Background: Unlike the usual skeletal muscles, ciliary muscles responsible for focusing the crystalline eye lens and extraocular muscles responsible for convergence eye movements appear resistant to fatigue. Purpose: The dual goals of this article are to briefly outline the current evidence that suggests that probing into blood flow and hemodynamic prefrontal brain activity with Near-Infrared Spectroscopy (fNIRS) could advance progress in visual ergonomic research, and to provide pilot data exemplifying the proposed approach. Methods: The vision task consisted of sustained focusing on a contrast-varying black and white Gabor grating. Four participants with a median age of 46 (IQR 44 – 50) fixated the grating from a distance of 65 cm. Three counterbalanced 10-min tasks required central fixation and accommodation/convergence on the grating target through: (i) 0.0 diopter (D) lenses, (ii) −1.5 D lenses, and (iii) −3.5yD lenses while maintaining maximal focus. Non-invasive measurements of local oxyhemoglobin (HbO₂) were quantified with a one-channel Near Infrared Spectrometer, NIRS. The NIRS probe was placed on the prefrontal cortex in the vicinity of the right dorsolateral prefrontal cortex or Brodmann area 46 (DLPFC, BA 46). Accommodation response and contrast threshold was measured in parallel. Results: General estimating equation analyses showed that baseline subtracted DLPFC blood flow (ΔHbO2) increased significantly over time in all three lens conditions. The effect of time may be caused by a continuous increase in mental effort to compensate for progressively more mental fatigue induced by increased visual attention. The increase of DLPFC ΔHbO2 was also larger in magnitude in participants with larger amplitudes accommodation response (i.e., in participants who minimized deterioration in visual performance). Conclusion: The results from this study indicate that oxyhemoglobin changes recorded over DLPFC with NIRS can be used to assay the degree to which the visual system is strained during demanding near work.