It has been problematical to decide how much a baby or young child can see; a subject for speculation for many years. In the young, where subjective results are unobtainable or unreliable, a method of objective examination must be used.
Optokinetic nystagmus was observed by Purkinge in 1825 and evaluated by Von Helmholtz in 1867. The eyes of a normal subject fix and follow the movement of an object to the periphery of the field and quickly jerk back to take up fixation on the next object.
It has been found that targets of decreasing size may be presented until they become too small to be fixed and nystagmus is no longer elicited. Use of this phenomenon is made with the present technique.
The apparatus consists of a hand held screen with a central aperture, a drum with targets consisting of a horizontal black line five minutes of arc thick offset by one minute placed around this aperture. The drum is rotated by a motor which oscillates the appropriate target across the aperture with a slow phase and quick return.
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