Panum’s area

Panum’s area is an area in the retina of one eye, any point of which gives a single percept when stimulated together with a single point in the retina of the other eye. Panum’s area defines the range of disparities that allows fusion and stereopsis.¹ In space, the matching region is a narrow band in front of and behind the horopter. Objects in that band are seen singly and in depth.²

The fovea of one eye corresponds with a small area centered on the fovea of the other eye, and every other retinal point corresponds with a small area in the fellow eye.³ Because of this point-to-area correspondence, an eye can deviate slightly before its image leaves Panum’s area and diplopia appears.³ The small deviation from fixation that produces no diplopia is called fixation disparity.³

Panum’s areas are small and horizontally oval.³ In the classic measurements, the horizontal extent is 6 to 10 minutes of arc near the fovea and around 30 to 40 minutes of arc at 12 degrees from the fovea.² More recent work with moving random-dot stereograms shows that disparities as large as 2 to 3 degrees can be fused.² Measured size varies with retinal eccentricity and with the spatial and temporal properties of the stimulus, so Panum’s area is better thought of as a phenomenon of cortical processing than as a fixed entity.³