Changes in differential threshold in patients with glaucoma during prolonged perimetry.

Patients with chronic open-angle glaucoma and others suspected of having glaucoma were subjected to continuous contrast threshold measurement by automatic and manual perimetric techniques. The results show that an increase of contrast threshold over time is a frequent finding in glaucoma patients and that this increment can be large, especially at points close to existing field defects. it is reproducible and independent of background illumination and can be demonstrated with both automatic and manual testing, but it is larger in the automatic than in the manual mode of testing. The results may have some important implications for visual field testing in glaucoma.