sensory fusion

Sensory fusion is the unification of visual excitations from corresponding retinal images into a single visual percept.¹ The visual areas of the cerebral cortex integrate two similar images, one from each eye, and the fusion may be central, at the foveae, or peripheral, outside them.²

The stimulus to sensory fusion is the excitation of corresponding retinal elements, and both the central and the peripheral retina contribute fusible material.¹ The two images must also be sufficiently similar in size, brightness and sharpness, so unequal images are a severe sensory obstacle to fusion.¹ Fusion can survive a central visual deficit in one eye, but peripheral fusion is essential to binocular single vision and may be affected by advanced field loss in glaucoma or by pituitary lesions.²

Sensory fusion is essential for the highest degree of stereopsis, yet lower degrees of stereopsis can occur without it, as in microtropia.¹ Fusion also does not guarantee stereopsis, because some patients readily fuse similar targets and may have normal fusional amplitudes yet have no stereopsis.¹ Motor fusion is the separate ability to hold the eyes aligned for bifoveal fixation, and retinal image disparity drives it through the fusional vergences.²