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A system has been devised for causing an image to remain at one point on the retina regardless of eye movements. A beam of light, reflected from a plane mirror on a contact lens, is used to project onto a screen an image of a dark line against a bright background. The screen is viewed by the same eye through an optical system which compensates for the doubling of the angle of rotation of the beam projected from the mirror on the contact lens. Thus, any motion of the eye causes a deviation of the beam such that the retinal image of the projected line undergoes the same displacement as do the retinal receptor cells. By comparison with normal viewing of the same test objects it is found that (1) when first presented, the finest lines are seen with normal or slightly better than normal acuity, (2) within a few seconds the lines begin to disappear, and (3) within one minute even coarse lines are seen only intermittently. The results may be interpreted in terms of local retinal adaptation to a stationary field.

Eye movements during monocular fixation were photographically recorded using the contact lens mirror technique. Records were taken during normal viewing and during viewing with a stabilized retinal image. Flicker was used to produce various durations of disappearance of the fixated figure under both conditions. Characteristics of the drifts and saccadic components of the eye movements were compared under these conditions. It was found that, (1) the rate of drift is the same for all conditions, (2) there are many fewer saccades during stabilized than during normal viewing, and (3) the frequency of saccades is independent of the duration of disappearance for stabilized viewing. An analysis of the characteristics of saccadic movements showed that their probability of occurrence, direction, and magnitude are dependent upon the position of the retinal image on the retina. No comparable relationship was evident for the drifts of the eye. Eye movement records taken in the dark indicate that, in the absence of visual control, the eyes are incapable of maintaining their fixation. Proprioceptive feedback, therefore, does not appear to play an important part in the fine corrective movements that serve to maintain ordinary fixation. It is concluded that the primary stimulus condition for involuntary saccadic eye movements is displacement of the retinal image on the retina, and that drift is the result of an instability of the oculomotor system.

No abstract