Standard automated perimetry using size III and size V stimuli in advanced stage glaucoma: an observational cross-sectional comparative study

Abstract

Objectives: In this study, we sought to evaluate the extent of further visual field that could be assessed when using stimulus size V in standard automated perimetry compared with size III in advanced stage glaucoma and whether cut-off values could be determined for when to switch from size III to size V.

Design: Prospective cross-sectional study.

Setting: Single-centre outpatient eye clinic in India (New Delhi).

Participants: Advanced stage glaucoma defined as stages 3-4.

Intervention: Central static perimetry with Octopus 900 G programme (size III stimulus dynamic strategy) and low vision central programme (size V stimulus dynamic strategy).

Primary and secondary outcome measures: Visual field assessment for right and left eyes with both sizes III and V were undertaken within one clinic visit.

Results: We recruited 126 patients (170 eyes). Mean patient age at assessment was 55.86 years (SD 15.15). Means (SD) for size III versus size V, respectively, were 6.94 dB (5.58) and 12.98 dB (7.77) for mean sensitivity, 20.02 dB (5.67) and 19.22 dB (7.74) for mean deviation, 5.89 dB (2.29) and 7.69 dB (2.78) for standard loss variance and 3.32 min (1.07) and 6.40 min (1.43) for test duration. All except mean deviation were significantly different between size III and V tests.

Conclusion: Useful visual field information was obtained with size V stimuli which allowed continued monitoring of these patients that was not possible with size III. Increased test duration, standard loss variance and mean sensitivity were found with size V, as expected, given that more visual responses were obtained with the increased target size. A switch from size III to V may be considered when mean sensitivity reaches 10 dB and/or mean deviation reaches 18 dB.

Keywords: glaucoma; neuro-ophthalmology; ophthalmology.

Figure 1

Illustrative results of static size III versus size V perimetry. (A) G1 static perimetry with size III, left eye. (B) LVC static perimetry with size V, left eye. Static perimetry (using size III) results show a severely restricted visual field while static perimetry (using size V) results display better temporal visual field and inferonasal visual field. LVC, low vision central; MD, mean deviation; MS, mean sensitivity; IOP, intra ocular pressure; OS, left eye; RF, reliability factor; VA, visual acuity.

Figure 2

Mean sensitivity and mean deviation comparisons—primary analysis of all eyes. (A) Mean sensitivity. Straight line is the linear regression line; curved line is the loess regression curve. Comparisons generally show clustering where mean sensitivity is close to 0 dB, that is, worst visual field. There is a ‘floor’ effect with size III, yielding many zeros, while size V gives, for most, larger values. The linear regression line and loess regression curve show large correlation for size V (r²=0.731, p<0.0001). The loess point of inflection (value taken from the y axis) is approximately 4–6 dB. (B) Mean deviation. Straight line is the linear regression line; curved line is the loess regression curve. The linear regression line and loess regression curve show large correlation for size V (r²=0.735, p<0.0001). The loess point of inflection (value taken from the y axis) is approximately 22–24 dB. loess= locally estimated scatterplot smoothing.

Figure 3

Mean sensitivity and mean deviation comparisons—sensitivity analysis of worst eyes. (A) Mean sensitivity. straight line is the linear regression line; curved line is the loess regression curve. Comparisons generally show clustering where mean sensitivity is close to 0 dB, that is, worst visual field. There is a ‘floor’ effect with size III, yielding many zeros, while size V gives, for most, larger values. The linear regression line and loess regression curve show large correlation for size V (r²=0.678, p<0.0001). The loess point of inflection (value taken from the y axis) is approximately 3–5 dB.(B) Mean deviation. Straight line is the linear regression line; curved line is the loess regression curve. The linear regression line and loess regression curve show large correlation for size V (r²=0.687, p<0.0001). The loess point of inflection (value taken from the y axis) is approximately 22–24 dB. loess= locally estimated scatterplot smoothing.