Patients with senile macular degeneration (SMD) often complain of problems with adaptation and have best acuity under a restricted range of lighting conditions. We investigated dark adaptation and acuity over a wide range of luminances in eight SMD patients and six age-matched controls. Some patients showed evidence of altered dark adaptation, with a much longer time required to reach asymptotic sensitivity levels than shown by normals; others had difficulty with spatial resolution at different light levels. There was good correlation between symptoms and test findings; all but one patient who reported difficulties with adaptation demonstrated either retarded adaptation, aberrant acuity/luminance response, or both. These data provide evidence that the processes which adjust the sensitivity of the retina and the spatial summation properties of the retina are disrupted in SMD.