The functional disturbances of the eyes which I wish to discuss here may be caused either by anomalies of the dioptric or of the motor apparatus or by anomalies the nature of which is not yet known. Though they have been discussed many times, they are not fully understood at present. For instance, it is not known why various subjective disorders, such as eyestrain and headache, may result from comparatively slight degrees of heterophoria or astigmatism, whereas the majority of patients, even those with a high degree of the same anomalies, do not complain of any discomfort. That there is, indeed, a causal connection between the subjective disorders and the anomalies under discussion is evidenced by the frequent disappearance of the symptoms after a proper correction of the anomalies. One of the characteristics is the similarity of the subjective symptoms of which patients with different anomalies complain. Eyestrain,