Quantification of Agreement and Variability of a Newly Developed Visual Field Algorithm With the Reference Standard

Quantification of Agreement and Variability Characteristics of a Newly Developed Visual Field Algorithm With the Reference Standard: an Observational Study

This study aims to compare two types of visual field test; retinal sensitivity values obtained with the reference standard Swedish Interactive Thresholding Algorithm (SITA) of the standard visual field test and with a newly developed test algorithm. The new test is a visual field test presented on a flat-panel monitor and has two modes: differential light sensitivity (DLS; equivalent to the standard visual field test) and the Moorfields Motion Displacement Test (MMDT). DLS sensitivity and DLS measurement variability will be determined and compared between the SITA algorithm of the standard visual field test and the new visual field test on the flat-panel monitor. The measurement variability of the MMDT will be quantified.

The long-term goal is to reduce test variability below that observed in SITA by 20%, whilst producing comparable measurements (contrast threshold values) for comparable test duration.

Standard Automated Perimetry (SAP) is currently the standard test for screening and monitoring visual loss owing to glaucoma. This test requires the patient to sit at a machine, looking at a central light and pressing a button whenever small spots of light appear in the peripheral vision. Traditionally these spots of light are projected into a bowl (concave surface), but more recently, computer monitors have been used. Other techniques are also now available such as the Moorfields Motion Displacement Test, where patients are required to press a button each time they see a vertical line on the screen wiggle. This test has been shown to have advantages over SAP, namely, to be tolerant to the effects of cataract and refractive error.

In clinical settings, the Humphrey Visual Field Analyzer (Zeiss Meditec) is the most used visual field test in the UK. It employs a SAP strategy coupled with the Swedish Interactive Thresholding Algorithm (SITA), which is used to derive retinal sensitivity. Visual field measurements are very variable, requiring many tests over a long period to determine the extent of vision loss. In addition to the inconvenience caused to patients, the contribution of these many tests to the financial burden on the NHS is increasing with the growing aging population. As glaucoma is a chronic disease, patients need lifelong monitoring, requiring multiple tests and clinic visits. To address these unmet needs, the investigators have developed a new algorithm that can be used to monitor glaucoma.

The investigators wish to carry out a study, which will allow them to compare agreement between SITA and a newly developed test algorithm. Measurement variability will be determined and compared between strategies. The long-term goal is to reduce test variability and the test time observed in SITA, whilst producing comparable contrast threshold values.

Inclusion Criteria:

• Best corrected visual acuity of 6/12 or better in the test eye
• No ocular morbidity other than glaucoma; early lens opacity and prior cataract surgery are acceptable

Healthy eyes

• Central 30° visual field within normal limits on the 24-2 test (MD within 95 % CI and glaucoma hemifield test within normal limits).

Glaucoma eyes

• More than two reliable visual fields with reproducible defects
• IOP < 30 mmHg

Exclusion Criteria:

• Any systemic disease which is likely to affect visual performance in a short period of time
• Inability to steadily fixate on the test (e.g. individuals who have nystagmus or macular degeneration)
• Eyes with unreliable visual fields (defined as false positive responses >15%)