Using a binocular field expander on a wide-field search task.

Five patients with constricted visual fields and good central acuity were fitted with an experimental binocular field expander. They undertook a laboratory visual search task in a stationary horizontal 90 degree field with and without the device. Four of five patients adapted relatively quickly to the inherent optical distortions of the field expander. When this binocular aid was worn search efficiency improved significantly with practice; search time was highly correlated (r = -0.92; p less than 0.01) with information channel capacity in the larger visual field.