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BASIC CONCEPTS RELATING THE EYE AND RETINA.

 

 

The retina from outer to inner side has 8 layers.

 

1.   The pigmented epithelium over which lie the choroidal capillaries which in turn are supplied by major choroidal vessels.

2.   The rod and cone layer collectively called the photoreceptors on which light hits after crossing the inner layers of retina. It has an outer limiting membrane, indicated by the green line in diagram, across the dendrites of the rod and cone cells, and an outer nucleur layer, indicated by the red line that connects the cell bodies of the rod and cone cells.

3.   The outer plexiform layer, indicated by the green bracket. It includes the synapsing junctions between the rod and cone cell layer and the bipolar cells. It is named plexiform because the axons synapse with the dendrites to form a network. THE ABOVE 3 LAYERS ARE PROVIDED NUTRITION BY SIMPLE DIFFUSION FROM THE CHORIO CAPILLARIES.

4.   The bipolar cell layer that contains an inner nuclear layer, across is cell bodies indicated by the black line.

5.   The inner plexiform layer at the synapse between bipolar cells and ganglion cells, indicated by the red bracket.

6.   The ganglion cell layer.

7.   The optic nerve fiber layer.

8.   The inner limiting membrane indicated by the blue line. THE ABOVE 5 LAYERS ARE PROVIDED DIRECTLY BY THE RETINAL ARTERIES.

 

 

The diagram also shows inhibititory gabaergic horizontal cells and amacrine cells. The horizontal cells connect adjacents synapses between rod/cone cells and bipolar cells, while the latter connect adjacent axons and dendrites of ganglion cells and rod/cone cells. In addition to this oligodendrocytes give axonal extensions to the optic nerve fibers and myelinate them while radial (molar) glial cells are large cells that extend from the outer limiting membrane to the inner limiting membrane.

 

The diagram shows rod receptor on the left and cone receptor on the right. The many folds on their membranes are so that they can absorb maximum light. They contain different pigments due to which rods are sensitive to dim light (roDim) or rhodopic vision while cones are sensitive to bright light or photopic vision.

 

THE RODS, CONES, BIPOLAR AND GANGLIONIC CELLS ARE ALL GLUTAMINERGIC.