Assessment of Visual Scanning Parameters in a Preferential Looking Procedure

Abstract

Purpose: : Preferential looking (PL) procedures use qualitative assessment of infants’ visual scanning behaviour to determine visual acuity (VA). Our purpose was to study quantitatively how visual scanning parameters change as a function of VA.

Methods: : Ten subjects were presented with a set of 14 visual stimuli (stimuli included 3 uniform grey fields and 1 field with gratings) spanning the range from 1.3 logMAR to -0.07 logMAR. A remote gaze-tracking system was used to monitor the subjects` eye movements. The time to fixate on the field with the gratings (latency) and the percentage of time on the field with the gratings (PTT) were calculated.A four-alternative forced-choice psychophysical test (4AFC) was performed with the same visual stimuli.

Results: : The mean latency for gratings with spatial resolutions that are at least 0.2 logMAR above the subjects’ VA was approximately constant at 817 msec. The mean latency increases to 1700 msec at the VA threshold and to 2265 msec for gratings below the VA threshold. The mean PTT for gratings with spatial resolutions that are at least 0.2 logMAR above the subjects’ VA was approximately constant at 72.5%. The mean PTT decreased linearly to 38% at the VA threshold and to 24% below the VA threshold.

Conclusions: : The study shows that for gratings with spatial resolutions that are at least 0.2 logMAR above the subjects’ VA, both the initial response to the presentation of the stimulus (i.e. latency) and the continuous examination of the stimulus (i.e. PTT) can be used to assess subjects’ ability to detect the gratings. As the spatial resolution of the gratings approach the subject’s VA the PTT is a better indicator of the subject’s ability to detect the gratings. These observations can provide guidance to clinicians who use preferential looking techniques to assess VA in infants.

Keywords: visual acuity • visual development • visual development: infancy and childhood