Diagnosis of amblyopia using the 10-diopter fixation test: A proposed modification for patients with unilateral ptosis

Purpose: The 10-diopter (D) fixation test is a useful test for detecting am blyopia in children without a manifest deviation and in whom a reliable vis ual acuity assessment is difficult. The 10 prism diopter is conventionally placed base down, Methods: Seventeen children were studied over a 12-month period to determin e the effect of prism orientation on the accuracy of the 10-D fixation test in children with unilateral ptosis. Results: Anomalous results were obtained in 4 of 17 patients with the prism held base up and base down. Conclusions: To prevent an erroneous diagnosis of amblyopia in children wit h unilateral ptosis, the prism should be held base up when performing the 1 0-D fixation test.