Changes in visual cortical function in moderately myopic patients: a functional near-infrared spectroscopy study.

PURPOSE: To investigate haemoglobin oxygenation in the visual cortex of myopic patients using functional near-infrared spectroscopy (fNIRS). METHODS: The experiment consisted of two parts. Part 1 examined functional changes in the visual cortex before and after refractive correction in myopic patients. Subjects were divided into normal controls, uncorrected and corrected myopes. Part 2 examined functional changes in the visual cortex caused by lens-induced myopia in normal subjects, and whether this activity recovered after a period of rest. Here, subjects were divided into three groups: emmetropes, lens-induced myopia and a rest group. The rest group completed a test with the uncorrected eye following lens removal and 5 min of rest. The visual stimulus was a black and white checkerboard. fNIRS was used to detect changes in oxyhaemoglobin content within the visual cortex. The original fNIRS data were analysed using MATLAB to obtain the ß values (the visual cortical activity response caused by the task); these were used to calculate Δß, which represents the degree of change in oxygenated haemoglobin caused by visual stimulation. RESULTS: The Δß value measured in each single channel or only in the region of interest (ROI) was significantly higher in the emmetropic control group than the uncorrected myopic group. After optical correction, the responses of myopic subjects approached those of the emmetropes and were not significantly different. If myopia was induced in emmetropic subjects by imposing defocus with positive lenses, a decline in functional activity was observed similar that observed in uncorrected myopes. Activity recovered after the lenses were removed. CONCLUSIONS: Myopic defocus reduced the level of haemoglobin oxygenation in the visual cortex, but activity could be restored by optical correction.