Distance stereopsis as a screening device

Purpose: To determine the efficacy of distance stereotesting as a screening device. Methods: Distance stereoacuity using the global Random Dot and con tour Circle test of the Mentor BVAT II-SG computerized testing system was m easured for 216 patients, ages 6 to 18 years, before the clinical examinati on. Patients were classified into pass/fail groups in the areas of refracti ve error change (REC), ocular deviation (DEV), visual acuity (VA), and all three together (EXAM). Legitimate cutoff scores were obtained when patients were classified as 'pass' as follows: REC if the change was 0.50 D or less in sphere or cylinder relative to the habitual correction or to emmetropia if no habitual correction; DEV if there was no heterophoria or strabismus at distance (criteria of heterophoria of < 6 prism diopters and heterophori as of any magnitude were also tested); VA if the acuity at distance was bet ter than or equal to 20/25 in the poorer eye and better than or equal to 20 /20 in the better eye; EXAM if they were pass in REC, DEV, and VA. Optimal pass/fail cutoff values for the stereopsis measurements were determined by finding the maximum X-2 value from contingency tables constructed using pas s/fail levels for the screening test at each of the observed levels. Result s: The pass rates for REC, DEV, VA, and EXAM were 45%, 72%, 42%, and 24%, r espectively. Patients passed the BVAT at the analytically determined optima l cutoff values of less than or equal to 120 sec are for global and less th an or equal to 30 sec are for contour stereopsis. The sensitivity and speci ficity for global stereopsis were 0.90 and 0.40 for REC, 0.89 and 0.30 for DEV, 0.93 and 0.51 for VA, and 0.87 and 0.63 for EXAM. For contour stereops is, the corresponding values were 0.85 and 0.42, 0.89 and 0.34, 0.91 and 0. 53, and 0.84 and 0.62. Conclusion: Distance stereotesting is highly sensiti ve to small refractive error changes, heterophorias and strabismus, visual acuities < 20/25, or any of the three. Global stereopsis is only slightly b etter than contour stereopsis at classifying patients. Distance stereotesti ng has potential as an effective screening test.