Exploration of brain function changes in the visual cortex of astigmatic subjects based on fNIRS

The primary objective of this research is to explore changes in brain activity among astigmatism patients, employing functional near-infrared spectroscopy (fNIRS). A prospective cross-sectional study comprising 57 participants (99 eyes) was conducted and segmented into three distinct sections. In PART I, 24 participants (48 eyes) with astigmatism (Group A) and 18 participants (36 eyes) without astigmatism (Group B) were assessed using fNIRS to investigate the variations across different brain regions and channels. PART II involved 15 participants with monocular astigmatism (15 eyes), who received complete spherical optical correction, followed by fNIRS assessments after visual stimulation using E-Prime software. The study examined the activation levels of the occipital visual cortex and the functional connectivity strength of the brain, comparing these metrics pre- and post-cylindrical correction. PART III: Following the correction of the initial refractive error in Group A, + 2.00 diopter cylinder (DC) lenses were employed to induce astigmatism at various axes. These axes were categorized into three groups: oblique astigmatism group, with-the-rule astigmatism (WTR), and against-the-rule astigmatism (ATR). fNIRS was conducted during task performance to assess the strength and activation level of brain functional connectivity across different astigmatism axes of the same diopter. PART I: The functional connectivity strength of HbO2-based occipital cortex was stronger in group B than in group A (P 0.05). PART III: The functional connectivity strength and activation level of the HbO2-based occipital visual cortex exhibited significant variations across different astigmatism axes (P < 0.001 and P = 0.045). Specifically, the functional connectivity strength in the oblique astigmatism group was greater than that observed in both the WTR and ATR groups. Conversely, the degree of brain activation in the oblique astigmatism group was lower compared to the ATR group (P = 0.042). These observations imply that astigmatism may decrease both the activation of the occipital visual cortex and the strength of brain functional connectivity. The functional activities of the occipital cortex can be enhanced to a certain degree following optical correction of astigmatism. The strength of functional connectivity and the degree of activation in the occipital visual cortex vary with different axes of astigmatism. Trial Registration This study was registered in the China Clinical Trials Registry (registration number: ChiCTR2300070613, date of registration: 2023-04-18), and the study followed the ethical principles required by the Declaration of Helsinki, and the subjects were informed and signed the informed consent form, and it has been reviewed and approved by the Medical Ethics Committee of the Affiliated Hospital of North Sichuan Medical College (Approval No. 2022ER541-1).