Dopamine is well accepted as a major neurotransmitter associated with light adaptive processes in the retina and possibly the control of eye growth. Very little is known about dopamine’s precise release patterns in vivo, which is largely due to the lack of an unambiguous method for the determination of dopamine release. This thesis sets out to assess retinal dopamine release in vivo, on the basis of vitreal levels of the dopamine metabolite DOPAC. This method is validated, then used to study diurnal dopamine release patterns and the effects of form-deprivation on release.

Dopamine release, as determined by the vitreal level of DOPAC, increased during the day and decreased at night. With constant darkness, there was a slight circadian drive apparent at the beginning of the subjective day, but this was negligible compared to the light-induced increase in dopamine release. This circadian component was found to be partially due to a circadian decline of melatonergic inhibitory input. Dopamine release was initiated at very low light intensities, coinciding with retinal adaptation to light. Dopamine release increased linearly with the log of light intensity over approximately 4 log units. Deprivation of form-vision was found to have no effect on the initial rise of dopamine release at the transition from dark to light, but suppressed release at later periods during the day. Over longer-term form-deprivation, dopamine release continued to cycle, albeit at lower overall levels.

These release patterns suggests that dopamine functions to signal day/night, the transition from light to dark, ambient lighting status, and possibly temporal and spatial components in the visual image. Dopamine thus optimises the retina’s information processing characteristics to ambient conditions.