decline in visual acuity continues in the course of repeated series of determinations (cumulative fatigue) and how it is affected by illumination level and reading.
BERGER C. Visual Acuity Decrease at Various Illuminations and Role of Reading. AMA Arch Ophthalmol. 1956;55(3):408-412. doi:10.1001/archopht.1956.00930030412011