Introduction: In spite of its well- known flaws, the Titmus test is still the most commonly available and frequently utilized stereotest worldwide. Detecting stereopsis in the patient with small- angle strabismus is an important part of the sensorimotor exam. Because these patients often have only gross stereopsis, stereoacuity may have to be evaluated with the House Fly plate alone. This study evaluates an alternative method of presentation designed to decrease the false positive rate of the Titmus Fly test. Methods: A group of orthotropic volunteers with normal binocular vision, a group of patients with small angle strabismus, and a group of patients whose angle of strabismus was large enough to preclude stereopsis were tested with the Titmus Fly using two different presentations and compared. Results: The sensitivity of the Titmus Fly test was 79, but specificity was only 26 due to the large number of false positive responses detected with the modified presentation. Patients with childhood- onset strabismus who have been repeatedly exposed to this test over many visits were particularly vulnerable to overestimation of stereoacuity. Conclusion: If the Titmus fly test is the only stereoacuity measure that can be used due to the presence of manifest strabismus, modifying the presentation of the test plate with this method will improve accuracy and precision of results.
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