Introduction
The human eye is like a camera: light passes through the cornea and aperture (pupil), and is then focused by the lens (crystal) onto the film (retina). The human eye is approximately spherical and is located in the orbit. The average anteroposterior diameter of normal adults is 24mm, and the average vertical diameter is 23mm. The front end protrudes 12-14mm beyond the orbit and is protected by the eyelid. The following is a schematic diagram of the eye structure, let’s take a look at the knowledge of the eye structure diagram!
Eye appearance structure diagram
Eyes are the windows to the soul, and each of us has a pair of eyes. However, not all of us fully understand the structure of the eye. The picture shows the appearance structure of the eye.
The eyelid is located in front of the eyeball, divided into upper and lower eyelids, and the crack between the eyelids is called palpebral fissure. It is an important structure to protect the eyeball. Eyelashes, also known as eyelashes, are neatly arranged hairs that grow on the eyelid strings, and have the function of blocking foreign objects and protecting the eyeballs. The corner of the eye refers to the angle between the upper eyelid and the lower eyelid of the human eye. Usually, the corner of the eye refers to the area of the eye. Schematic diagram of the eyeball structure
The eyeball is approximately spherical and is located in the orbit. The average anteroposterior diameter of normal adults is 24mm, and the average vertical diameter is 23mm. The front end protrudes 12–14mm outside the orbit and is protected by the eyelid. The eyeball includes the eyeball wall, the inner cavity and contents of the eye, nerves, blood vessels and other tissues.
The outer layer of the eyeball wall
The outer layer consists of the cornea and sclera. The first 1/6 is the clear cornea, the remaining 5/6 is the white sclera, and the transition between the two is the corneal and scleral limbus. The outer layer of the eyeball maintains the shape of the eyeball and protects the tissues inside the eye.
Cornea The cornea is the transparent part of the front of the eye through which light enters the eye. The cornea is slightly oval and slightly protrudes forward. The horizontal diameter is 11.5~12mm, and the vertical diameter is about 10.5~11mm; the peripheral thickness is about 1mm, and the center is 0.6mm; the front curvature radius is 7.8mm, the back is about 6.8mm, and the refractive index is equivalent to a +43D lens. The cornea is divided into:
a. Epithelial cell layer: This layer has strong regeneration ability, and no traces are left after the damage is repaired;
b. > c, parenchymal layer: important in optical system;
d, Descemet’s layer: rapid regeneration after injury;
e, endothelial cell layer: with cornea-atrial Water barrier function, damage cannot be regenerated.
The cornea is avascular and is nourished by tears, aqueous humor, peripheral blood vessels and nerve branches; the corneal surface receives oxygen from the atmosphere; the tear film in front of the cornea has the functions of preventing corneal drying, maintaining corneal smoothness and optical properties The role of; cornea is rich in nerves, sensitive. Therefore, in addition to being the main structure for light entering the eye and refraction imaging, the cornea also plays a protective role and is an important part of measuring human perception.
Sclera The sclera is a dense structure of collagen fibers, opaque, milky white, and tough in texture. The front is connected to the cornea and the back is connected to the optic nerve dura.
The sclera includes the episclera, the sclera parenchyma, and the brown-black layer. The medial side where the front end combines with the cornea forms the anterior chamber angle and is an important part of the aqueous humor circulation; the sclera surface is covered by the eyeball fascia and conjunctiva; The sclera is the attachment point of the extraocular muscles, where the sclera is the thinnest, 0.3 mm, and the rest is about 1 mm thick.
The middle layer of the eyeball wall
The middle layer, also known as the uveal membrane, is rich in pigment and blood vessels, including the iris, ciliary body and choroid.
The iris is circular in shape, in the most anterior part of the uvea, in front of the lens, with radial folds called texture, and the surface contains uneven crypts. There is a 2.5~4mm circular hole in the center, called the pupil. The pupillary size is regulated by the annular pupillary sphincter (parasympathetic innervation) and pupil dilator muscle (sympathetic innervation). The pupil shrinks under light, called anti-light reflex. The ciliary body connects to the root of the iris anteriorly, the choroid posteriorly, the sclera outside, and the equator of the lens through the suspensory ligament inside. The ciliary body includes ciliary muscle, abundant blood vessels, and trigeminal nerve endings, which are innervated by parasympathetic nerves. It secretes aqueous humor, which is related to intraocular pressure and tissue nutrient metabolism; the ciliary body also adjusts the diopter of the lens through the suspensory ligament to see far and near objects clearly. The choroid is located between the sclera and the retina. The blood circulation of the choroid nourishes the outer layer of the retina, and the rich pigments it contains play a role in shading the darkroom. The inner layer of the eyeball wall
The inner layer is the retina, which is a transparent membrane and the first stop for the transmission of neural information formed by vision. It has a very fine network structure and rich metabolic and physiological functions.
The outer side of the retina is the choroid, the inner side is the vitreous body, anteriorly to the serrata, posterior edge of the ciliary body, and posteriorly to the optic disc.
The serrated edge is located at the front of the retina, 6 mm behind the corneal and scleral limbus. It is also the anterior attachment site of the retina and is connected to the pars plana.
The visual axis of the retina ends directly at the fovea. The macular area is a special area with the sharpest vision on the retina, with a diameter of about 1~3mm, and its center is a small concave, namely the fovea. The macula is thin, with no blood vessels in the center, and the orange-red choroid beneath it can be seen through. Here are mainly cone cells.
A light red area with a diameter of 1.5mm is located about 3mm on the nasal side of the macula. The optic disc is mostly vertical oval, reddish in color, with a clear border, with arteriovenous branches on it, and a small depression in the center called the optic cup or physiological depression. The optic disc is the beginning of the transmission bundle of the combination of nerve fibers and has no photoreceptor cells, so it appears as an inherent dark area in the visual field, which is called the physiological blind spot.
The retina is divided into 10 layers from outside to inside: pigment epithelium layer, visual cell layer, outer membrane, outer granular layer, outer subordinate layer, inner granular layer, inner subordinate layer, ganglion cell layer, nerve fibers layer, inner limiting membrane.
Intraocular cavity and contents Intraocular cavity The intraocular cavity includes the anterior chamber, posterior chamber, and vitreous cavity.
The anterior chamber is bounded by the cornea anteriorly, the iris and lens posteriorly, and the anterior chamber angle at the periphery. The central part is 2.5~3.0mm deep and the periphery is shallow. The volume of the human eye is about 0.2ml. The posterior chamber is anteriorly bounded by the iris, surrounded by the ciliary process, and posteriorly by the anterior lens capsule and the suspensory ligament. The aqueous humor is secreted by the non-pigmented epithelium of the ciliary process into the posterior chamber and flows through the pupil into the anterior chamber. Adult volume is about 0.06ml. The vitreous cavity is the largest cavity in the eye, anteriorly bounded by the lens, suspensory ligament, and ciliary body, and posteriorly bounded by the retina and optic nerve. The volume is 4.5ml.
Eye contents Eye contents include aqueous humor, lens and vitreous. All three are transparent and together with the cornea are called the refractive medium.
Aqueous humor is produced by the ciliary process, nourishes the cornea, lens and vitreous, and maintains intraocular pressure. The lens is an elastic transparent body, shaped like a biconvex lens, located behind the iris, pupil, and in front of the vitreous body, and is connected with the ciliary body by the lens suspensory ligament to fix the position. The radius of curvature is 10mm at the front and 6mm at the back. As the lens grows with age, the nucleus of the lens increases and becomes hard, the elasticity of the capsule weakens, and the accommodation power decreases, showing presbyopia. The vitreous body is a transparent colloid that fills the cavity of the posterior 4/5 of the eyeball. The main ingredient is water. There is a concave surface called the vitreous concave in front to accommodate the lens, and the rest is attached to the retina and ciliary body. The vitreous has a refractive function and also supports the retina. No regeneration capability.
