Nonlinear Servoanalysis of Human Lens Accommodation

Abstract

The automatic focusing system of the human eye is an important biological and neurological servomechanism and has attracted the interest of many physiologists, experimental psychologists, and optometrists. When a man looks at an object his eyes focus on the target and the result is a clear image on the retina. When the eye does not focus on the object the retinal image blurs. The information concerning the state of the retinal image is sent to the central nervous system which processes it and relays to the ciliary muscle orders either to contract or to relax and thus to change the refractive power of the lens. This feedback loop is represented by the block diagram of Fig. 2. The way that the central nervous system processes the information sent from the retina is still unknown, although several hypotheses have been put forward, relating to the effects of aberrations and noise [13, 19, 38, 39].