Visual fields in glaucoma: Where are we now?

Which glaucoma patients benefit from 10-2 visual field testing? Proposing the functional vulnerability zone framework

CLINICAL RELEVANCE

A method for determining 10-2 deployment in glaucoma with the goal of detecting additional visual field sensitivity for the purpose of functional monitoring is proposed.

BACKGROUND

To provide a pilot method for determining when to deploy the 10-2 visual field (VF) test grid in glaucoma by characterising the 'functional vulnerability zone'.

METHODS

The cross-sectional 24-2 (central 12 locations) and 10-2 VF results from 133 eyes of 133 glaucoma subjects were used to describe the central Hill of Vision using VF sensitivity. The 'volume' (defined using arbitrary units, A.U.) under the Hill was calculated. A greater A.U. on the 10-2 indicated a functional vulnerability zone (FVZ), signifying additional clinical dynamic range for potential future monitoring. The main outcome measures were calculated A.U. and 24-2 factors which were significantly related to A.U. differences between 24-2 and 10-2.

RESULTS

Over 55% of patients had an FVZ (A.U. greater using 10-2). Several 24-2 features (worse mean deviation, worse central 24-2 mean defect, and a higher proportion of defective locations) were significant in the FVZ cohort compared to non-FVZ. 24-2 mean deviation levels at which 10-2 may be favoured were low at -3.16 to -3.62 dB. Specifically, 5 or more defective central 24-2 test locations were associated with an FVZ. Subjects exhibiting a less severe defect on the 10-2 were more likely to have an FVZ, indicating its potential for future VF monitoring.

CONCLUSIONS

The authors propose several clinical markers, focussing on the 24-2, which can guide clinicians on when the 10-2 may have utility in glaucoma assessment. The authors provide a pilot reference spreadsheet for clinicians to visualise the likelihood of 10-2 utility in the context of an FVZ.

Comparing a head-mounted virtual reality perimeter and the Humphrey Field Analyzer for visual field testing in healthy and glaucoma patients

PURPOSE

To compare clinical visual field outputs in glaucoma and healthy patients returned by the Humphrey Field Analyzer (HFA) and virtual reality (Virtual Field, VF) perimetry.

METHODS

One eye of 54 glaucoma patients and 41 healthy subjects was prospectively tested (three times each in random order) using the HFA and VF perimeters (24-2 test grids). We extracted and compared global indices (mean deviation [MD] and pattern standard deviation [PSD]), pointwise sensitivity (and calculated 'equivalent' sensitivity after accounting for differences in background luminance) and pointwise defects. Bland-Altman (mean difference [Mdiff ] and 95% limits of agreement [LoA]) and intraclass correlation analyses were performed.

RESULTS

The VF test was shorter (by 76 s) and had lower fixation losses (by 0.08) and false-positive rate (by 0.01) compared to the HFA (all p < 0.0001). Intraclass correlations were 0.86, 0.82 and 0.47 for MD, PSD and pointwise sensitivity between devices, respectively. Test-retest variability was higher for VF (Mdiff 0.3 dB, LoA -7.6 to 8.2 dB) compared to the HFA (Mdiff -0.3 dB, LoA -6.4 to 5.9 dB), indicating greater test-retest variability. When using each device's underlying normative database, the HFA detected, on average, 7 more defects (at the p < 0.05 level) out of the 52 test locations compared to this iteration of VF in the glaucoma cohort.

CONCLUSIONS

Virtual Field returns global results that are correlated with the HFA, but pointwise sensitivities were more variable. Differences in test-retest variability and defect detection by its current normative database raise questions about the widespread adoption of VF in lieu of the HFA.