The role of the random dot Stereo Butterfly test as an adjunct test for the detection of constant strabismus in vision screening.

Background A goal of vision screening is the detection of amblyopia risk factors, including strabismus. The random dot Stereo Butterfly test requires no instruction, has a simple pass/fail response with no monocular clues, and is easily administered. The purpose of this study was to determine whether this test could be used as a cost-effective and reliable component of preschool vision screening. Methods The Stereo Butterfly was presented to children with no previous history of ocular problems or treatment. The test was presented with the use of polarized glasses at a 16-inch testing distance. A "pass" was recorded if the patient reported seeing a butterfly; a "refer" was denoted otherwise. Vision and motility measurements were recorded, and the patient underwent a complete eye examination with cycloplegic refraction. Results A total of 281 children 3 to 6 years of age were tested: 221 children passed the test. Of those who passed, 7 (3.2%) had intermittent strabismus, 1 had a small-angle constant strabismus, 60 failed screening for constant strabismus (of whom 24 [40%] had constant strabismus), and 6 were false-negative results. The sensitivity of the Stereo Butterfly for detecting constant strabismus was 96%; the specificity, 86%. Conclusions The Stereo Butterfly test may be a valuable adjunctive tool in vision screening programs for the detection of manifest strabismus because it is easy to administer and effectively detects constant strabismus. It has a high specificity for detection of constant strabismus but, if used alone, the low positive predictive value would allow for many false-positive results.