An Alternative Vision Test Stimulus: Orientation-Performance Isotropy Confirmed in Central Fixation for an Angular Broken Ring Test Target

Ophthalmologists and optometrists use charts displaying the Landolt broken ring stimulus instead of letters when testing the vision of specific patient groups. However, a degree of performance inequality versus stimulus orientation has been claimed in association with the use of the classic circular broken ring design. In recent years an angular version of the stimulus has found application in several clinical and vision-related studies. The present investigation was undertaken to assess whether testing with this alternative angular optotype design has any influence on orientation-performance anisotropy in central fixation. Ten normally-sighted subjects undertook an automated four-alternative forced-choice visual discrimination task under monocular foveal viewing conditions. Their error (orientation misidentification) performance was recorded in response to a randomised sequence of high-contrast single, variously sized, four-alternative orientation angular broken ring stimuli. Having first weighted the grouped error scores to counter orientation heterogeneity in stimulus presentation, statistical analysis indicated equality of performance across the four orientations of presentation. Subsidiary analysis failed to reveal any evidence of a systematic error bias associated with stimulus angular subtense. The angular design of the broken ring optotype tested here appears to have promoted isotropic orientation performance in central fixation for this group of normally-sighted adult subjects.