Behavior of visual field index in advanced glaucoma

Area of Science:

• Ophthalmology
• Optometry
• Visual Science

Background:

• The Visual Field Index (VFI) is a key metric for assessing glaucoma progression.
• Algorithm changes in visual field (VF) analysis, specifically from pattern deviation probability plot (PDPP) to total deviation probability plot (TDPP), can impact VFI calculations.
• Understanding these impacts is crucial, especially when mean deviation (MD) crosses critical thresholds like -20 decibels (dB).

Purpose of the Study:

• To quantify the magnitude of VFI change resulting from the shift between PDPP and TDPP algorithms.
• To investigate this change specifically when the mean deviation (MD) of visual fields crosses the -20 dB threshold.

Main Methods:

• A retrospective study analyzed 37 stable glaucoma eyes where MD crossed -20 dB.
• VF pairs were selected with MDs just above and below -20 dB.
• VFI changes and their correlation with the number and eccentricity of points in probability plots were evaluated. Control data from MD crossing -10 dB was also analyzed.

Main Results:

• VFI change ranged from 3% to 33% (median 15%) when MD crossed -20 dB, compared to 1% to 8% (median 4%) when MD crossed -10 dB.
• The number of points with normal threshold sensitivities in PDPP versus TDPP significantly influenced VFI change (R² = 0.65).
• Eccentricity of these points further explained VFI change (R² = 0.81).

Conclusions:

• The decrease in VFI when MD crosses -20 dB exhibits significant variability.
• This variability necessitates careful consideration when utilizing VFI in clinical practice and research settings.