We have investigated the effect of ageing on the visual system using the relatively new technique of magentoencephalography (MEG). This technique measures the magnetic signals produced by the visual system using a SQUID magnetometer. The magnetic visual evoked field (VEF) was measured over the occipital cortex to pattern and flash stimuli in 86 normal subjects aged 15 - 86 years. Factors that influenced subject defocussing or defixating the stimulus or selective attention were controlled as far as possible. The latency of the major positive component to the pattern reversal stimulus (P100M) increased with age particularly after the age of 55 years while the amplitude of the P100M decreased over the life span. The latency of the major flash component (P2M) increased much more slowly with age, while its amplitude decreased in only a proportion of elderly subjects. Changes in the P100M with age may reflect senile changes in the eye and optic nerve, e.g. senile miosis or degenerative changes in the retina. The P2M may be more susceptible to senile changes in the retina. The data suggest that the spatial frequency channels deteriorate more rapidly with age than the luminance channels and that MEG may be an effective method of studying ageing in the visual system.
|Publication status||In preparation - 1990|
|Event||Society of Experimental Optometry - |
Duration: 1 Jan 1990 → 1 Jan 1990
|Conference||Society of Experimental Optometry|
|Period||1/01/90 → 1/01/90|
Bibliographical noteAbstract appearing in Papers presented at the meeting of The Society for Experimental Optometry, at Birmingham on 23–24 July 1990, Ophthalmic and Physiological Optics, (October, 1990), 10 (4), p.414, 0275-5408.
- visual system
- magnetic signals
- SQUID magnetometer