The relative effectivity of foveal and parafoveal stimuli in eliciting fusion movements has been evaluated by measuring the maximum amount of adduction which can be elicited by such stimuli. It was concluded that the amplitude of adduction declined precipitously as the stimuli were presented to more and more eccentric retinal regions.1
Figure 1 illustrates the type of targets used to elicit adduction of the left eye. When duction at the fovea is being tested, the right eye fixates the white dot in the center of the rectangle shown in the upper right half of Fig 1. When duction elicited by extrafoveal stimuli is being measured, the right eye fixates the white dot shown in the lower half of Fig 1. The centers of the rectangles presented to both the right and the left eyes are located at either 0, 0.25, 2, or 4 degrees to the right of the
LUDVIGH E, McKINNON P. Relative Effectivity of Foveal and Parafoveal Stimuli in Eliciting Fusion Movements of Small Amplitude. Arch Ophthalmol. 1966;76(3):443–449. doi:10.1001/archopht.1966.03850010445027
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