What is a Fovea?

Foveal is the most sensitive area of vision (color discrimination, resolution) in the retina. Take humans as an example, there is a yellow cell, called the macula, at about 3.5 mm in the temporal side of the optic nerve disk. The central depression is the fovea.

Foveal is the most sensitive area of vision (color discrimination, resolution) in the retina. Take humans as an example, there is a yellow cell, called the macula, at about 3.5 mm in the temporal side of the optic nerve disk. The central depression is the fovea.

Chinese scientific name

Foveal

Latin scientific name

fovea centralis

boundary

animal world

Species

Foveal

Foveal anatomy:

1, the fovea:

The central depression of the macula is called the fovea, where the retina is the thinnest. There are only two layers of pigment epithelial cells and cone cells. The bipolar cells and ganglion cells are arranged obliquely around the periphery. Here the cone cells and the bipolar cells are one-to-one connected, so the vision is the most acute and precise, called central vision.

2. Retina:

The innermost two layers of the three-layer membrane (fibrous membrane, vascular membrane, and retina) of the eyeball wall. Located on the inside of the vascular membrane. It can be divided into three parts: iris part, ciliary body part and visual part. The iris and the ciliary body are attached to the inner surface of the iris and the ciliary body without photosensitivity. The visual part of the retina is attached to the inner surface of the choroid. It is mainly composed of visual cells that can feel light stimulation. The nerve impulses transformed by light stimulation are transmitted to the brain along the optic nerve to form vision.

The retina is the inner layer of the eyeball wall, and is divided into a blind retina and a visual part. The blind part includes the retinal iris part and the retinal ciliary body part, each of which is attached to the inner surface of the iris and the ciliary body and is a component part of the iris and the ciliary body. The retinal vision is often referred to as the retina, which is a soft and transparent film that is closely attached to the inner surface of the choroid and has the effect of feeling light stimulation. The thickness of the retina varies, usually 0.4mm, the edge of the optic disc is the thickest, about 0.5mm, and the fovea is the thinnest, which is 0.1mm, and the jagged edge is 0.15mm. The retina is mainly composed of pigment epithelial cells, optic cells, bipolar cells, ganglion cells, horizontal cells, amacrine cells, reticulum cells, and Muller cells. These cells and their processes are arranged in an orderly manner, so that the retina can be divided into 10 layers from the outside to the inside. Pigment epithelium: consists of a single layer of pigment epithelial cells; rod cone: consists of rod cells and cones' exocytosis; outer membrane: formed by the extruded ends of Muller cells; Nuclear layer: composed of cell bodies of rod cells and cone cells; outer reticulum layer: composed of inner processes of rod cells and cone cells and dendrites of bipolar cells; inner core layer: composed of bipolar cells, Cell bodies of horizontal cells, amacrine cells and Muller cells; Intrasacral reticulum: composed of axons of bipolar cells and dendrites of amacrine and ganglion cells; sacral cell layer: composed of somatic cells The sacral nerve fiber layer: consists of axons of ganglion cells; the sacral limiting membrane: formed by connecting the end of Muller cells.

3. Bipolar cells:

Bipolar cells are the connective neurons of the retina. There are three types of dwarf bipolar cells, flat bipolar cells and rod-shaped bipolar cells. Their morphological characteristics and the connection between synoptic and nodal cells are shown in Figure 2. It should be noted that: only the synapses formed by flat bipolar cells and cone cells are excitatory synapses; the triple synaptic complexes formed by the other two bipolar cells and cone cells or rod cells are inhibitory Synapses; in the fovea of the retina, dwarf bipolar cells only connect one cone cell and one dwarf ganglion cell, forming a one-to-one visual conduction pathway, so the vision is particularly sharp and precise; around the retina, a dwarf bipolar Cells can be associated with 2 cone cells, and a flat bipolar cell can be associated with 6 to 7 cone cells. Conversely, one cone cell can be associated with one or more flat bipolar cells. Rod-shaped bipolar cells can be associated with 2 to 6 rod cells. Bipolar cells transmit information about cones and rods to nodal cells.

Foci with two layers of cells:

1. Pigment epithelium:

It is a layer of short hexagonal prismatic cells, with a height of 8-10 m and a width of 12-18 m. Many 5-7 m long protrusions protrude from the top of the cell. During embryogenesis, the base of the epithelium and the choroid are tightly connected, but the top is not tightly connected with the optic cells, so retinal detachment is prone to occur here. Observed by electron microscope, there are tight junctions, intermediate junctions and gap junctions between the cells, and there are inner membrane folds and mitochondria at the base, so it is speculated that the pigment epithelium has transporting ions and barrier functions. The nucleus is round and located at the base of the cell. The top cytoplasm contains many oval or round melanin particles and lamellar debris. The endoplasmic reticulum of the slippery surface is well developed and is distributed between pigment particles and remnants. There are Golgi complexes, lysosomes, rough endoplasmic reticulum and lipid droplets. These structures reflect the multiple functions of pigment epithelium: pigment particles are produced by the rough endoplasmic reticulum and transported to the top of the cytoplasm via the Golgi complex. It is known that when amphibians and fish are exposed to strong light, the pigment particles move into the protrusions; when it is dark, the pigment particles return to the cytoplasm, which indicates that the pigment epithelium has the effect of absorbing light and protecting the visual cells from strong light. Lipid droplets can accumulate and store vitamin A, and participate in the synthesis of rhodopsin by optic cells through the esterification and transport of the endoplasmic reticulum of the slippery surface; can engulf the outer membrane discs of rod cells and lysosomes Enzymatic hydrolysis digestion and formation of residues; secretion of proteoglycans, binding and maintaining the positional relationship between rod, cone and pigment epithelium, thereby ensuring the renewal of rhodopsin and the transfer of nutrients.

2. Cones:

The basic structure is similar to that of rod cells. The main differences are: the cones have large nuclei and light staining, except for the fovea, located in a single row near the outer membrane; the outer protrusion is called the cone, and the It is slender, about 75 m long, and about 1 to 1.5 m in diameter. It is thicker and shorter at the periphery of the retina, about 40 m long. The cone is also divided into outer and inner segments. The outer segment is conical, the membrane disk at the bottom is large, and it gradually decreases toward the top. All the membrane disks are always connected to the cell membrane. The protein synthesized in the inner segment enters the outer segment and does not form a new membrane disc, but diffusely supplements and renews the protein components of the membrane disc. The ends of the medial protrusions swell into a foot shape, called the cone foot, and bipolar cells Form multiple synapses with horizontal cells, some synapses are triple synapse complexes, and some are general synapses. There are three types of cone cells in the human retina, and their diaphragms contain red, blue, and green sensitive pigments. The change process of these optochromes after exposure to light is basically similar to rhodopsin, but its synthesis and decomposition process is unknown. Red (green) color blindness is caused by the lack of red (green) visual pigment in the retina.