Flatmount view of a rat retina stained with NADPH-diaphorase at the level of focus of (more.) Flatmount view of a rat retina stained with NADPH-diaphorase at the level of focus of a major artery and arterioles. The greater number of ganglion cells means more synaptic interaction in a thicker IPL and greater numbers of ganglion cell axons coursing to the optic nerve in the nerve fibre layer ( Fig. This is again due to the greater numbers and increased packing-density of ganglion cells needed for the cone pathways in the cone-dominant foveal retina as compared the rod-dominant peripheral retina. As we shall see later, cone-connected circuits of neurons are less convergent in that fewer cones impinge on second order neurons, than rods do in rod-connected pathways.Ī remarkable difference between central and peripheral retina can be seen in the relative thicknesses of the inner plexiform layers (IPL), ganglion cell layers (GCL) and nerve fibre layers (NFL) ( Figs. The inner nuclear layer (INL) is thicker in the central area of the retina compared with peripheral retina, due to a greater density of cone-connecting second-order neurons (cone bipolar cells), smaller-field and more closely-spaced horizontal cells, and amacrine cells concerned with the cone pathways ( Fig. The latter layer is absent in peripheral retina. These oblique axons, with accompanying Müller cell processes, form a pale-staining fibrous-looking area known as the Henle fibre layer. In central retina, the cones have oblique axons displacing their cell bodies from their synaptic pedicles in the outer plexiform layer (OPL). However in the peripheral retina the rod cell bodies outnumber the cone cell bodies while the reverse is true for central retina. The outer nuclear layer (ONL), composed of the cell bodies of the rods and cones, is about the same thickness in central and peripheral retina. Thus in central retina the cones are closely spaced and the rods fewer in number between the cones ( Figs. The inner nuclear and ganglion cell layers (INL, GCL) contain more cells, (more.)Ĭentral retina is cone-dominated retina whereas peripheral retina is rod-dominated. In central retina the inner and outer plexiform layers (IPL, OPL) are thicker than in peripheral retina. Different structure of central and peripheral human retina. The retinal message concerning the photic input and some preliminary organization of the visual image into several forms of sensation are transmitted to the brain from the spiking discharge pattern of the ganglion cells.įigure 10. Subsequently the absorbtion of photons by the visual pigment of the photoreceptors is translated into first a biochemical message and then an electrical message that can stimulate all the succeeding neurons of the retina. Light must, therefore, travel through the thickness of the retina before striking and activating the rods and cones ( Fig. A radial section of a portion of the retina reveals that the ganglion cells (the output neurons of the retina) lie innermost in the retina closest to the lens and front of the eye, and the photosensors (the rods and cones) lie outermost in the retina against the pigment epithelium and choroid. The optic nerve contains the ganglion cell axons running to the brain and, additionally, incoming blood vessels that open into the retina to vascularize the retinal layers and neurons ( Fig. The retina is approximately 0.5 mm thick and lines the back of the eye. The total retina is a circular disc of between 30 and 40 mm diameter ( 1-3). An animation from the iris to the retina.Ī circular field of approximately 6 mm around the fovea is considered the central retina while beyond this is peripheral retina stretching to the ora serrata, 21 mm from the center of the retina (fovea).
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