Outline of eye anatomy and physiology

2021-02-02 12:00 AM

The sclera is made up of many layers of thick, crisscrossed tape that are responsible for protecting the membranes and the internal environment.

The eyes are the sensory organs that carry out the visual function. Thanks to the human eye, it is new to learn and recognize the surrounding environment, creating conditions for growing intelligence.

The structure of the eye includes 3 parts: the eyeball, the eye protector, the nerve pathway and the visual analysis centre.

Ring bridge

The eyeballs are spherical, the axial length in adults is 22-24 mm. Short or long eyeballs will cause near-sighted or farsighted spherical refractive errors.

Eyeball sheath

Corneal:

Picture: Cornea structure

It is a very chewy, transparent membrane that has no capillary-shaped blood vessels that occupy the a fifth of the anterior part of the eyeball's shell.

The diameter of the cornea is about 11 mm, the radius of curvature is 7.7 mm. The thickness in the center is 0.5 mm, on the edge is 1mm. Refractive power is about 45D.

Organizational aspect of cornea has 5 classes, from the outside to the inside, including:

Epithelium: is the non-horny stratified epithelium.

Bowman membrane: acts as the basal membrane of the epithelium.

Parenchyma: occupies 9/10 corneal thickness - Cartesian membrane: very tough.

Endothelium: only one cell layer.

The cornea is nourished by osmosis from the blood vessels around the edges, from tears and water.

The nerve that governs the cornea sensation is composed of branches originating from the eye nerve (V1).

Sclerosis:

The sclera is a very chewy, white fibrous tissue that accounts for 4/5 behind the eyeball. The sclera is made up of many layers of thick, crisscross tape that are responsible for protecting the membranes and the internal environment.

The thickness of the sclera varies depending on the region. The thickest sclera is in the posterior polar region (1 - 1.35mm), the thinnest is in the grip of the squamous muscles, only about 0.3mm. At the edge, the sclera thickness is 0.6mm and at the equator is 0.4 - 0.6mm. The posterior sclera has a hole with a diameter of 1.5mm to cover the hole with a sieve with many small holes for the optic nerve fibers to pass.

The choroid

The choroid, also known as the uvea, consists of three parts, the iris, the eyelid, and the black desert. In which the iris and the eyelid body are called the anterior uvea and the black desert is called the posterior uvea. The common job of the uvea is to nourish the eyeball and regulate the eye pressure.

Iris:

The iris has a punctured coin in the middle. The front is the rear limit of the front room, and is brown, blue or black according to race. The back of the iris has a uniform dark brown color and is the front limit of the back room. In the middle of the iris is a circular hole called the pupil.

About iris histology consists of 3 main classes:

The endothelium is in the front, contiguous with the endothelial layer of the cornea.

Buffer layer: is a spongy wick organization with two types of smooth muscle fibers, the pupil sphincter, which is the pupil contraction, dominated by the III nerve and the spinal muscle relaxes the pupil, due to the wire the dominant sympathetic nerve. In this layer there are also pigment cells that determine iris color.

The posterior epithelium, consisting of highly dense pigmented cells, gives the back of the iris a dark brown color.

The main role of the iris is to regulate the amount of light reaching the retina through changing the size of the pupil.

Lids:

The ciliary body is the protrusion of the uvea between the iris and the black desert. The role of the ciliary body is to regulate the eyes to see nearby objects and to secrete aqueous humor through cubic cells in the eyelash.

The lids hidden behind the iris are an irregular circular band, the temples and upper (5.6 to 6.3 mm) wider than the nose and below (4.5 to 5.2 mm). The thickness is 1.2 mm. The cross-section of the ciliary body is a triangular shape, the apex facing the dark cornea, the base facing the center of the cornea, one edge facing anterior to the sclera and one edge facing the vitreous, the base of the iris. latch on.

From the back, you may have 2 parts. The smooth, pale posterior part called the orbicular ciliaris bounds behind this region as ora serrata. The anterior part, called corona ciliaris, has about 70 to 80 folds called eyelashes. Light gray fringes stand out against the dark brown background of the lashes. From here there are transparent ligaments that travel to the equator of the vitreous body called the Zinn ligaments.

In terms of organization, you have 7 classes from outside to inside:

Lids: continuous with the supernatant.

Ciliary body layer: consists of longitudinally arranged smooth muscle fibers (Bruck muscle) and sphincter (Muller muscle).

The vascular layer: grows very richly in the eyelashes.

Glass film: transparent.

Pigment epithelial layer: consists of cylindrical cells containing many myeline located on the glass membrane.

Ciliary epithelium: is composed of non-pigmented cylindrical cells. the longer cells in the back near the ora serrata, the longer the cells are, the closer they are to the eyelash, the shorter these cells will become cubes.

Inner bound class: is the innermost layer.

Desert:

A loosely connected membrane between the sclera and the retina. The retina has many blood vessels and dark pigment cells that feed the eyeballs and turn the eyeballs into a dark chamber that makes the image clearly visible on the retina.

Regarding the organization of learning, there are 3 classes:

The supernatant layer is outside

The genuine layer of the wall has lots of blood vessels

Bruch membrane in the same

Blood vessels and nerves of the uvea:

Arteries: The uvea consists of two systems, the short-ciliary arteries behind the posterior ciliary arteries. The posterior short-ciliary artery consists of about 20 arteries originating in the ocular artery through the sclera around the optic nerve and then branched into the choroid. The posterior ciliary arteries have 2 arteries, after entering the eyeballs by penetrating the sclera on either side of the optic nerve, these 2 arteries pass through the mesothelioma, not branching to the cornea, but going. straight to the outer edge of the iris branching to form a large artery ring of the iris that governs the iris and the ciliary body.

Veins: Blood from the uvea follows the small veins and then converts to 4 large veins called veins extracted out of the eyeball along the eye veins flowing into the cavernous sinus.

Lymph: absent in the uvea

Nerve: There are 2 types of fibers, namely, the long eyelid nerve and the short eyelid nerve that penetrates the sclera at the posterior end of the eyeball around the optic nerve to enter the chord. The long eyelid nerve consists of 2 fibers originating from the nasal branch of the V1 cord (the eye branch of the thalamus nerve). The short eyelid nerve is composed of fibers that originate from the ciliary (eye node).

The eyelid is located in the eye socket, behind the eyeball, outside the optic nerve and is made up of three types of fibers, the sympathetic fibers coming from the cervical sympathetic ganglion, the sensory fiber of the nasal branch of the V1 nerve and the motor fiber belonging to No. III nerve.

Retinal

The retina is also called the nerve membrane, located in the lumen of the uvea. That is the place to receive light stimuli from the outside and then transmitted to the visual analysis center in the cortex.

Shape:

Retina consists of 2 parts is the retina and the sensory retina, the boundary between the two parts is Ora - Serrata 7 - 8 mm from the edge of the cornea.

The center of the retina, corresponding to the posterior pole of the eyeball, is a light-colored area called the macula. In the center of the macula, there is a small recessed hole called the central fovea.

At 3.4 to 4 mm from the macula to the nose is the papillae us, which is the starting point of the optic nerve. The papillae are round or slightly oval in shape, about 1.5 mm in diameter, pale pink in color, and clearly delineated with the surroundings.

Structure:

The retina has 4 layers of cells:

Pigment epithelial layer includes only 1 cell layer located adjacent to the choroid. These cells are flat hexagonal, small nucleus, cytoplasm with many pigments. at the base of the cell there are elongated cytoplasmic strips that form filaments of 5m length.

Visual cells: these are sensory cells. The outer polarity of these cells differentiates into a photoreceptor embedded in the filaments of the pigment epithelium. The inner poles of these cells are connected to bipolar cells. There are two types of photoreceptors: cones and rods. Cones help us to perceive subtle images of objects in full light conditions, these cells also help us perceive colours. Rod cells help you see in low light conditions.

The physiological activity of cones and rods is due to the effects of chemicals such as Iodopsin in the cones and Rhodopsin in the rod cells.        

Rhodopsin  Rétinen + Protein

Iodopsin Vitamin A + Protein

The distribution of cones and rods is not uniform in the retina. The cone cells are mainly located in the central retinal region and gradually decrease towards the periphery. Rod cells are located mainly in the peripheral retina.

Bipolar cell layer: It is responsible for transmitting nerve impulses from light-receptor cells to ganglion cells. There are two types of cells, polynomial bipolar cells that receive impulses from multiple visual cells and synaptic bipolar cells that receive impulses only from one visual cell.

Ganglion cells or poly solar cells: are quite large cells, size 20-30m. Each cell has many dendrites in contact with bipolar cells, in particular in the macular each polypole cell is connected to only a single bipolar cell. Each ganglion cell has a very long axon, all of the axons are directed towards the papillae to form the optic nerve.

Blood vessels of the retina:

The central retinal artery is a branch stemming from the eye artery running to the eyeballs, about 10mm from the posterior pole of the eye, entering the optic nerve, along the optic nerve axis to go to the retina. Reaching the disc, this artery splits into two branches: the upper and lower branches, each branching into the temples and nasal branches. These branches continue to bisect as though branches are not in succession.

The veins usually come parallel to the arteries. The venous papillae are usually located on the outer side of the artery. Once out of the eyeball, the central vein of the retina continues to exit the optic nerve, usually slightly behind the artery. The vein then continues through the butterfly slit above the Zinn ring, eventually pouring into the cavernous sinus.

Room charge and back room

Room charge:

The anterior chamber is a space between the cornea in the front, the iris and the vitreous body in the back, filled with aqueous humor.

The center of the anterior room is the deepest place, the depth here is about 3 - 3.5 mm. Closer to the edge, the pre-room depth decreases. The depth of the anterior chamber also changes with age, the older this depth decreases as the volume of the glass body increases. The presbyopia, the short axial eye, is usually very shallow. In contrast, in the myopia, the anterior chamber is usually wider and deeper than the average person.

The anterior angle at the outer edge of the anterior chamber is limited by the cornea - the sclera anteriorly and the iris - the posterior lumen, which is also called the corneal iris angle.

The anterior chamber is an area of ​​physiological as well as surgical importance because this is where most absorbed aqueous humor escapes the anterior chamber and most intraocular surgeries have to pass through this area. The front room corner has the following components:

Schwalbe ring: is a small ring-shaped ledge, where the end of the Cartesian membrane.

Trabeculae: is a triangular prismatic strip, light gray in the depths of the scapula - cornea. Trabeculae is composed of many stacked fibers forming a system of pore holes so that the aqueous humor can escape to the Schlemm tube.

The Schlemm tube: located behind the trabeculae, is responsible for collecting fluid and then pouring it into the general circulatory system of the body.

Sclera: The junction between the sclera and the cornea. Sclera is often obscured by trabeculae, so it is rarely seen during angiogram.

Lashes: is the visible part of the lash line, represented by a thin dark border.

The iris base: is the place where the iris clings to the lids

Backroom:

The anterior chamber has the anterior limit of the posterior iris and the posterior limit is the front of the vitreous membrane (Hyaloid membrane). The back room is connected to the anterior chamber through the pupil, in the back room also contains aqueous humor like the front room.

Transparent environments

Hydrology:

Aqueous humor is a clear liquid secreted by the eyelids that fills the anterior and rear room.

Ingredients of aqueous humor

The main component of aqueous humor is 98.75% water, in addition Albumin and Globulin 0.02%, Glucose 0.008%, amino acids 0.03%, in addition there are electrolytes, mucopolysaccharide, oxygen ....

Circulation of the aqueous humor

The aqueous humor is secreted by the cubic cells of the ciliary body, then most of the aqueous humor (80%) passes through the pupillary hole to the anterior chamber, then the aqueous humor passes through the trabeculae structure at the corner of the anterior chamber to the Schlemm tube. then follow the water veins to the mesothelioma and into the general circulatory system of the body. The remainder of the aqueous humor (20%) is absorbed through the uvea to the parietal upper cavity and then absorbed by the capillaries there.

The role of aqueous humor

Fluid is the most important factor affecting intraocular pressure. Thanks to the eye pressure, the eyeballs are always in a stable shape, ensuring the optical function of the eye. At the same time, aqueous humor is a source of nutrition for the vitreous body and plays an important role in nourishing the cornea.

Glass form:

Shape

The vitreous is a biconvex transparent lens that is fixed to the lash area by means of Zinn wires. The thickness of the glass is about 4mm, the diameter of 8-10mm, the radius of the curvature of the front is 10mm, the back side is 6mm. Optical power is 20-22D.

The vitreous body has 2 front and back faces, where these two sides meet is called the equator. The front is adjacent to the back of the iris, the back is adjacent to the vitreous membrane. The vitreous equator is about 0.5 mm away from the lumen, where there are transparent ligaments connecting from the outer edge of the vitreous to the ciliary body called the Zinn ligaments that hold the vitreous in place and transmit. the activities of the ciliary body to the vitreous membrane.

Organizational structure

The vitreous body consists of 3 parts:

Wrapping film: also called a vitreous capsule, is a transparent, chewy and elastic membrane that covers the outside of the vitreous body.

Sub meal epithelium: This epithelium has only one cell layer and is present only in the front. in the front center of these cells are flat, but closer to the equator, these cells tend to ascend, narrow and gradually elongate, turning into glass fibers.

Vitreous fibers: each vitreous fiber is an elongated epithelial cell. These strands bend like a U, the bottom facing the equator, the head facing the center. The fibers connected to the opposite charge fiber in the center form a Y-joint on the front and an inverted Y on the back of the vitreous body.

Fiberglass fibers are produced endlessly throughout life. The newly created fibers push the old fibers into the center, causing the glass to thicken and form a hard central nucleus in people over 35 years old. More software is located around a hard core called a vitreous shell.

Blood vessels and nerves

The vitreous body has absolutely no blood vessels and nerves. Nourishing the vitreous body is through selective osmosis of the aqueous humor. When the vitreous is damaged, the aqueous humor will infiltrate into the vitreous body massively, making the vitreous quickly cloudy and swollen.

The role of the vitreous body

The focusing power of the vitreous body plays an important role in the refractive system, helping the pixel to focus properly on the retina when viewed from afar. The ability to change the thickness of the vitreous body is called a regulation that helps the eyes to see nearby objects clearly.

Glass translation:

A liquid like egg whites behind the vitreous, occupying the entire posterior part of the eyeball, the outer layer thickens into a Hyaloid membrane. In people under 35 years the Hyaloid membrane and vitreous form stick together, while in people over 35 years the Hyaloid membrane and the vitreous body split into the Berger void.

The main component of the vitreous is a fibrous structural protein called Vitrain and fills in the spaces between the fibers, Hyaluronic acid.

Eyeballs protectors

Eye socket

There are two eye sockets located on either side of the nasal cavity, made up of the skull and facial bones. The eye sockets are pyramidal with four ribs, the base facing forward and the top facing back.

Size:

In adults, the volume of the socket averages about 29 ml. The height from the top to the bottom of the eye socket is 40 mm. The width of the base of the eye socket is approximately 40 mm, the height of the base is approximately 35 mm.

The walls of the eye socket:

Citadel on

Also known as the orbit ceiling, it is formed by the frontal brow bone and the small wing at the back. Outside of the orbit, ceiling is tear hole, in which there is a major tear gland. Inside, near the inner upper corner, there is a pulley hole located 4 mm behind the edge of the eye socket, where the sticking of the large cross muscle pulley is attached.

Outside

This wall is very thick, made up of three bones. The front has the cheekbones below and the outer eye socket above. Behind are large butterfly bones

The lower wall

Also known as the base of the eye socket. This wall is made up of the eye sockets of the female palate, the cheekbones and the apex of the upper jaw bone. The base of the eye socket is only about 0.5 - 1 mm thick, so it is easy to be damaged when there is facial injury that creates the communication between the fovea and the maxillary sinus.

Inner city

This wall has four bones including the lateral surface of the sternum, the plane of the sieve bone, the tear bone and the outer apex of the frontal bone.

The eye sockets are surrounded around the sinuses. Therefore, sinusitis can be the cause of a number of eye diseases.

Picture: Eye socket

The bottom of the eye socket:

The bottom of the eye socket has an oval shape with 4 banks

The upper shore

At the point between the inner and outer 2/3 of the upper bank is the concave of the pulley with the artery in the pit and the frontal nerve passing through. The inner angle has the outer nasal nerve. The outer 1/3 have arteries and tear nerves.

Outer shore

There is a ligament attached to the outer ligament, the other end of the ligament attaches to the cartilage.

The lower bank

The slightly sunken bone on the outer 1/3 creates a fairly wide space below the outer eyeball, which is a convenient location for parenteral injection. Below the midpoint of the lower bank about 1cm there is a hole in the fossa, passing through here is a branch of the maxillary nerve that governs the feeling of the lower lids called the pitotomy.

Inner shore

The bones are rolled up into a trough called the tear canal.

The top of the eye socket:

There are a visual hole and a V-shaped slit. Through the optic hole, there is nerve number II in the central artery of the retina. Clinging to the inner edge of the visual hole has a large upper lash lift muscle and cross muscle.

The V-shaped cleft has 2 parts: the upper part is called the butterfly slit; the lower part is the jaw-butterfly groove. Clinging to the centre of the V-shaped slot is a fibre ring called a zin ring. Pass through the zin ring to enter the socket with upper and lower branches of nerve III, nerve VI and nasal nerve. Pass through the upper part of the sequential butterfly slit with the tear nerve, frontal nerve, eye veins and IV nerve. Located in the fissure of the jaw has the fossa branch of the maxillary nerve.

The elements located in the eye sockets:

The motor of the eyeball

There are 6 muscles of the eye, including 4 straight muscles, which are straight upper, lower straight, inner straight, and outer straight and 2 are big cross muscle, baby cross muscle.

Principle: Four straight muscles clinging to the Zinn ring at the top of the eye socket. Large cross muscle clinging inward on the visual hole, the baby cross muscle clings to the lower corner in the eye sockets.

Adhesion: The upper, outer, lower and inner orthostatic muscles stick to 8mm, 7mm, 6mm and 5mm edges respectively. The large cross muscle clings to the outer top of the posterior eyeball, the posterior end of the line clinging to the macula 2mm. The baby's cross muscle clings to the outside of the posterior eyeball.

The movements: the upper muscles bring the eyes up, the lower straight muscles bring the eyes down, the straight muscles bring the eyes in, the outer muscles bring the eyes out. The big cross muscles bring the eyes down, out and inwards, the baby cross muscles bring the eyes up, out and outwards.

The dominant nerve: The straight upper, the inner, the lower and the baby cross muscles are dominated by the III nerve, the outer straight muscle dominated by the VI nerve, the large cross muscle dominated by the IV nerve. .

The muscles of the eyelids

Upper eyelid muscle: This muscle comes from the fibrous tissues at the top of the eye socket that is facing forward, located close to the ceiling of the orbital. When approaching the base of the eye socket, the body expands and ends with a wide tendon in the eyelid.

Lash-sphincter: The muscle fibres surrounding the eyelash close the eyes. The muscles have two parts: the eye sockets and the eyelids. The dominant muscle is a branch of the facial nerve.

The tendons in the eye sockets

Perioral fibromyalgia: A thin fibrous membrane mixed with strong, smooth muscle fibres that encapsulate the bone walls of the fovea and connects to the sclera through the optic canal and fissure.

Tenon: The fibrous membrane that covers the sclera begins behind the cornea and ends at the entrance of the optic nerve. At the attachment of the tenon envelope muscles, the posterior envelope covers the muscles and sticks to the muscle sac. 3 mm from the edge of the cornea, tenon envelopes begin to stick to the conjunctiva into a single leaf.

Eye pit organization

It is a rich vascular fatty tissue that fills the remaining gaps in the eye sockets to help reduce the shock of the eyeballs when we are active.

Eyelids

Each eye has 2 lashes, upper and lower lashes. Anatomy of 2 lashes is nearly the same.

Eyelid structure:

The eyelids have 4 layers, from front to back, including:

Lashes: thin and smooth. The sweat glands in the skin are tubular called the Moll glands

The lash muscle layer: includes the sphincter and the upper lash lift muscle.

The sphincter attaches to the ligaments of the inner and outer ligaments. The sphincter that is located close to the edge of the lash line is called the Riolan muscle. The eyelid sphincter is dominated by the number VII nerve, which closes the eyelashes and closes the eyes. Paralysis VII causes Charles-Bell syndrome.

The upper lash lift muscle comes from the top of the eye socket to the front, the muscle fibres cling to the skin of the eyelash and the upper margin of the ciliary cartilage. The upper eyelid lift muscle dominated by the III nerve opens the eyes. When damage to the upper III lash line collapses, it causes collapse syndrome.

Cartilage layer: essentially this is a fibrous organization that the fibres are pressed tightly, giving them a solid density like cartilage. There are two cartilage sheets, the upper and lower lash cartilage, creating a relatively solid frame for the eyelid. In the ciliary cartilage, there are the sebaceous glands of Meibomius, there are about 25 35 glands in each eyelid, the gland emptying out of the free margin of the eyelid.

Conjunctiva: is a thin inner membrane with many blood vessels. Conjunctivitis has 3 parts: conjunctiva, conjunctiva with map and conjunctiva of the eye. Scattered in the conjunctiva there are secondary tear secreting glands: Manz gland, Henlé gland ... Conjunctivitis circulation due to 2 different circulatory systems. The shallow system is derived from the posterior conjunctival artery, running from the same map anteriorly. The deep system is derived from the anterior ciliary artery or the motor artery.          

Eyelash circulation:

Artery

The main circulation originates from the artery in the pit, consisting of the upper and lower ciliary artery.

The auxiliary circulation that nourishes the peripheral lids originates from the tear artery, the temporal artery ...

Vein

Blood flows from the lids into the venous system around the eye socket and then into the cavernous sinus.

Motor nerves and lash sensation:

Motor

Nerve number VII governs the sphincter, the number III nerve governs the upper eyelid lifting muscle.


Picture: Eyelids.

Feeling

The upper lash sensation is due to the tear branch, forehead, nose are all branches of the V1 cord dominated. The sensation of the lower lids is dominated by the foveal nerve.

Disregard

Tear moderators:

The job of tears is to nourish and protect the cornea. Tears are secreted from the main tear gland located in the upper outer corner of the eye socket and the tear gland is scattered in the conjunctiva.

Tear path:

Tears are collected into the upper and lower tear holes in the inner lids of the upper and lower eyelids and then go through the common tear canal to the tear pocket. From here, the tears continued to go through the disorganized tear duct pouring down the nose in the lower nasal passages.

Picture: Tear Gland

Nerve pathways and visual centre

The optic nerve pathway

The axons of the ganglion cells are concentrated to the papillae, which pass through the sieve to form the optic nerve (line II). The optic nerve travels to the top of the fovea and then goes through the optic hole into the skull. The axons of the ganglion cells of the nasal half of the retina (nasal bundle) cross to the opposite side to accompany the bundle of the other temples to stop at the outer knee. The place where the two bunches of the nose cross each other is called the visual interference, located just above the pituitary, so when the pituitary is enlarged, it will damage the very specific market.

The segment from the interference to the pillow body outside the fibres tends to spread wider than the previous one, so it is also called the visual band. From the outer knee, the optic fibers continue to expand like a fan, so it is called the optic ray to stop at the occipital cortex.

 Circulation of the visual track is guaranteed by 3 arteries including the Sylvius artery, the anterior artery and the posterior cerebral artery. Damage to these arteries will damage the corresponding visual line, allowing the location and expected cause of the injury.

The visual centre in the cerebral cortex

Consists of the 17, 18 and 19 cortical regions of the occipital cortex, around the astragalus and partially encroaching on the outer surface of the occipital lobe. Area 17 is also known as the Brodmann area