Fig 3. Approach used to automatically measure the caliber of a selected retinal vein.

(a) View of the tree shrew optic nerve head, with a line segment crossing the selected vein. (b) Green channel intensity was plotted for the selected pixels on this line segment; vein caliber was taken as the full-width-at-half-maximum of the intensity plot. (c) The resulting vein caliber measurement (overlaid) corresponded well to the expected vein caliber.