Prefrontal Cortex Oxygenation Evoked by Convergence Load Under Conflicting Stimulus-to-Accommodation and Stimulus-to-Vergence Eye-Movements Measured by NIRS

Abstract

Purpose: To extend our knowledge of the functional linkages between visual fatigue and regional cerebral prefrontal cortex (PFC) oxygenation, we measured time related hemodynamic changes over the right dorsolateral prefrontal cortex (dlPFC) during convergence load under conflicting stimulus-to-accommodation and stimulus-to-vergence eye movements with and without concurrent mental load.Methods: Twenty healthy participants with a median age of 28 years (range: 18–44 years) fixated upon a vertical bar presented separately to the left and right eyes, using polarized filters, during four counterbalanced 10-min periods: (i) no accommodation/vergence conflict (Control, Ctrl); (ii) added convergence load and accommodation/vergence conflict (Conv); (iii) added cognitive load only (Cog) and; (iv) a combination of added cognitive and convergence load and accommodation/vergence conflict (Cc). Viewing distance was 65 cm. Non-invasive measurements of hemodynamic activity over the dlPFC were quantified by functional near-infrared spectroscopy (fNIRS). During the two-convergence load conditions, the horizontal disparity of the two bars varied dynamically from no disparity to a disparity set 20% below the individual threshold for diplopia. Cognitive load was induced by the n-back-2 test which required the subject to memorize and recall the changing colors of the horizontal bars and decide when a given color was the same as that occurring two colors previously. fNIRS data were averaged over 10-s windows centered at 0, 2, 4, 6, 8, and 10 min of each task, subtracted from a 20-s baseline window immediately preceding the visual task, and then represented as changes in oxygenated hemoglobin (ΔHbO2), deoxygenated hemoglobin (ΔHHb) and total hemoglobin (ΔtHb).Results: Linear mixed model analyses showed that hemodynamic activity was systematically influenced by time (p < 0.001). The group-averaged time-related level of change across the viewing conditions did not differ when compared with one another (p > 0.05). Larger convergence eye-movement responses under conflicting stimulus-to-accommodation, and stimulus-to-vergence over time, increased ΔHbO2 and ΔtHb only in condition Cc and after 8 min of task time (p < 0.10 for min-6 and min-8: p < 0.05 for min-10).Discussion: Collectively, our data suggest that HbO2, HHb, and tHb, recorded over the dlPFC with fNIRS, can be used to assay the degree to which supervisory oculomotor control processes are activated during visually deficient near work.

Decoding visual fatigue in a visual search task selectively manipulated via myopia-correcting lenses

“…Hence, it will be interesting to extend our study to participants with normal vision to test generalizability of our results. In addition, one study using Near-Infrared-Spectroscopy (NIRS) highlighted increased oxygenation in pre-frontal cortex due to visual fatigue (Richter et al, 2018 ). This part of the brain was not implicated in our study, with results focused on other brain networks.…”

“…Despite its ubiquity and impact, the neurological basis of visual fatigue remains poorly understood. The majority of existing studies have mostly concentrated on the effects of physical factors on the ocular system such as excessive accommodation (Sheppard and Wolffsohn, 2018 ), or eye muscle strain (Richter et al, 2018 ). In the context of screen use, for example, researchers have suggested the term “digital eye strain” associated with prolonged and continuous use of computer screens due to both increased accommodation demands on the eye muscles, as well as the occurrence of dry eyes as a result of less blinking (Portello et al, 2012 ).…”

“…Among the few studies using neuroimaging in the context of visual fatigue, Richter et al ( 2018 ) used Near-Infrared-Spectroscopy (NIRS) to show that oxygenation changes localized around pre-frontal cortex went along in response to increased convergence demands and visual fatigue resulting from repeated vergence and accommodation conditions. In Chen et al ( 2017 ), BOLD-fMRI was employed to investigate cortical areas involved in stereopsis and associated visual fatigue from 3D TV.…”

The Effects of a Single Session of a Rhythmic Movement Program on Selected Biopsychological Parameters in PD Patients: A Methodological Approach

“…The distance between NIRS optodes (i.e., sender and receiver) will be 25 mm, enabling a maximum penetration depth of 23 mm and an average measurement depth of 12.5 mm. Increased brain activity is generally considered to mirror increases in local HbO 2 and decreases in HHb, resting on the mechanistic foundation of neurovascular coupling [ 22 ]. Decreased HbO 2 responses can be considered a measure of neuronal suppression or altered hemodynamic re-distribution.…”

Visual ergonomics, performance and the mediating role of eye discomfort: a structural equation modelling approach

“…In that case, they may experience CVS symptoms and difficulty performing their tasks [26]. Employees may also increase their visual effort to achieve the expected level of performance in visually impaired working conditions [27], and this can lead to a feeling of reduced visual performance and an unhealthy experience of stress [26,28]. In addition, if the nature of the work is mentally challenging, the blink rate may decrease [29], which can be a risk factor for ocular symptoms [26].…”