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Eye movements may be biomarkers for visual field damage in glaucoma
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Eye movements recorded while patients with glaucoma passively view images may potentially be used as biomarkers for visual field damage, according to researchers.
They also found that patients with between-eye asymmetric visual field loss exhibit systematically different eye movements in their worse eye when viewing images monocularly.
In this study, 15 patients with glaucoma with asymmetric vision loss viewed 120 images of natural scenes monocularly on a computer monitor.
Each image was viewed twice, once in the eye with better vision and once in the worse eye, and eye movements were recorded with an Eyelink 1000 (Sr Research, Ontario) eye tracker.
A novel eye tracking parameter was created, saccadic reversal rate (SRR), to understand the temporal dynamics of a scan path. The researchers hypothesized that that these movements would be particularly elevated when vision was impaired.
More traditional metrics such as saccade amplitude, fixation counts, fixation duration and spread of fixation locations were also analyzed.
In the worse eye, saccade amplitude and bivariate contour ellipse area (BCEA) were smaller, while SRR was greater.
Researchers found a significant correlation between intereye difference in BCEA and differences in mean deviation (MD) within asymmetric vision loss. Differences in SRR were associated with differences in visual acuity.
There was no statistically significant difference between eyes in fixation duration, fixation count, saccade velocity or scan path length, according to researchers. However, eyes with better vision made larger saccades, exhibited greater BCEA and lower SRR.
They found a significant association between the differences in SRR and differences in logMAR.
Between-eye differences in BCEA alone were a statistically significant predictor of between-eye differences in MD values: For every 1 dB difference in MD, BCEA decreased by an average of 6.2%, according to researchers.
SRR, the novel eye-movement summary measure, may be applied to analyze eye movements in patients with other ophthalmic or neurogenerative conditions, they said.
SRR was significantly greater in the worse eye, indicating that the worse eye exhibited more back-and-forth saccadic movements than the fellow, better eye, they wrote.
Researchers did not find a significant difference between the worse and better eye in terms of basic eye-movement metrics such as saccade count, fixation count, fixation duration and scan path length. – by Abigail Sutton
Disclosures: Asfaw reported no relevant financial disclosures. Please see the full study for all remaining authors’ financial disclosures.
Perspective
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Carl H. Jacobsen, OD, FAAO
Careful change analysis of baseline structural parameters (neuroretinal rim, nerve fiber laye, and ganglion cell complex) allows for early glaucoma diagnosis. Indeed, structural IOP-related change to these tissues is the definition of glaucoma. Monitoring these parameters for further change allows us to gauge glaucoma progression and adjust treatment accordingly. As glaucoma progresses, the visual field is affected, and structural change takes a back seat to functional analyses. In advanced disease, we are entirely dependent on visual fields as structural changes are no longer identifiable.
What test do your glaucoma patients hate the most? Most of my patients would endure a 20-minute gonioscopy session if they could get out of visual field testing. What tests would you rather interpret? Most clinicians prefer objective, computer-assisted OCT analysis to sitting down with a long series of noisy, subjective bits of visual field data. For this reason, researchers have sought (largely without success) more objective measures of functional vision loss in glaucoma. Asfaw and colleagues suggest we add eye movement analysis to this list.
I’m all for a more objective measure of vision function, and these results are encouraging, but I’m skeptical that eye tracking will become a valued clinical test in glaucoma. In the meantime, it’s good to have another little piece to add to our glaucoma understanding.
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