Threshold perimetry of each eye with both eyes open in patients with monocular functional (nonorganic) and organic vision loss

To report a novel binocular perimetry test to identify monocular functional vision loss.

In a prospective study, 10 patients with monocular functional vision loss, 10 patients with monocular organic vision loss, and 10 normal subjects were tested using a Humphrey automated perimeter attachment that performs central threshold perimetry of both eyes in a single test. First, patients were tested after being told their "good" (unaffected) eye was being tested; this was followed by a second identical test said to be on the "bad" (affected) eye. Two measurements were calculated for each subject: the functional component (deltaF), defined as the difference (in dB) between the mean threshold of the first and second tests, and the organic component (deltaO), the difference (in dB) between the mean threshold of the unaffected and affected eyes.

Patients with monocular functional vision loss produced lower thresholds when they thought their affected eye alone was being tested but little intereye difference (mean deltaF +/- SD = 17.35 +/- 7.50 dB; mean deltaO = 0.01 +/- 1.40 dB). Patients with monocular organic vision loss had little difference between tests and lower thresholds in their affected eye (mean deltaF = 0.84 +/- 1.15 dB; mean deltaO = 9.01 +/- 4.71 dB). Normal subjects demonstrated little intertest or intereye differences (mean deltaF = -0.15 +/- 0.78 dB; mean deltaO = -0.05 +/- 0.51 dB).

This perimetry method effectively distinguished between normal subjects, patients with monocular functional vision loss, and patients with monocular organic vision loss.