Masters of Health Magazine September 2018 - Page 20

Fig 1. Anatomy of the inverted mammalian retina

The primary source of retinal dopamine is found in the amacrine cells (see Fig 1); their cell bodies in the inner nuclear layer of the retina that synapse directly with ipRGCs found in the inner-most ganglion cell layer of the retina.

The mammalian retina is referred to as an “inverted” retina. Light, after entering the eye through the pupil and passing through the lens and vitreous, is normally focused on the retina at the posterior pole forming an image of the object of regard.

The retinal architecture is arranged with specialized light sensitive visual cells, the rods and cones, within the outer retinal layers. Light must pass through the transparent retinal layers before reaching these cells deepest within the retinal anatomy but anatomically located ‘behind’ the all-important ganglion cell layer (that contains ipRGC’s) relative to the pathway of light forming the retinal image.

The summary by Zhou published in 2015 that reviewed the research on the mechanism behind retinal dopamine and its effect on eye growth provides a useful model of the inter-action of the dual systems of retinal dopamine receptors, respectively D1 and D2 .

The model proposed outlined the close inter-action between the D1 and D2 receptors that when appropriately balanced results in emmetropia (see Fig 2).

Neuro-anatomy of the retinal dopamine pathway