Visual Acuity within the Area Centralis and its Relation to Eye Movements and Fixation

Using an arrangement of the Ives visual acuity test with other special apparatus which is described, three subjects were studied as to the visual acuity of a central retinal region (including the fovea) with a radius of 85' or 0.42 millimeter from the axis of fixation. A uniform sensory gradient in the light adapted eye was shown to exist, the visual acuity decreasing rapidly but regularly in all directions without breaks or marked variations in rate of change at the margins of any known anatomical areas. The gradient continued to the very center of the retina. The horizontal and vertical meridians showed different rates of decrease of visual acuity. The results support the view that the sensory gradient is the basic factor in eye movements and fixation. From the Department of Physiology, Stanford University.