Testing distance stereoacuity with the Frisby-Davis 2 (FD2) test

To develop a presentation protocol for the new Frisby-Davis 2 (FD2) distance stereoacuity test. Prospective data collection. Stereoacuity was tested monocularly and binocularly in 95 patients with a variety of strabismic and nonstrabismic conditions, using the FD2, employing a modified staircase procedure. The Preschool Randot Stereoacuity test and the near Frisby test were used to determine whether a patient was stereoblind. Under monocular conditions, 35 (37%) of 95 patients passed at least the largest disparity of the FD2 indicating a problem with monocular cues. The binocular protocol was then modified to include a monocular test phase. Using the new protocol, if a patient could achieve the same stereoacuity under monocular and binocular conditions, they were deemed to have no stereopsis. Testing 28 additional stereoblind patients using the new modified protocol revealed no false positives. The FD2 stereotest is a useful measure of distance stereoacuity, provided the presentation protocol accounts for monocular cues.