Visual Search Test (VST) ‐ reaction time perimetry with fixation objects detectable only by foveal vision

Abstract

AbstractPurpose To validate a novel perimetry method (Visual Search Test, VST) which is based on reaction times in visual decision‐making task, where the subject is allowed to move eyes and where the fixation is verified by the subject himself in contrast to standard automatic perimetry (SAP) where prolonged stationary fixation and external fixation monitoring apparatus is required.Methods Device (Ocusweep prototype, Ocuspecto Ltd, Turku, Finland) consisting of 35° arc (radius 54 cm) was constructed with six 3x5 LED arrays displaying 0.4°, 100 ms suprathreshold stimulus (Saccade Triggering Stimulus, STS) followed by an arrow (< or >) as a fixation object (FO) the recognition of which was reported by pressing a correct button. The intensity of FO was 3‐5 dB above the foveal threshold. With a correct button press a new peripheral STS & FO stimulus sequence was displayed in order to initiate a reflex saccade towards the STS. The time periods between button presses were recorded. 18 locations (up to 28° temporal, 20° nasal) along the meridians 0° and 8° of the visual field of left eye were tested. The center of the physiological blind spot of 11 healthy volunteers was measured with Octopus perimeter by custom program (1° oval grid of 139 test points). Reaction times within the blind spot area were compared to other locations.Results Reaction times within the blind spot area were slower compared to other locations in 10 of 11 subjects (AOV, p < 0.001 in 9 subjects, p < 0.006 in one subject).Conclusion Visual Search Test (VST) can be used to detect visual field defects. Commercial interest