Five-year forecasts of the Visual Field Index (VFI) with binocular and monocular visual fields

In clinical care, visual field (VF) damage is assessed using monocular VF testing, yet patients perceive the world binocularly. This study was conducted to compare 5-year forecasts for the Visual Field Index (VFI) generated from series of binocular and monocular VFs. Series of ten consecutive VFs (Humphrey 24-2 Full-threshold) spanning on average 3.7 (SD: +/- 0.8) years from 60 eyes of 30 glaucomatous patients were retrospectively examined. The VFs of both eyes were merged to produce the integrated VF and its VFI score (Binocular VFI) was estimated. Forecasts of binocular and monocular VFIs were calculated for each patient by projecting the fitted linear regression 5 years ahead from the last VF following the method on the Humphrey Guided Progression Analysis (GPA) print-out. The precisions of the forecasts were calculated as the width of the 95 % prediction limit (PL). The mean 5 year forecast for binocular VFIs was 92 % (SD: 11 %), which was significantly higher than forecasts from right and left eyes (79 % [SD: 19 %] and 82 % [SD: 16 %] respectively; P < 0.05). The width of the 95 % PL for 5-year predictions with monocular VFIs (mean right eye: 29 % [SD: 19 %] and mean left eye: 27 % [SD: 16 %]) were significantly larger than that of the binocular VFI (mean: 12 % [SD: 7 %]; P < 0.05). Five year forecasted VFI values using binocular measures return significantly better values, and can be made with greater confidence than those based on monocular measures. In turn, forecasts of a patient's binocular VFI might be more relevant to estimating the patient's future functional VF.