Contrast sensitivity function (CSF) measures the overall sensitivity of the visual system from the retina to the visual cortex. There are numerous diseases, clinical and physiological conditions as well as aging processes that can influence the CSF.
The 22 subjects (8 male and 14 females) ranging in age from 19 to 75 years that participated in the study were divided into two groups - below and above 50 years of age. The older patients were all pseudophakic. All subjects underwent complete eye examination and were refracted and corrected for the trial's working distance of 1.5 meter. Scotopic CSF was tested monocularly after 3 minutes of dark adaptation by a computerized method using Gabor patches as targets with spatial frequencies between 1.5-6 cycles per degree (cpd). The test was conducted in a completely darkened room, with the monitor covered with neutral density filters having a luminance of 0.35 cd/m2.
The mean CSF for the older age group was 11.6, 10.3, 5.5, 2.9 for 1.5, 2.25, 3, 6 cpd respectively while the mean CSF for the younger age was 20.7, 9.8, 3.8, for the frequencies of 1.5, 3, 6 cpd respectively. Univariant analysis had found the association between CSF and both age group and spatial frequencies to be statistically significant (p=0.027, p<0.001 for age group and spatial frequency, respectively). A fair negative correlation between age and the dark-adapted contrast sensitivity was calculated (correlation coefficient=-0.35, p=0.004, adjusted for spatial frequency).
CSF under nearly scotopic conditions declines with age, a decline that can only partially explained by preneuronal factors. In both age groups the CSF declines with increasing spatial frequency. In most of the older subjects the 6 cpd Gabor patches were too difficult to detect. This selective CSF loss may reflect either reduction in cone spacing, or decreased efficiency of neural processing from the fovea to the cortex. The fact that the younger subjects are sensitive to the higher spatial frequencies and the fact that the test was performed only after 3 minutes of adaptation, support our assumption that we are measuring a foveal function. The simplicity, duration and personal computer compatibility make the procedure practical and readily available for use in clinical settings.