Purpose: The 10-diopter (D) fixation test is a useful test for detecting amblyopia in children without a manifest deviation and in whom a reliable visual acuity assessment is difficult. The 10 prism diopter is conventionally placed base down.
Methods: Seventeen children were studied over a 12-month period to determine 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 with unilateral ptosis, the prism should be held base up when performing the 10-D fixation test.