Background: Many studies have been performed on validity of different methods for Amblyopia screening and this one was designed to assess the reliability of the TNO test for that purpose.

Materials and Methods: This is a diagnostic value study. Visual acuity and stereo acuity of 100 patients with Amblyopia caused by refractive errors, strabismus with wide angle, or micro strabismus were measured and compared with the stereo acuity of 300 normal students using TNO test. Statistical analysis carried out to determine sensitivity, specificity, and diagnostic value. Then, positive and negative predictive values were calculated by considering 120 seconds of arc stereopsis as the cut off point.

Results: Ninety five percent of students had good stereopsis (120 second of arc or better). Patients group showed limited stereopsis. The most common cause of amblyopia in patients group was refractive errors (62%). The most defective stereopsis was clearly associated with wide angle strabismus. In this study TNO test had missed (underestimated) 8% of cases with Amblyopia and had 5% over referral rate but had sufficient power to detect patients with moderate to severe Amblyopia. Its sensitivity and specificity were 85.9% and 97.2% respectively.