The Precision Of Five Year Forecasts Of The Visual Field Index (vfi) Using Series Of Monocular And Binocular Visual Fields

Abstract

 

Purpose:

 

To compare properties of the Visual Field Index (VFI) as applied to series of binocular and monocular visual fields (VF).

 

Methods:

 

Series of ten consecutive VFs (Humphrey 24-2 Full-threshold) spanning on average 3.6 (SD: 0.75) years from 66 eyes from 33 glaucomatous patients (mean age: 64.0 [SD: 8.2] years) were retrospectively examined. The VFs of both eyes were merged to produce the ‘integrated VF’ using the ‘better sensitivity’ method (Asaoka et al. ARVO 2010). A VFI score of the ‘integrated VF’ (Binocular VFI) was estimated following the method described in Bengtsson & Heijl (2008). The VFI of the better eye was also calculated (Monocular VFI). ‘Forecasts’ of VFI were calculated for each patient by projecting linear regression to a 5 year time point after the last VF as depicted on the Humphrey Guided Progression Analysis (GPA) VFI Bar graphical output. A measure of the precision of the forecast was calculated as the width of the 95% confidence limit (CL) of this prediction for each individual: this can be interpreted as a range of values that the predicted VFI might likely take 5 years from the most recent clinical visit given the variability in the series of data.

 

Results:

 

In this sample of patients, average width of the 95% CL for the 5 year prediction for the Monocular and Binocular VFI was 23% (SD: 17%) and 13% (SD: 10%) respectively. These estimates of precision of the 5 year predictions were significantly different (P<0.001; paired Wilcoxon-test Non-Parametric test).

 

Conclusions:

 

Even when long series of VFs are available, 5 year extrapolation of VFI, as shown on the Humphrey GPA output, yields predictions that have only moderate precision. However, VFI predictions based on binocular measures have better precision than those based on monocular measures.

 

Keywords: visual fields • binocular vision/stereopsis • quality of life