Abstract
A description is given of the components of the human eye as an image-forming system, and of a model eye based on Gaussian optics. The actual performance of the eye's optics is discussed with respect to chromatic aberration, absorption losses, scatter and the in vivomeasurement of the modulation transfer function. Physiological aspects of the eye's visual performance are described, including pupil size, and the influence of various factors on visual acuity.