The authors analysed the cases of 13 patients, operated upon for chronic glaucoma with marked visual-field defects. The visual field was examined with a Zeiss spherical perimeter. The field area was calculated in cm2 by planimetric method before the operation and then some months after it, and the obtained results were compared. Special attention was paid to vascular disturbances. In most patients with regular vascular system, post-operative examination had revealed an increase of the visual field. The best results were obtained in patients with medium-size defects: in these cases the increase in the visual field amounted to ca. 33%. The authors recommended proceeding to operative treatment in glaucoma patients without delay whenever there are defects in the visual field, even when they are very pronounced.