Patients have two eyes!: binocular versus better eye visual field indices

To test the hypothesis that better eye measures overestimate binocular visual field (VF) defect severity in glaucoma.

Humphrey VFs (24-2 SITA standard) from 67 consecutive patients with glaucoma were retrospectively examined (mean age, 65 years; range, 31-88 years). The better mean deviation (MD) from the two eyes was recorded (better eye MD). Binocular integrated visual field (IVF) was constructed for each patient by merging corresponding sensitivity values from monocular VF. An IVF MD was calculated from the average of total deviation values in the IVF. The differences between better eye MD and IVF MD were assessed.

The average IVF MD was significantly better than the average better eye MD (mean difference, 1.3 dB; 95% confidence interval [CI], 1.0-1.7 dB; P < 0.001). Twenty-four percent of patients had an IVF MD that was at least 2 dB healthier than the MD in the better eye (95% CI, 14%-34%). The size of the differences between better eye and IVF MD was significantly associated with the severity of VF defect (P < 0.001; R² = 0.44).

Monocular measures, such as better eye MD, can give the impression that a patient's VF loss is more degraded than it might be under binocular viewing. This effect is more pronounced in patients with advanced VF defects. The IVF offers a rapid assessment of a patient's binocular VF severity without extra testing.