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Retina
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# 199 - Eye, rabbit, sagittal section through entire eye, h-e # 202 - Cornea, monkey, section, h-e |
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The first retinal layer is composed of 1) pigmented epithelium resting on a basal lamina (Bruch's membrane) adjacent to the choroid. The next three layers are composed of various portions of one cell type, the first neuron. These layers are the 2) region (lamina) of rods and cones, 3) the external limiting membrane, and the 4) outer nuclear layer (composed of the nuclei of the rods and cones cells). The rods have long, thin bodies, and the cones have a broad base. The former has greater sensitivity for low light levels; the latter has better visual acuity in daylight and are also responsible for the perception of color. Like the sensory epithelium found in the nose and ear, the rod and cone cells are supported by sustentacular (glial) cells called Muller's cells whose nuclei are found in the inner nuclear area and whose cytoplasm extends from the inner limiting membrane to the external limiting membrane. The latter can be seen with light microscopy; with EM, it was seen to be a region of terminal bars between Muller's cells and the visual receptors. The next three layers of the retina are composed of various parts of the second neurons whose nuclei reside in the 6) inner nuclear layer and whose cytoplasmic processes extend into the 5) outer plexiform layer to synapse with the receptor cells and to the 7) inner plexiform layer to synapse with the ganglion cells. Thus, the second neuron is bipolar. The third neuron, the multipolar 8) ganglion cell sends its 9) nerve fiber (axon) to the optic nerve. The last layer of the retina is the 10) internal limiting membrane on which rests the processes of Muller's cells. The human retina can be divided into a central area of a 5 - 6 mm diameter and a peripheral area. There is an accumulation of ganglion cells in the central area. The macula lutea ("yellow spot") is an area of rods which surrounds the shallow pit of the fovea centralis. In the fovea some inner layers of the retina are absent. The cones are the only visual cells present in the fovea and it is the region of keenest vision. |
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Retina Layers (unlabeled) |
Retina Layers (labeled) |
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Red single headed arrow - Pigmented Epithelium Blue double headed arrow - Area of Rods and Cones Green singel headed arrow - Internal Limiting Membrane black arrows - Outer Nuclear Layer Red double headed arrow - Outer Plexiform Layer Yellow double headed arrow - Inner Nuclear Pink arrows - Inner Plexiform Layer Blue singe headed arrrow - Ganglion Cell Layer double headed green arrows - Optic Nerve Layer
This is an image of where the Optice Nerve leaves the eyeball, indicated by the blue arrows. As you can see the layers of the retina are lost where the optic nerve exits the eye. This causes a physiological Blind spot because there are no photoreceptors in that part of the retina. Blue arrow - Optice Nerve Exiting Eye ball |
These are two images of the Layers of the Retina. One is put with out labels to look at with out the clutter of all the labels. The retina has 10 histologically Identifiable Layers. Starting from the outermost layer first, the First layer is the Pigmented epithelium, single head red arrow. The second layer is the Region of the Rods and Cones (blue double headed arrows) which is where the photoreceptors are found. The next layer is the External Limiting Membrane (green single head arrow) which is a fine thin line. The fourth layer is the Outer Nuclear layer, (black arrows) which is where the photoreceptor's nuclei are located. The fifth layer is the Outer Plexiform layer (red double headed arrows) which is where the photoreceptors synapse with the Bipolar cells. The sixth layer is the Inner Nuclear Layer (yellow arrow) which is where the Nuclei of the Bipolar cells are. The seventh layer is the Inner Plexiform Layer (pink arrows) which is where the Bipolar Cells synapse with the Ganglion Cells. The eigth layer is the Ganglion Cell Layer, (blue singel headed arrow) which is the location of the nuclei of the ganglion cells. The ninth layer is the Optic Nerve layer, (green double headed arrow) which is where the axons of the ganglion cells coalesce to form the Optic Nerve. The tenth and inner-most layer is the Internal Limiting membrane.
Optic Nerve |
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This is an image showing the Ora Serrata (blue arrow). This is the depression seen in the image. Anterior to the ora serrata there is no Retina, which is the area indicated by the red arrow. Posterior to the ora serrata is the Retina. Blue arrow - Ora Serrata Red arrow - No Retina Area |
Ora Serrata |
