The retina consists of stratified nervous tissue and a single layer of pigment epithelial tissue. The nerve layer is called the sensory retina.
Retinal layers from outside to inside
1. Retinal pigment epithelium: It is a single layer of pigmented cells that are distinguished by their polygonal shape, tight intercellular connections, and apical microvilli that enter between photoreceptors. It has very important functions such as continuous renewal of photoreceptor outer segments and metabolic exchange between photoreceptor cell and choriocapillaris.
2. Photoreceptor cell layer: It consists of approximately 100 million rods and 6 million cones. The photoreceptor cell layer in the 0.4 mm area in the center of the fovea consists only of cones. As the cone concentration decreases towards the periphery, the rod concentration increases.
3. Outer limiting membrane (ELM): It is a membrane appearance formed by the connections between the photoreceptor inner segments.
4. Outer nuclear layer (ONL): It is the layer where the nuclei of the photoreceptor cells are located.
5. Outer plexiform layer (OPL): It is the synapse layer of bipolar cells with photoreceptor terminals.
6. Inner nuclear layer (INL): It is the layer where the nuclei of bipolar, amacrine, horizontal and Müller cells are located.
7. Inner plexiform layer (IPL): It is the synaptic layer between bipolar or amacrine cells and ganglion cells.
8. Ganglion cell layer (GCL): There are 6-8 layers of ganglion cells in the macula, but it goes down to a single layer in the perifovea.
9. Nerve fiber layer (NFL): It is formed by the axons of the ganglion cells.
10. Inner limiting membrane (ILM): It is a membrane formed jointly by the surface modification of the vitreous and the last protrusions of Müller cells.
Of these retinal layers, only the inner limiting membrane, outer plexiform layer, and photoreceptor cells are present in the fovea. Therefore, the middle of the fovea is the thinnest part of the retina.
The fovea contains only cone cells (Enables sharp vision in bright light).
There are also more bacillus cells in the periphery (enables vision in the dark).