Abstract: A diagnostic test for glaucoma, which can detect the early stages of this disease, uses a pattern electroretinogram of a subject to assess any reduction of the density of M.sub.y ganglion cells in a part of the subject's retina. The visual field of the eye of the subject is divided into a number of zones, and a respective visual stimulus signal is applied to each zone. The visual stimulus signals are generated in accordance with data obtained from determinations of the critical spatial frequency (Nyquist frequency) of persons with normal vision, obtained from observations of the "aliasing" phenomenon. Typical visual stimulus signals are grating patterns, with the contrast of the signal applied to each zone modulated with a different temporal frequency in the range of from 10 Hz to 45 Hz. Any differences between the electroretinogram response component for an individual zone and the expected response component for that zone indicates a change in the M.sub.

Abstract: Optokinetic nystagmus is the rhythmical scanning of the eyes when primates attempt to stabilize constantly moving visual scenes. If a pattern having distinct vertical features is projected onto a screen and is drifted to the left or to the right, variations of certain parameters associated with optokinetic nystagmus of a subject observing the drifting pattern from the values of those parameters for persons having normal, healthy vision provide an indication of damage to M-type ganglion cells due to the presence of glaucoma in the subject. Such variations occur at an early stage of glaucoma, before other positive indications of the disease are present. Preferably the projected pattern is a coarse sinusoidal grating with vertical striations, which is temporally modulated by a rapid movement or flicker.

Abstract: Existing techniques for diagnosis of glaucoma, namely observation of a scotoma, measurement of intraocular tension and assessment of color vision defects have drawbacks. The present invention overcomes those drawbacks by a psychophysical test in which a sinusoidal grating pattern is presented to a subject with the contrast of the pattern modulated at a frequency in the range from about 10 Hz to about 50 Hz, so that the subject can observe a frequency-doubled pattern of the grating. The contrast of the pattern is then reduced until a threshold value is reached, at which value the frequency-doubled pattern is no longer observed. The threshold value is then compared with the threshold value for persons of normal vision. A higher than normal threshold value indicates that the subject may be suffering from glaucoma. Persons with well-developed glaucoma have threshold values that are approximately twice the threshold value of a person with healthy vision.