The polarized three-dot test.

A new binocular sensory test was designed using polarizing filters. The polarized three-dot test (P3D) subtends the same visual angle as the Worth four-dot test (W4D). Sensory testing was performed at distance and near in 100 patients using the W4D and P3D tests. Every patient reliably completing the W4D test also completed the P3D test. Twelve patients failed to complete both tests. Fifteen patients could not reliably complete the W4D test but were able to perform the P3D, thus increasing the interpretable response rate from 73% for the W4D test to 88% for the P3D (chi square, p less than .0001). In every case but one, fusion by W4D testing was also found by the P3D test. In addition, the P3D identified 19 cases of fusion not found by W4D testing. The results suggest that the P3D test is superior to the W4D test in the clinical assessment of central and peripheral fusion.