The “speed” of acuity in scotopic vs. photopic vision

Abstract

Purpose The effect of duration of optotype presentation on visual acuity measures has been extensively studied under photopic conditions. However, systematic data on duration dependence of acuity values under mesopic and scotopic conditions is scarce, despite being highly relevant for many visual tasks including night driving, and for clinical diagnostic applications. The present study aims to address this void. Methods We measured Landolt C acuity under photopic (90 cd/m 2), mesopic (0.7 cd/m 2), and scotopic (0.009 cd/m 2) conditions for several optotype presentation durations ranging from 0.1 to 10 s using the Freiburg Acuity and Contrast Test. Two age groups were tested (young, 18-29 years, and older, 61-74 years). Results As expected, under all luminance conditions, better acuity values were found for longer presentation durations. Photopic acuity in young participants decreased by about 0.25 log units from 0.1 to 10 s; mesopic vision mimicked the photopic visual behavior. Scotopic acuities depended more strongly on presentation duration (difference > 0.78 log units) than photopic values. There was no consistent pattern of correlation between luminance conditions across participants. We found a qualitative similarity between younger and older participants, despite higher variability among the latter and differences in absolute acuity: Photopic acuity difference (0.1 vs. 10 s) for the older participants was 0.19 log units, and scotopic difference was > 0.62 log units. Conclusion Scotopic acuity is more susceptible to changes in stimulus duration than photopic vision, with considerable interindividual variability. The latter may reflect differences in aging and sub-clinical pathophysiological processes and might have consequences for visual performance during nocturnal activities such as driving at night. Acuity testing with briefly presented scotopic stimuli might increase the usefulness of acuity assessment for tracking of the health state of the visual system.

Refractive and visual function changes in twilight conditions

“…In terms of logMAR visual acuity, there was a one-step decrease from bright to twilight, similar to the logMAR visual acuity measured at a visual target luminance of 3 cd/m 2 in a similar twilight study [13]. A decrease in logMAR visual acuity of two or three levels has been reported in mesopic vision with a visual target luminance of less than 1 cd/m 2 [12]. Therefore, when establishing a method for evaluating visual function in the twilight as an assumption for driving at sunset, luminance between 3 cd/m 2 and 10 cd/m 2 is considered to be similar to that of actual twilight.…”

“…Most studies on twilight vision show luminance of 1 cd/m 2 or less, and studies assuming slightly brighter twilight vision show luminance of 3-5 cd/m 2 or less. When sunset is assumed to be in twilight, these studies have a luminance that is closer to nighttime [12][13][14][15]. We measured the luminance of white lines, road signs, and road surfaces on roads finclusioor 30 min before and after sunset to conduct our research assuming everyday scenes.…”

Is Developmental Dyslexia Due to a Visual and Not a Phonological Impairment?

“…First column on the left: fixation times of pseudowords; second column: number of subjects who were able to read 3-letter pseudowords within fixation times between 250 and 500 ms; third column: number of subjects who were able to read 4-letter pseudowords within fixation times between 250 and 500 ms; fourth column: number of subjects who were able to read 5-letter pseudowords within fixation times between 250 and 500 ms. Fifth column: number of subjects who were able to read 6-letter pseudowords within fixation times between 250 and 500 ms. The improvement in the ability to recognize pseudowords simultaneously when the fixation time is prolonged is due to temporal summation [152][153][154][155][156][157][158][159][160][161][162][163][164][165]. Detection and recognition of visual stimuli [152][153][154][155][156][157][158][159], and visual acuity improve when fixation time increases [160][161][162][163][164][165].…”

“…The improvement in the ability to recognize pseudowords simultaneously when the fixation time is prolonged is due to temporal summation [152][153][154][155][156][157][158][159][160][161][162][163][164][165]. Detection and recognition of visual stimuli [152][153][154][155][156][157][158][159], and visual acuity improve when fixation time increases [160][161][162][163][164][165]. This improved visual performance results from an increase in visual processing capacity as the fixation time is extended.…”

“…Taken together, experimental results [57][58][59] have shown that the ability to recognize several letters in a word or pseudoword simultaneously depends on the fixation time. Temporal summation [152][153][154][155][156][157][158][159][160][161][162][163][164][165] can explain the ability to recognize more letters in pseudowords simultaneously when the fixation time is prolonged. Regardless of the fixation time, there is an individual limit to the number of letters a person can recognize simultaneously.…”