Diurnal variation of visual field size in patients with postretinal lesions.

Perimetry at various times of day in patients with large visual field defects due to postretinal lesions showed significant variations of visual field size. The largest visual fields were observed at noon, the smallest in the evening. Such systematic variations were observed only in patients who showed a gradual increase of increment threshold between the intact parts of the visual field and the scotoma. In two patients who showed an abrupt transition between intact and blind areas of the visual field, no obvious diurnal variation was observed. It is suggested that an endogenous modulation of neuronal sensitivity coupled to a hypothetical circadian oscillator is the basis of the diurnal variation.