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Steven C Dakin, Soheil Mohammadpour Doustkouhi, Hannah Kersten, Philip RK Turnbull, Jinny Yoon, Helen Danesh-Meyer; Measuring visual field loss in glaucoma using involuntary eye movements. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2468.
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Diagnosis and monitoring of glaucoma depends on perimetry to assess the functional visual field (VF). Such procedures are time-consuming, and reliant on patients' ability/willingness to make subjective judgements. Here we describe an alternative approach that uses involuntary eye movements to quantify the integrity of the VF. Specifically, since human optokinetic nystagmus (OKN) is known to depend on the spatial extent of stimuli we performed an observational clinical study that asked if OKN is a reliable indicator of the extent of glaucomatous VF loss.
We tested 41 patients with asymmetric VF loss from primary open angle glaucoma (POAG). Inclusion criteria were a previous diagnosis of POAG, and a difference in visual field index (VFI) across the eyes ≥10%. We excluded patients with other ocular or neurological disease, significant media opacity, or who were unable to maintain attention during testing.Patients underwent an ophthalmologic examination including static automated perimetry (HFA II), biomicroscopy and OCT. We measured OKN using a series of 2s movies consisting of spatial frequency (SF) bandpass filtered noise (1.3 c/deg) drifting horizontally at 10 deg/s. Stimuli were presented monocularly (to both eyes) at contrasts between 3% and 100%. Eye movements were recorded at 90 Hz using a consumer-grade eyetracker (Tobii 4c). We used fixation data to estimate OKN-gain (our outcome measure): speed of slow-phase tracking eye-movements relative to target speed.
OKN-gain was lower when patients used their more affected eye compared to their less affected eye (Fig 1A; t-test over all contrasts, p<0.00001). This difference was pronounced at intermediate levels of contrast (6-25%). Differences in OKN-gain across eyes were correlated with difference in VFI across eyes (e.g. for a 12.5% pattern, R=0.61, p=0.00002, Fig 1B) in all but the lowest (3%) contrast condition.
Glaucomatous visual field loss is associated with slower tracking during OKN: the greater the loss, the slower the tracking. As a means of quantifying field loss, OKN-tests have the potential to overcome several shortcomings of perimetry, since they are not dependent on patients maintaining fixation, or making reliable subjective judgements.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Fig 1A. OKN-gain as a function of contrast for one patient. B. Difference in log(OKN gain) across the eyes as a function of difference in VFI across the eyes
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