Functional near-infrared spectroscopy has yet to be implemented as a stand-alone technique within an ophthalmology clinical setting, despite its promising advantages. The present study aims to further investigate reliability of visual cortical signals. This was achieved by: (1) assessing the effects of optode placements using the 10–20 International System of Electrode Placement consisting of 28 channels, (2) determining effects of stimulus size on response, and (3) evaluating response variability as a result of cap placement across three sessions. Ten participants with mean age 23.8 4.8 years (five male) and varying types of hair color and thickness were recruited. Visual stimuli of black-and-white checkerboards, reversing at a frequency of 7.5 Hz were presented. Visual angles of individual checker squares included 1 deg, 2 deg, 5 deg, 9 deg, and 18 deg. The number of channels that showed response was analyzed for each participant, stimulus size, and session. 1-deg stimulus showed the greatest activation. One of three data collection sessions for each participant gave different results (p < 0.05). Hair color and thickness each had an effect upon the overall HbO (p < 0.05), while only color had a significant effect for HbD (p < 0.05). A reliable level of robustness and consistency is still required for clinical implementation and assessment of visual dysfunction.
Nasser H. Kashou and Brenna M. Glacherio, "Stimulus and Optode Placement Effects on Functional Near-Infrared Spectroscopy of Visual Cortex," Neurophotonics, 3 (2) 025005, (2016).