This study investigated the daily trends in the spatial and temporal heterogeneity of cone photoreceptor reflectivity. Cones contain a high density of mitochondria in their inner segments, and metabolic rates are thought to vary on a daily cycle. To test this, both eyes from ten healthy human volunteers were imaged multiple times per day (9:00am, 11:00am, 1:00pm) with an adaptive optics flood illumination camera before and after stimulation of one eye with a uniform red light, the wavelength of which is thought to promote mitochondrial metabolism. Results indicate strong statistical relationships between time of day and cone reflectivity and spatial heterogeneity. Irrespective of red light stimulus, cone reflectivity decreased by an average of 3.08 ± 3.22% in the afternoon compared to morning, and spatial heterogeneity decreased by 6.43 ± 4.51%.
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