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S. Patel, H. Leung, S. H. Schwartz, W. H. Swanson; Measuring Differential Visual Latency With a Simultaneity Paradigm. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2539. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To obtain reference norms that can be used to study function in the diseased eye, we (1) determined the symmetry of superior and inferior visual latency for brief flashes presented in the nasal visual field of healthy eyes and (2) ascertained the within and between session stability of these measurements.
A pair of vertically aligned squares (0.43 º each; 66 cd/m2 on a 6 cd/m2 background)), centered on the horizontal meridian and separated by 10 or 15 º, was flashed for 100 msec at various temporal asynchronies. The subject’s task was to indicate whether the top or bottom square appeared first, or whether they appeared simultaneously (or not sure). Interleaved staircases were employed to determine the boundaries of the simultaneity range. The initial asynchrony was 250 msec. Ten reversals were obtained for each staircase, and the final 8 were averaged to arrive at a boundary. To assess validity, data were fit with a Weibull function. The midpoint of the simultaneity range was taken as the latency difference between superior and inferior field (differential latency or DL). A DL of zero would indicate perfect symmetry.Twenty-two subjects participated in the study (range: 21 -79 yrs of age; mean 40 yrs). In a session, DL was determined both 5 and 15 º nasally using inter-trial step sizes of 20 and 40 msec (for a total of 4 conditions). During each session, 2 measures of DL were obtained for each of the 4 conditions. Two sessions, separated by at least a week, were conducted for each subject.
The average DL across all sessions/conditions (typically 16 measurements per subject) ranged from -15 (superior field faster) to +5 msec, with a mean value of -4 +/-6. The average width of the simultaneity range was 136 +/- 59 msec, and ranged from 35 to 270 msec. Neither retinal location (p = 0.912) nor the inter-trial step size (p = 0.442) significantly affected DL (within-subjects ANOVA). Within session DL variability ranged from 1 to 15 msec per subject with a mean of 9 +/-4, while between session DL variability ranged from 1 to 22 msec with a mean of 7 +/-4. Neither within nor between session DL variability were affected by retinal location (p = 0.767 and 0.331, respectively) or inter-trial step size (p = 0.440 and 0.267).
DL is similar across subjects, revealing little vertical asymmetry and minimal variability for the retinal loci and inter-trial step sizes that were tested. Both within and between session reliability were strong. These data suggest DL as a potential methodology to directly compare latencies of superior and inferior retinal loci in the diseased eye.
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