Monocular Clues in Seven Stereotests

Abstract

Purpose: There have been numerous reports with evidence detailing the presence of non-stereoscopic or “monocular”clues in commonly used stereoacuity tests. The purpose of this study was to quantify the influence of monocularclues in the Titmus, Randot®, Randot® Special Edition, Randot® Preschool, Lang, Lang II, and Frisby stereoacuitytests. Stereoacuity testing is typically performed and/or interpreted by eye care professionals and other health/occupational professionals. Methods: Two separate prospective studies were conducted. The first assessed the monocular responses of 100subjects aged 8 to 67 with normal stereoacuity, and no previous exposure to any of the seven tests administered.The second assessed the monocular responses of 33 subjects aged 8 to 65 with longstanding, manifest, horizontalstrabismus of 20 prism diopters or greater, on the aforementioned stereotests. Results: Monocular clues were found to be present for the normal group on the Titmus (61%), Randot® (6%), Randot®Special Edition (5%), Randot® Preschool (7%), Lang (13%), and Lang II (37%). Monocular clues were found to be presentfor the strabismic group on the Titmus (100%), Randot® (9%), Randot® Special Edition (9%), Randot® Preschool (12%),Lang (3%), and Lang II (27%). There was no monocular identification for either group on the Frisby stereotest, butthere was minimal binocular identification by a subject with manifest strabismus. Conclusion: Monocular clues were present for both the normal and strabismic group on 6 of the 7 stereotestsinvestigated. Based on these findings the authors conclude that caution must be used when interpreting patientresponses on the 7 aforementioned stereotests.