Eye Movements During Monocular Fixation

Abstract

A METHOD of recording small eye movements during monocular fixation has been described by one of us¹, in which a beam of ultra-violet radiation (λ = 3650 A.) is incident on the cornea in such a direction that the fraction of the light transmitted through the cornea falls on the subject‘s blind spot when some test object is fixated by the illuminated eye ; the subject is then, in effect, only aware of the fixation target. Part of the radiation, however, is reflected at the cornea ; this reflected beam strikes a half-aluminized mirror and is there divided so that one part falls on a vertical straight edge and the other on a horizontal one. In each case, more or less of the radiation passes the straight edge as the eye moves, the fraction passed being focused on to an electron multiplier photocell. The output of each multiplier is amplified and fed to a cathode ray oscillograph, the time base of which is suppressed. The two oscillograph beams are in this way arranged to give vertical traces only, which are photographed simultaneously on a continuously moving film travelling in the horizontal direction. The eye movements can then be deduced from the two records on the film. The system is sufficiently sensitive to detect eye movements of 1 minute of arc ; deflexions due to noise from the multipliers do not, in general, correspond to more than half a minute of arc.