Slowed Saccadic Reaction Times in Seemingly Normal Parts of Glaucomatous Visual Fields

Thepass, Gijs; Thepass, Gijs; Lemij, Hans G.; Vermeer, Koenraad A.; van der Steen, Johannes; van der Steen, Johannes; Pel, Johan J. M. · 2021 · DOAJ

DOI: 10.3389/fmed.2021.679297

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Summary

This study investigates the relationship between visual field sensitivity and visual field responsiveness in patients with glaucoma, aiming to determine if eye movement metrics can detect functional changes before standard sensitivity loss occurs. While Standard Automated Perimetry (SAP) is the gold standard for assessing visual field sensitivity, it has limitations regarding reliability and early detection. The authors hypothesized that Saccadic Reaction Time (SRT), measured via Eye Movement Perimetry (EMP), would increase with decreasing sensitivity and that SRTs would be elevated even in visual field locations deemed normal by SAP in glaucomatous eyes. The study included 34 healthy controls and 42 glaucoma patients (stratified into mild, moderate, and advanced groups based on Mean Deviation). Participants underwent both a 24-2 SITA SAP protocol and a 54-point EMP protocol using an eye-tracking system. In the EMP test, subjects fixated on a central target and made saccades toward peripheral stimuli. SRT was defined as the time between stimulus presentation and saccade onset. Data were analyzed using a generalized linear mixed model to assess the influence of glaucoma severity, stimulus intensity, eccentricity, and SAP sensitivity loss on SRT. Visual field locations were categorized into six bins based on total deviation sensitivity loss. Results demonstrated that mean SRT increased significantly with glaucoma severity, rising from 479 ms in controls to 678 ms in advanced glaucoma. Crucially, SRTs were significantly lengthened in glaucoma patients compared to controls even at locations with no detectable sensitivity loss on SAP (total deviation ≥ 0 dB). This effect was present across mild, moderate, and advanced glaucoma groups. SRT also increased with greater sensitivity loss, dimmer stimuli, and larger stimulus eccentricity. Age, gender, and eye laterality did not significantly correlate with SRT. The findings indicate that slowed saccadic reaction times precede altered sensory perception as measured by standard perimetry. This suggests that motor responses, specifically the planning and execution of saccades, are affected by glaucomatous damage before functional sensitivity loss is detectable. The authors conclude that EMP and SRT measurement may offer a more sensitive tool for the earlier diagnosis of emerging glaucoma, potentially identifying pre-perimetric functional changes that correlate with the known loss of retinal ganglion cells prior to visible visual field defects.

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• sensory abilities