Age-related decline in function of ON and OFF visual pathways

Abstract

Purpose A simple psychophysical paradigm is available as a digital application in iOS devices such as iPad to measure the function of ON and OFF visual pathways. However, an age-matched normative database is not readily available. The purpose of the study is to evaluate the response of ON and OFF visual pathways as a function of age. Methods 158 normal healthy adults (84 males and 74 females) whose age ranged 18–80 years participated in the study. None of them had any ocular disease (except cataract of grade II or less) and visual acuity of ≤ 20/25. Monocular testing (only one eye) was performed on the ‘EyeSpeed’ application on an iPad at 40cm distance. The targets ranged between 1 to 3 light or dark squares presented randomly in a noise background and participants responded by indicating the number of squares by touching the screen as fast as possible. The main outcome variables are reaction time, accuracy and performance index (1 / speed * accuracy). Results The median reaction time was shorter (Median (IQR): 1.53s (0.49) [dark] Vs 1.76s (0.58) [light], p < 0.001) and accuracy was higher (97.21% (3.30) [dark] Vs 95.15% (5.10) [light], p < 0.001) for dark targets than the light targets. Performance index and reaction time for both target types significantly correlated with age (ρ = -0.41 to -0.43; p < 0.001). Conclusions This normative database will be useful to quantify disease-specific defects. More importantly, the ON pathway function can potentially serve as a surrogate for rod photoreceptor function.

Tablet‐based ‘ON/OFF’ pathway test can distinguish between rod‐ and cone‐dominated diseases

“…On average, individuals with no ocular pathology would take approximately 5-6 min to complete the test. 24 However, in this study, the overall completion time was expected to be longer owing to the longer reaction times resulting from the ocular pathology.…”

“…In the present study, healthy age-matched subjects were not tested as an age-matched normative database is already available. 24 Here, sensitivity and specificity parameters were used to distinguish between the two groups of diseases, rather than between the disease and a control group. The gold standard for the presence of true disease was taken from the combination of patient symptoms, ophthalmological findings and ancillary diagnostic testing such as ERG, OCT and fundus autofluorescence.…”

“…This finding is consistent with the pattern observed in healthy subjects. 18,19,21,24 However, the ON pathway dominance is dependent upon the luminance of the stimuli. 29 As expected in the hypothesis, the reaction times for the ON pathway function in rod-dominated diseases were much longer than those seen in cone-dominated disease.…”

“…Approximately 30% of the reaction time measures were lower than Q3 [75th percentile] of the normative database. 24 Note that the quartiles considered for reaction time are different from the outcome variables such as accuracy and performance index owing to the different directionalities of what constitutes a normal value. However, none of the reaction time/performance index measures in the rod-dominated cohort were within the respective quartile values of the normative database.…”

“…This study reports results obtained using an iOS-based application called 'EyeSpeed', whose stimuli have been validated to differentiate between the functions of the ON and OFF pathways. 18,22 Also, there is now a normative age-matched database available for this iPad-based testing, 24 which allows us to compare and quantify the deficits.…”