The human eye as an optical filter

The properties of the image-forming elements of the human eye are compared with the properties of the retina-brain system by considering them as two linear optical filters in cascade. The contrast sensitivity of the complete system is measured at a number of spatial frequencies by generating grating patterns of variable contrast and spatial frequency on an oscilloscope. Similar gratings are generated directly on the retina by means of Thomas Young interference, using a neon-helium laser as a coherent light source. In this manner the effect of the eye's dioptrics are bypassed. The quality of the image formed on the retina may then be determined from these two sets of measurements. The effect of pupil size on the quality of the retinal image is described to illustrate an application of the technique.