Horizontal Lang two-pencil test as a screening test for stereopsis and binocularity

Purpose: To assess the horizontal Lang two-pencil test as a bedside test to detect gross stereopsis. Materials and Methods: Eighty-four strabismic subjects divided into two groups based on the amount of deviation, and 40 normal subjects were studied. Sensory status examination including binocularity and stereopsis were evaluated with Bagolini, Titmus test and the Netherlands organisation for applied scientific research (TNO), Randot, synoptophore and horizontal Lang two-pencil test. Results: The subjects in the group with smaller deviation showed better performance on all the four stereo tests and over 90% demonstrated presence of fusion. When compared to TNO and Randot for determining presence of stereopsis, the horizontal Lang two-pencil test demonstrated sensitivity of 100% and 83.9%, specificity of 77.8% and 73.7%, and negative predictive value of 100% and 100% respectively. It also showed 100% specificity as a test for binocularity when compared with the Bagolini striated glass test. Conclusion: Horizontal Lang two-pencil test, an easily performed test with a high sensitivity and negative predictive value can be used as a screening test to detect gross stereopsis and binocularity.