Using an open-source tablet perimeter (Eyecatcher) as a rapid triage measure for glaucoma clinic waiting areas

Abstract

Background: Glaucoma services are under unprecedented strain. The UK Healthcare Safety Investigation Branch recently called for new ways to identify glaucoma patients most at risk of developing sight loss, and of filtering-out false-positive referrals. Here, we evaluate the feasibility of one such technology, Eyecatcher: a free, tablet-based 'triage' perimeter, designed to be used unsupervised in clinic waiting areas. Eyecatcher does not require a button or headrest: patients are simply required to look at fixed-luminance dots as they appear.

Methods: Seventy-seven people were tested twice using Eyecatcher (one eye only) while waiting for a routine appointment in a UK glaucoma clinic. The sample included individuals with an established diagnosis of glaucoma, and false-positive new referrals (no visual field or optic nerve abnormalities). No attempts were made to control the testing environment. Patients wore their own glasses and received minimal task instruction.

Results: Eyecatcher was fast (median: 2.5 min), produced results in good agreement with standard automated perimetry (SAP), and was rated as more enjoyable, less tiring and easier to perform than SAP (all p<0.001). It exhibited good separation (area under receiver operating characteristic=0.97) between eyes with advanced field loss (mean deviation (MD) < -6 dB) and those within normal limits (MD > -2 dB). And it was able to flag two thirds of false-positive referrals as functionally normal. However, eight people (10%) failed to complete the test twice, and reasons for this limitation are discussed.

Conclusions: Tablet-based eye-movement perimetry could potentially provide a pragmatic way of triaging busy glaucoma clinics (ie, flagging high-risk patients and possible false-positive referrals).

Keywords: diagnostic tests/Investigation; field of vision; glaucoma; psychophysics.

Figure 1

Eyecatcher. (A) Apparatus and stimuli. The tablet screen measured 26x17.3 cm (26.6°x17.9° when viewed at 55 cm). The eye-tracker is magnetically attached to the base of the tablet. (B) Test grid, in degrees visual angle. (C) Example output. Green areas indicated hits (target looked at). Red areas indicate misses (target not looked at). (D) Example test sequence. on each trial a single, fixed-intensity light spot was presented, and the computer determined whether or not an eye-movement was made towards it (see online supplementary text for technical details). Note that stimuli were presented relative to the current point of fixation, and so could appear at any screen location throughout the course of the test. See online supplementary video S1 for a recording of an example test sequence.

Figure 2

Individual VF assessments for (A) all 11 new referrals (none of whom was believed to have glaucoma), and (B) 11 randomly selected follow-up patients (all with an established diagnosis of glaucoma). In each case, the HFA grey scale is given on the left and the two corresponding Eyecatcher heatmaps are given on the right (NB: Eyecatcher was performed twice). Red markers highlight regions of the HFA where VF loss was greater than the magnitude of the Eyecatcher stimulus (–6 dB). If concordance between the two tests was perfect, then red markers in the HFA should appear as red shaded regions on the Eyecatcher heatmap. Note that new referral ID 9 was non-glaucomatous, but was a cataract patient with a generalised loss of sensitivity across the visual field (MD = −5.6 dB). MD, mean deviation; SAP, standard automated perimetry; VF, visual field.

Figure 3

Agreement in overall sensitivity between Eyecatcher (mean hit rate) versus SAP (HFA mean deviation (MD)). Each data point represents a single test/eye from a single patient. Each patient completed Eyecatcher twice, and the data from each run are given separately (circles for run 1, squares for run 2). The solid line shows line of best fit (polynomial spline fit). Any data points falling in the top left region would be considered a false-negative result (good performance on Eyecatcher, despite substantial field loss). SAP, standard automated perimetry.

Figure 4

Bland-Altman plot, showing test–retest repeatability for Eyecatcher (mean hit rate). Grey shaded regions show 95% CIs for the mean. Dashed red lines indicate the 95% limits of agreement. COR, coefficient of repeatability.