The mechanics of human saccadic eye movement

Abstract

In the investigation of oculomotor systems and especially in the mathematical descriptions of them as pursuit, tracking and stabilizing systems, the need arises for a more exact knowledge of the mechanics of the eyeball, the extraocular muscles and the supporting tissues of the orbit, particularly of the way in which these factors permit the globe to respond to the efferent discharges arising in the oculomotor nuclei. In 1954 Westheimer proposed that the eye moved in a saccade by the application of a step function of net muscular force. He further proposed that the mechanical system was of second order, slightly underdamped and had a natural resonant frequency of about 120 radians per second (19 c/s). Alpern (1962) has discussed the inadequacy of this picture in view of the large burst of activity during a saccade recorded by extraocular electromyography (Bj6rk, 1955; Miller, 1958).The development of the suction contact lens has made practicable a closer investigation of the mechanics of the saccade, for it provides a simple method of applying known forces and loads to the eye while measuring subsequent rotations without fear of lens slippage. The evidence presented here will demonstrate that the system of eyeball and orbital tissues is heavily overdamped, has no resonant frequency and is little affected by the mass of the eyeball. It has an upper mechanical frequency response of only 1 c/s and it succeeds in making quick saccadic movements only under the impetus of a large, briefly applied, excess force delivered by the extraocular muscles. For example, in maintaining the eye 100 horizontally from the primary position the horizontal recti need apply a net force of only 15 g but during the saccade to reach that position they apply about 43 g during the first 40 msec of movement. METHODSThe experiments involved four procedures with the intact human eye and one with the lateral rectus of the cat. Three human, normal, adult, male subjects were used. The human experiments were conducted with normal room lighting illuminating a horizontal row of black dots spaced 50 apart on a white spherical background 1 m from the subject.

The cat's vestibulo‐ocular reflex.

“…In Carpenter's experiments, it appeared that the high-frequency asymptote of the v.o.r. was being determined by the viscous forces in the orbital mechanics; these possess a corner frequency of 1 1 Hz (Robinson, 1964). There is no obvious explanation for this effect of decerebration on the v.o.r.…”

“…Robinson (1964) has shown that the viscous elements in the orbit begin to impose phase lag into the eye's force-movement relationship in the same frequency range, 0*5-1*0 Hz, as that in which canal neurones display phase lead. If the brain stem path of the v.o.r.…”

“…At frequencies greater than 1 Hz the viscous elements in the orbital tissues effectively introduce an integration into the force-movement relationship between the extra-ocular musculature and the globe (Robinson, 1964). At such frequencies the v.o.r.…”

System Identification From Multiple Short-Time-Duration Signals

“…The connective tissue of the oculomotor plant is a viscoelastic structure [18], which can be represented by a small number of Voigt elements in series [6], [7], as described in Fig. 4.…”

Eye Movement Research in the Twenty-First Century—a Window to the Brain, Mind, and More

“…Conceptually, bioengineering approaches, using systems analytical techniques, were combined with anatomical and physiological data, to develop biologically plausible models, replacing the Bblack box^approach to neural modeling. The involvement of bioengineers in eye movement research, exemplified by David A Robinson, enticed basic and clinical neuroscientists to adopt the Bengineering approach^to understanding normal brain function and human disease [27,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47].…”