What Are the Different Parts of the Eyeball?

The eyeball is the main part of the sight, which is located in the orbit, and the back end is connected to the mesencephalon by the optic nerve. The human eyeball is approximately spherical, with an anterior-posterior diameter of about 24 to 25 mm. The median point of the anterior cornea of the eyeball is the anterior pole, the median point of the posterior sclera is the posterior pole, and the straight line connecting the anterior and posterior poles is the external axis of the eye.

The eyeball is the main part of the sight, which is located in the orbit, and the back end is connected to the mesencephalon by the optic nerve. The human eyeball is approximately spherical, with an anterior-posterior diameter of about 24 to 25 mm. The median point of the anterior cornea of the eyeball is the anterior pole, the median point of the posterior sclera is the posterior pole, and the straight line connecting the anterior and posterior poles is the external axis of the eye.

Chinese name

eyeball

Foreign name

eyeball

Pinyin

yn qiú

lie in

In the orbit

rear end

Optic nerve is connected to the brain

Construct

Eyeball wall and contents

Eyeball overview

The line from the front pole of the cornea to the back pole of the retina is the intraocular axis, which is about 22mm long. The extension line passing through the inner and outer axes of the eye is collectively called the eye axis. From the points equal to the front and back poles, the circular lines made around the surface of the eyeball are called the equator or mid-latitude line. The straight line passing through the center of the pupil to the center of the macula is the visual axis. The optic axis intersects with the eye axis to form an angle of about 5 °. The eyeball consists of the eyeball wall and transparent contents. The refractive system of the eyeball includes the cornea, aqueous humor, lens, and vitreous body; the photosensitive system is that the wall of the eyeball is composed of three layers of outer, middle and inner films.

Eyeball Anatomy Explanation

The outer membrane is an eyeball fibrous membrane, which is thick and tough, protects the eyeball and maintains the shape of the eyeball together with the contents of the eye. Its anterior 1/6 is cornea, transparent and slightly convex, with a thinner central portion and thicker periphery. The anterior corneal radius of curvature is 7.84mm, which is an important refractive device with a refractive index of 1.3771. The cornea has no blood vessels, and nutrients come from the limbal vascular network and the infiltration of aqueous humor. The cornea is rich in nerve endings and is the most sensitive part of the whole body. The posterior 5/6 of the adventitia is the sclera, which is milky white in adults, thick and opaque. The sclera is anteriorly connected to the cornea and the rear is continuous with the optic nerve sheath. The junction of the cornea and sclera is the limbus. In the sclera near the limbus, there is a scleral sinus (infusion ring), which is a tubular tissue lined with endothelium around the anterior chamber angle. It is directly connected to the venous network in the sclera through 25 to 35 efferent tubules, and is the drainage path of aqueous humor. In the posterior part of the sclera, there is a circular zone through which the optic fiber bundles pass. It is the sieve plate and is the weakest point of the sclera.

The middle membrane is the vascular membrane of the eyeball, which contains blood vessels and pigments. It nourishes the eyeballs and forms a dark box that shields the light inside the eyeballs. It is conducive to light and color sensing. The choroid occupies the last 2/3 of the median membrane and is a thin, soft, brown membrane that lies between the sclera and the retina. The anterior ciliary body passes through the optic nerve at the rear. The outer surface of the choroid is connected to the sclera loose, with a choroidal space in between, and the inner surface is in close contact with the retinal pigmentation. Choroids are rich in blood vessels and pigments. The ciliary body is anteriorly connected to the root of the iris and the subsequent choroid is a hypertrophy with a width of 5 to 6 mm. The ciliary body and the ciliary band support the position of the lens, adjust its curvature, and are related to the production of aqueous humor. The front of the ciliary body bulges as a ciliary crown, and there are more than 70 radially arranged protrusions on the inside of the ciliary body as ciliary processes, which are rich in blood vessels and can produce aqueous humor. The rear part of the ciliary body is flatter as a ciliary ring, and the thin ridges arranged radially are ciliary ridges. There are ciliary muscles in the ciliary body, which contains three groups of smooth muscle fibers: longitudinal fibers near the sclera, radial fibers in the middle, and circular fibers in the front. When the near object is seen, the ciliary muscle contracts, the ciliary body moves forward and inward, relaxes the ciliary zonula, increases the curvature of the lens, and plays a close-adjusting role. When looking at distant objects, the ciliary muscles relax, the ciliary body moves backward, the ciliary zonula is tightened, and the curvature of the lens decreases. The iris is a continuation of the ciliary body forward and inward. It is a ring-shaped film with a diameter of about 12mm and a circular pupil in the center. The iris of the camera decreases or widens with the intensity of the light, and adjusts the amount of light entering the eye. The inner edge of the iris is called the pupil edge, and the outer edge is called the ciliary edge. The iris contains two sets of smooth muscles: a circular pupil sphincter close to the pupil edge can reduce the pupil; a pupil opened radially from the periphery of the iris to the pupil to open the great muscles, which can open the pupil. The number and distribution of pigments in the iris determine the color of the iris, which can be brown-black, blue, or gray, etc., and vary by race.

The intima is the retina, which is divided into three parts: the retinal iris part, the ciliary body part, and the visual part. The first two parts are attached to the inner surface of the iris and the ciliary body respectively. They have no nerve components and are not sensitive. They are called blind retinas. The retinal vision is attached to the inner surface of the choroid, the optic nerve is connected posteriorly, and the anterior serpentine margin is connected to the blind region. It is a nerve tissue membrane and has a photosensitive effect. It is divided into two parts, internal and external (histologically divided into 10 layers). The outer part is the pigmented part, which is close to the choroid; the inner part is the nerve part. There is a potential gap between the two layers, and the retinal detachment is the separation of the nerve from the pigmentation. The nerve department consists of three layers of cells from the outside to the inside: the optic cell layer, the bipolar cell layer, and the ganglion cell layer. There are photoreceptor cells in the visual cell layer. There are about 111 to 125 million rod cells and about 6.5 to 7 million cone cells. These two kinds of cells contain chemical substances that absorb light energy, which can convert light energy into chemical energy and electrical energy, and produce nerve impulses. Most of the rod cells are distributed around the retina, and can sense dark light. The cone cells are mainly concentrated in the macula, and can sense daylight and have color vision. The bipolar cell layer is mainly composed of bipolar cells. In addition, there are horizontal cells outside the myopia cell layer, and there are amacrine cells at the near ganglion cell layer. The latter two are horizontally connected contact cells. Bipolar cells connect optic cells and ganglion cells vertically. The ganglion cell layer contains ganglion cells, which are multipolar neurons, whose axons converge into the optic nerve and penetrate the posterior wall of the eyeball into the brain.

The inner surface of the back of the eyeball is the fundus. Fundus can be used to observe the fundus phase. The normal fundus shows a uniform orange-red color. There is an optic disc at about 3mm inside the posterior pole of the eyeball. It has a light red disc shape and a diameter of about 1.5mm. The axon collection site, ignoring cells, is not sensitive, is the physiological blind spot of the retina. The central part of the optic disc has a disc depression, and the central retinal arteries and veins are distributed in the retina through the optic disc. On the temporal side of the retina, about 3.5 mm from the disc depression, there is a yellowish cell slightly below the macula with a diameter of about 2 mm. The center is slightly concave, that is, the fovea. The retina at the bottom of the concave is the thinnest, and the cone cells are dense. Long, other layers of cells and blood vessels pass around the peripheral edge of the fovea, so that the incident light reaches the sensitive and sensitive macular cone cells. Here each cone cell forms a one-to-one connection with a single bipolar cell and ganglion cell, so foveal vision is the sharpest and most accurate.

Eyeball contents include aqueous humor, lens, and vitreous. External light is refracted through the cornea and transparent contents, focused on the fundus retina and imaged, and then converted into optical impulses by the photoreceptive energy conversion of the visual cells, which is transmitted to the visual center of the brain via the optic nerve and optic channels. To produce vision.

The eye chamber is the cavity between the cornea and the lens that contains the aqueous humor. The iris separates it into a larger anterior chamber (between the cornea and the iris) and a smaller posterior chamber (between the iris and the lens). The anterior and posterior chambers communicate through the pupils. The annular area at the junction of the iris and the cornea is the iris corneal angle or anterior chamber angle. On the deep side of this corner, there are many trabecular structures like iris angular comb ligaments, and the reticular space between trabeculae is the iris angular gap, also known as the Fontana cavity. The aqueous humor is filled in the eye chamber and is produced by the ciliary body. It reaches the anterior chamber of the eye through the posterior chamber of the eye and the pupil, then enters the scleral sinus through the anterior chamber angle and iris angle space, and finally enters the vein. Aqueous humor is a colorless and transparent water-like liquid with a total amount of 0.2 to 0.3 ml and a refractive index of 1.3374. In addition to the refractive effect of aqueous humor, it also nourishes the cornea and lens and maintains intraocular pressure.

The lens is a biconvex elastic transparent body. The back is more convex than the front. It is located between the iris and vitreous body, without blood vessels and nerves. The lens is surrounded by a lens capsule, which is transparent and elastic. The lens capsule is suspended on the inner side of the ciliary process by the ciliary band. The lens capsule surrounds the lens body composed of multiple layers of lens fibers. The outer periphery is softer and the fibers are more elastic. It is a lens cortex. The central portion is denser and harder, and the elasticity is also poor. It is the lens core. The refractive index of the lens is about 1.4371. The lens relies on its elastic retraction to increase convexity and enhance refractive power. With age, the elasticity of the lens weakens, and the regulating force also weakens, which results in "presbyopia".

The vitreous body is a transparent and colorless colloid, which is filled between the lens and the retina. The vitreous body occupies 4/5 of the inner cavity of the eyeball. The refractive index was 1.3360.