Testing stereopsis in the preschool child: is it clinically useful?

The evaluation of stereoacuity should provide an unambiguous assessment of binocular function in infants and young children. Unfortunately, clinical measures of stereopsis in these young patients often result in stereotheresholds poorer than the criteria suggested to differentiate normal from anomalous binocular vision. Thus, two experiments were conducted to determine whether the large stereothresholds frequently demonstrated on tests designed for young children are diagnostic of normal binocular function in preschool children. The first experiment investigated the salience of the monocular cues in the Lang and Frisby stereotests in normal preschool children (2 to 5 years old). None of the children who passed either the Frisby or the Lang stereotest under binocular conditions were able to pass either test monocularly, even after passing the test binocularly. In the second experiment, preschool children with abnormal binocular vision were tested with the Lang and Frisby stereotests to determine if large disparities (730 to 800 seconds of arc [arcsec]) could be passed without normal binocular vision. None of the children with strabismus passed either stereotest. However, two children with anisometropia passed the Frisby test and one of these children also passed the Lang test. These results suggest that in the absence of other clinical findings to the contrary, the demonstration of gross stereopsis with either the Frisby (730 arcsec) or Lang (733 or 800 arcsec) test in the preschool child implies normal binocular function. Thus, clinical tests of stereopsis for infants and preschool children, like those used routinely for adults, can provide evidence of binocular function without approaching stereothreshold.