The visibility of retinal blood vessels.
D000328:Adult; D000368:Aged; D005403:Fixation, Ocular; D006801:Humans; D008027:Light; D008297:Male; D009068:Movement; D010783:Photometry; D012171:Retinal Vessels / Q000033:anatomy & histology; D013997:Time Factors; D014785:Vision, Ocular