Development of stereopsis depends upon contrast sensitivity and spatial tuning.

Various binocular functions such as disparity vergence, and stereopsis develop rapidly during the third to fifth month of life. This time frame coincides with the rapid postnatal development of visual acuity, contrast sensitivity and possibly the tuning of spatial channels. Recent studies of adult stereopsis reveal that small disparities near the stereo threshold are processed within spatial channels tuned above 2.5 cycles/deg. Sensitivity to these higher spatial frequencies develops during the 3-5 months of life. Adult studies also reveal that larger disparities are processed by spatial channels tuned to lower spatial frequencies. Tuning of these low spatial frequency channels may not be present until 3 months of age. Lack of spatial tuning prior to 3 months is predicted to be associated with a lack of disparity tuning as well as an inability to ignore false disparities in ambiguous or redundant stimuli such as random dot stereograms. These observations suggest that refractive anomalies such as anisometropia that limit high frequency spatial resolution and binocular integration can present a major obstacle to the postnatal development of binocular vision.