Detecting the Physiological Blind Spot with Reaction Time Perimeter

Objective: To study the ability of a novel reaction time perimeter to detect a physiological blind spot. Methods: The location of the physiological blind spot of 11 healthy volunteers was determined with two independent methods, first by Octopus custom-made blind spot visual field program, and second by Fundus photography with a method previously described by the authors. With reaction time perimeter saccade triggering stimuli (STS) were shown in predetermined locations of the visual field in order to initiate saccades. 

An STS was followed by an FO (fixation object) i.e., an arrow head pointing either to the right or left at the same location as the previously shown STS. The recognition of the FO was reported by pressing a correct button(right or left respectively) thus verifying accurate fixation by the fovea. Time intervals between button presses were recorded. Reaction times for detecting the STS within the blind spot area were compared to those for detecting the STS in other locations of the visual field. Results: Reaction times within the blind spot area were longer compared to those in other locations in 10 of 11 subjects (Analysis of variance), p<0.001 in 9 subjects, p<0.006 in one subject). Conclusion: A physiological blind spot can be detected with reaction time perimeter.

The ability to move the eyes towards an object perceived in the peripheral visual field in order to fixate with the fovea is a fundamental feature of the visual system. Visual processing speed, which is defined as the time needed to make a correct judgment about a visual stimulus, is commonly studied in behavioral research by measuring reaction times. Visual field defects can be quantified by standard automated perimetry (SAP), but it has limited power to predict the impact of disease on the ability to perform activities of daily living. The testing situation in SAP involves maintaining a steady fixation whilst keeping the head still on a head rest making it very unnatural compared to real-world viewing tasks.

In this pilot study, our purpose was to determine if reaction time perimeter allowing free head and eye movement and thus simulating the normal features of the visual system can be used to detect a physiological blind spot.

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