Stereo tests as a screening tool for strabismus: which is the best choice?

PURPOSE To compare four stereo tests (Lang I, Lang II, Titmus, and TNO) and assess their effectiveness. The main focus of this study is to identify the most useful stereo test as a challenging tool in the screening of strabismus. PATIENTS AND METHODS A total of 143 Caucasian subjects, 74 males (52%) and 69 females (48%), aged between 4 years and 78 years (mean age 19.09±15.12 years) were examined at our Strabismus Service (Scientific Institute San Raffaele Hospital, Milan, Italy) and included in this observational cross-sectional study. Subjects recruited in this study were either affected by strabismus, including microstrabismic patients, or healthy volunteers. Subjects affected by ophthalmological diseases, other than strabismus, were excluded. All patients underwent both ophthalmological and orthoptic examination, including stereo tests, Hirschberg Corneal Light Reflex Test, Worth Four-Dot Test, the 4 Prism Diopter Base-Out Test, Cover Testing, Bruckner Test, visual acuity, automated refraction under 1% tropicamide cycloplegia and thereafter, posterior pole evaluation. RESULTS All data were processed using the IBM SPSS Statistics, Version 2.0, to perform all statistical calculations. The main finding of this study is that Lang I stereo test achieved the highest sensitivity (89.8%) and specificity (95.2%) in detecting strabismus, including microstrabismus as well, compared to all the other stereoacuity tests. Furthermore, Lang I is the stereo test with the highest positive predictive value and negative predictive value, both greater than 90%. CONCLUSION The stereo test with the highest sensitivity, specificity, positive predictive value, and negative predictive value is Lang I. These results suggest its applicability as a screening test for strabismus in people older than 4 years.