Contrast sensitivity decline with ageing: a neural or optical phenomenon?

Previous studies of contrast sensitivity changes with age have produced conflicting results. Most recent reports indicate that, with increasing age, contrast sensitivity at medium and high spatial frequencies decreases. Whether this is caused by reduced retinal illumination due to senile pupillary miosis and increased lens absorption, by the greater light scatter of the aged eye or by retinal and neural cell loss and degeneration is also in doubt. We measured the contrast sensitivity functions of 16 young (mean age 21.5 +/- 2.7 years) and 16 older (mean age 72 +/- 4.3 years) subjects with normal healthy eyes, using a modified Rodenstock retinometer and a monitor-based computer system. The former method bypasses the effects of the optical media to measure the contrast sensitivity function of the retinal and neural system alone, while the latter measures the contrast sensitivity function of the whole visual system, including media. The results show the older group to have significantly lower contrast sensitivity at medium (4 c deg-1, p less than 0.1) and high (10.6 c deg-1, p less than 0.001; 16.5 c deg-1, p less than 0.001) spatial frequencies. They also suggest that this is due primarily to retinal and neural changes with age, with optical factors having a slight effect at the highest spatial frequency only.