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

Abstract

PurposeSimple 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.Methods158 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).ResultsThe 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).ConclusionsThis 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 pathway dominance (faster reaction times and better accuracy) was noted in patients with either type of retinal disease. 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 …”

“…The number and type of target (dark/light) were randomised across 200 trials. 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.…”

“…For the cohort of cone‐dominated diseases, in comparison with the normative database, 25%–30% ( n = 20) of the performance index measures and 40%–60% of the accuracy measures were greater than Q1 [25th percentile] of the normative database. 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.…”

“…Typically, sensitivity refers to the detection of a disease when it is present and specificity refers to the correct identification of negative cases when the disease is absent. 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.…”

“…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.…”