Using reaction time in visual search and decision making task to measure visual field thresholds in multifixation perimetry

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PurposeThe ability to make eye movements to point the fovea toward object perceived in peripheral visual field is a fundamental feature of human visual system. We studied if reaction time (RT) in visual search task can be used for deciding if a peripheral visual field stimulus is visible when measuring visual field thresholds.MethodsOcusweep™ ambient light perimeter was programmed to display peripheral 0.2° stimulus of 100 ms duration for triggering a reflex saccade to point the fovea towards the location of the stimulus which was replaced with a faint arrow figure for reporting its direction with a button press and thus confirming foveal fixation. Next peripheral stimulus followed by a new arrow was then displayed. RT between button presses were recorded. Thresholds of the right eye of eight experienced healthy persons (mean age 43, range 22–58 years) using Humphrey 30–2 grid were measured with a staircase algorithm adjusting the intensity of the stimulus in response to the RT. Measurement reliability was estimated with catch trials, viewing distance controlled using ultrasonic rangers and variation in ambient room lighting (94–240 cd/m²) compensated using ambient light sensors of Ocusweep™.ResultsThresholds measured with RT perimetry were close to normal age corrected values of Octopus perimeter: mean MD was 0.7 dB and mean sLV 2.5 dB. The RT difference between positive (no stimulus, pure visual search, mean RT 1980 ms) and negative catch trials (suprathreshold stimulus, reflex saccade, mean RT 649 ms) was 1331 ms (SD 369 ms).ConclusionsReaction time perimetry can be used to measure visual field thresholds and also to assess reflex saccades.