What are the parts of the human eye and their functions? How do the eyes work? Discover the intricate details of eye anatomy in this in-depth article.

Exploring the Intricate Anatomy of the Human Eye

The human eye is a marvel of nature, a complex organ that allows us to perceive the world around us in remarkable detail. From the protective outer layer to the delicate inner structures, each component of the eye plays a vital role in the process of vision. In this comprehensive guide, we will delve into the 16 key parts of the eye and uncover their respective functions, shedding light on the remarkable workings of this remarkable organ.

The Conjunctiva: Protecting the Eye’s Surface

The conjunctiva is a thin membrane that covers the sclera, or the white portion of the eye, as well as the interior of the eyelids. This structure serves as a protective barrier, shielding the eye from harmful substances and microorganisms. Inflammation of the conjunctiva, known as conjunctivitis or “pink eye,” can lead to various eye disorders, including pinguecula, pterygium, and subconjunctival hemorrhages.

The Sclera: Providing Stability and Protection

The sclera, commonly referred to as the “whites” of the eye, covers more than 80% of the eyeball’s surface. This sturdy, flexible structure provides stability and protection for the eye’s inner workings. The sclera is surrounded by a thin layer of tissue called the episclera, which contains small blood vessels that nourish the sclera. When the sclera or episclera becomes inflamed, the conditions of scleritis and episcleritis can occur, leading to redness, eye pain, blurry vision, and lid swelling.

The Iris: Regulating Light and Focusing Vision

The iris is the colored part of the eye, unique to each individual. This structure is located between the cornea and the lens, and its primary function is to regulate the amount of light that reaches the retina. The iris exhibits a “pupillary light reflex,” in which it narrows in bright light and opens in low light. Additionally, the iris performs the “accommodation reflex,” which allows the eye to shift focus from nearby to distant objects by adjusting the pupil’s aperture, the shape of the lens, and the convergence of the eyes.

The Pupil: Controlling Light Entry

The pupil is the black opening in the center of the iris that allows light to enter the eye. The size of the pupil adjusts to control the amount of light that reaches the retina, enabling the eye to function effectively in various lighting conditions. The difference between the centers of the pupils is known as the pupillary distance, an important factor in vision and the proper fitting of eyeglasses.

The Cornea: Refracting Light and Protecting the Eye

The cornea is the clear, protective outer layer of the eye. It not only acts as a barrier against harmful substances and microorganisms, but it also plays a crucial role in vision. The dome-shaped surface of the cornea refracts, or bends, light as it passes through the eye, enabling the eye to focus on objects effectively. Additionally, the cornea can filter out some of the sun’s harmful ultraviolet (UV) light, although wearing sunglasses is still recommended to prevent long-term damage.

The Uvea: Controlling Light Adaptation and Object Distance

The uvea is the middle layer of the eye, located beneath the sclera. It is composed of three parts: the iris, the ciliary body, and the choroid. These structures work together to control the eye’s adaptation to varying levels of light and the ability to focus on objects at different distances. If any of these structures become inflamed, the resulting condition is known as uveitis.

The Choroid: Nourishing the Retina

The choroid is a vascular layer located between the sclera and the retina. Its primary function is to deliver nourishment, in the form of blood and oxygen, to the outer layers of the retina. This vital supply of nutrients keeps the retina functioning effectively, allowing the eye to perceive and process visual information.

The Lens: Focusing Light on the Retina

The lens is a transparent, flexible structure located behind the iris. Its primary function is to focus the light entering the eye onto the retina, enabling sharp, clear vision. The lens is capable of changing shape, a process known as accommodation, to adjust the eye’s focus from near to distant objects.

The Vitreous Humor: Maintaining Eye Shape and Clarity

The vitreous humor is a clear, jelly-like substance that fills the space between the lens and the retina. This substance helps maintain the eye’s shape and provides support for the retina. Additionally, the vitreous humor helps to keep the eye clear and free from obstructions, allowing light to reach the retina unimpeded.

The Retina: Transforming Light into Electrical Signals

The retina is a light-sensitive layer of tissue located at the back of the eye. It contains two types of photoreceptor cells, known as rods and cones, which are responsible for converting the light that enters the eye into electrical signals. These signals are then transmitted through the optic nerve to the brain, where they are interpreted as the images we see.

The Optic Nerve: Transmitting Visual Information to the Brain

The optic nerve is the bundle of nerve fibers that carries the electrical signals from the retina to the brain. This vital structure is responsible for transmitting the visual information processed by the eye to the visual cortex, where it is interpreted and perceived as the world we see.

The Lacrimal System: Maintaining Eye Lubrication and Cleanliness

The lacrimal system is the set of structures responsible for producing, distributing, and draining the tears that keep the eye lubricated and clean. This system includes the tear glands, tear ducts, and the tear drainage system, all of which work together to ensure the eye’s proper function and protection.

The Eyelids and Eyelashes: Protecting the Eye’s Delicate Surface

The eyelids and eyelashes play a crucial role in protecting the eye’s delicate surface. The eyelids open and close to blink, which spreads tears across the eye and removes debris. The eyelashes, on the other hand, help to filter out dust, dirt, and other particles that could potentially harm the eye.

The Extraocular Muscles: Controlling Eye Movement

The extraocular muscles are a set of six muscles that are attached to the outside of the eye. These muscles work together to control the eye’s movement, allowing us to focus on objects and track moving targets. The precise coordination of these muscles is essential for maintaining binocular vision and depth perception.

The Sinus Cavities: Providing Support and Protection

The sinus cavities surrounding the eye, known as the orbital sinus, provide additional support and protection for the delicate structure of the eye. These air-filled cavities help to cushion the eye and shield it from external impacts, reducing the risk of injury.

The Blood Supply: Nourishing the Eye’s Tissues

The eye is supplied with blood through a network of arteries and veins, which provide the necessary nutrients and oxygen to the various tissues and structures within the eye. This blood supply is essential for maintaining the eye’s health and proper function.

In conclusion, the human eye is a remarkable and complex organ, comprised of numerous intricate parts, each with its own vital function. By understanding the anatomy and physiology of the eye, we can better appreciate the incredible processes that allow us to perceive and interpret the world around us. With this knowledge, we can take steps to protect and maintain the health of our eyes, ensuring a lifetime of clear and vibrant vision.

16 Parts of the Eye & Their Functions

How Do the Eyes Work?

The eyes work in the same way as cameras.

Light is reflected when you focus on an object and enters the eye through the cornea. As the light passes through, the dome-shaped nature of the cornea bends light, enabling the eye to focus on fine details.

In addition to the retina, other visual components such as the pupil, iris (colored part of the eye), and lens help focus light rays on the retina.

When light entering the eye hits the retina, special cells known as photoreceptors convert it into electrical signals.¹

The optic nerve carries these electrical impulses from the retina to the visual cortex (in the brain). The brain then interprets the impulses into the images you see.

Eye Anatomy (16 Parts of the Eye & What They Do)

The following are parts of the human eyes and their functions:

1. Conjunctiva

The conjunctiva is the membrane covering the sclera (white portion of your eye). The conjunctiva also covers the interior of your eyelids. 

Conjunctivitis, often known as pink eye, occurs when this thin membrane becomes inflamed or swollen. 

Other eye disorders that affect the conjunctiva include:

• Pinguecula (accumulation of protein and fat deposits in the conjunctiva)
• Pterygium (a noncancerous growth that develops on the conjunctiva)
• Subconjunctival hemorrhages (broken blood vessels)

2. Sclera

The sclera is sometimes known as the “whites” of the eye. It covers more than 80% of the eyeball’s surface.² 

On the exterior, the sclera is smooth and white, but on the inside, it is brown and has grooves that help properly attach the eye tendons. The sclera provides stability and protection for the eye’s inner workings but is also flexible. This allows the eye to move as needed to see different objects.

The episclera is a thin layer of tissue on top of the sclera. The episclera has tiny blood vessels that supply the sclera with nutrients. 

When the sclera gets inflamed, the condition is referred to as scleritis.³ If the episclera is inflamed, the resulting condition is known as episcleritis. These conditions can cause redness, eye pain, blurry vision, and lid swelling.

3. lris

The iris is the colored part of the eye and is unique to each person. This structure is located in the front of the eye, between the cornea on the outside and the lens on the inside. 

The iris primarily regulates how much light reaches the retina by controlling the size of the eye’s “window,” or pupil. 

As a result, it exhibits what is known as a “pupillary light reflex,” in which it narrows in bright light while opening up in low light.

The iris also performs what is known as the “accommodation reflex.” This is the eye’s instinctive ability to shift focus from nearby to distant objects.

This action requires adjusting the pupil’s aperture (opening), the shape of the lens, and convergence (the ability of the eyes to work together).

4. Pupils

The pupil is seen as a black dot in the center of the iris. 

The pupil is essentially a hole that allows the eye to focus on the things in front of it. They open and close to regulate the amount of light that enters the eye. 

Light enters the eye via the lens, which focuses light rays through the pupils into the retina. The difference between the centers of your pupils is called your pupillary distance.

5. Cornea

The cornea is the clear and protective outer layer of your eye. Together with the sclera (the white of your eye), the cornea acts as a barrier against dirt, infectious microorganisms, and other substances that can damage the eye.

In addition to protection, the cornea also plays a significant role in vision. Considering the dome shaped surface of the cornea, this structure refracts (bends) light as it passes through the eye. This enables it to focus on objects effectively.

The cornea can filter out the sun’s harmful ultraviolet (UV) light. This prevents some UV light from reaching other structures inside the eye. However, to prevent damage to the cornea and other parts of the eye, you should wear sunglasses. 

Chronic exposure to UV light may lead to inflammation and other complications, including cancer.⁴

6. Uvea

The uvea is the eye’s middle layer. It is located underneath the white part of the eye (the sclera) and is composed of three parts:

• The iris
• Ciliary body
• Choroid

These structures control some eye functions, such as adapting to varying levels of light or object distances.

If any structures become inflamed, the resulting condition is called uveitis.

7. Choroid 

This vascular layer is located between the sclera and retina of your eye. It delivers nourishment (through blood and oxygen supply) to the retina’s outer layers. 

In short, the choroid is the source of life that keeps the retina functioning effectively.

The choroid reflects light, which causes the red-eye effect in photographs.

8. Retina

The retina is a sensitive membrane that covers your eye’s rear surface. Images are transmitted to the retina when your eye picks up the images.

The retina converts these images into impulses, which are sent to your brain through the optic nerve. This enables you to see and interpret what you see.

Some of the ocular conditions that affect the retina include:

• Diabetic retinopathy. Diabetes complication caused by damaged blood vessels.
• Retinal detachment. When the retina detaches from its normal position.⁵
• Retinitis pigmentosa. Deterioration of special light-sensitive cells in the retina.
• Retinoblastoma. Formation of cancer cells in the retinal tissues.

9. Eye Muscles

The eye has six muscles. These muscles arise from the eye socket (orbit) and work to move the eye up and down, side to side, or in a circular motion.

The six eye muscles are as follows:

1. The superior rectus. Attaches to the top of the eye and moves the eye upwards.
2. The inferior rectus. Attaches to the bottom of the eye and allows downward eye movement.
3. The medial rectus. Attaches to the side of the eye adjacent to the nose and helps the eyes to shift inwards towards the nose.
4. The lateral rectus. Attaches to the outer side of the eyes and moves the eyes toward the temples.
5. The superior oblique. It originates from the back of the eye socket and attaches to the top of the eye. It rotates the eye inwards (front to back) and downwards.
6. The inferior oblique. It arises from the front of the socket near the nose and travels inwards, attaching to the bottom surface of the eyeball. It rotates the eye outwards (front to back) and upwards.

10. Macula Lutea

Light rays are focused on the macula lutea when an eye looks directly at an object.  

The macula lutea is a yellow oval area in the retina’s center (back of the eye). The center of the macula is known as the fovea.

The section of the retina is in charge of sharp, detailed central vision (also called visual acuity). 

The macula lutea has a high concentration of cones. These are the light-sensitive retinal cells that provide high visual acuity. 

11. Eye Lens

The lens of the eye (or crystalline lens) is the transparent lentil-shaped structure inside your eye. This is the natural lens.

It is located behind the iris and to the front of the vitreous humor (vitreous body). The vitreous humor is a clear, colorless, gelatinous mass that fills the gap between the lens and the retina in the eye. 

The lens is held in place by a fibrous membrane known as zonule of Zinn or the lens suspensory ligaments.⁶The lens changes its thickness and curvature, allowing the eye to focus on objects from varying distances.

If your lens has an irregular curvature, you’re more prone to develop astigmatism. Cataracts are another lens-related visual disorder in which the lens becomes opaque or hazy, impairing vision.

12.

Aqueous Humor

Aqueous humor is a fluid substance that fills the eye. It’s divided into two chambers. The anterior chamber is in front of the iris, whereas the posterior chamber is right behind it. 

These layers enable the eye to keep its shape. This liquid is evacuated via the Schlemm canal to eliminate any accumulation in the eye.

Glaucoma may develop if a person’s aqueous fluid does not drain adequately.

13. Ciliary Body

The ciliary body is a ring-shaped tissue found behind the iris. It attaches to the lens through the zonular fibers (fibers of Zinn).

The ciliary body holds and regulates the eye lens’s movement, keeping the lens shape intact.

This structure is also involved in the production of aqueous humor.

14. Optic Nerve

The optic nerve is a bundle of about 1.2 million nerve fibers that transmit visual information to the central nervous system (brain).⁷

There is one nerve per eye connecting each eye to the brain. Vision loss may occur if any of the nerves are damaged.

However, the consequences of optic nerve damage depend on the extent of the damage. 

15. Optic Disc

The optic disc is where the axons of retinal ganglion cells join together and mark the beginning of the optic nerve (second cranial nerve). 

The optic disc also serves as the entrance site for major blood vessels that nourish the retina.

In the average person, the optic disc carries about 1.2 million nerve fibers from the retina to the brain.

16. Fovea Centralis

The fovea Centralis (central fovea) is a tiny depression in the retina that houses cones that help with proper vision. It is located within the macula.

Approximately 80-90% of the optic nerve fibers convey visual information from the fovea, while the other portion conveys information from the peripheral retina.  

If there are any issues with the fovea of the cones, you may experience blurry vision.

Summary

Learning about the eye’s anatomy helps you understand the complex working mechanism and unique structure involved in each task. Any defects in the eye structures are likely to affect your ability to see and overall eye health.

For this reason, it’s important to take good care of your eyes. If you notice any unusual changes in your ability to see, a visit to your eye doctor (optometrist) is important.

In this article

An easy guide to your eye’s anatomy

Your Eye’s Surface

1. Eyelid

What is it?
Your eyelid is a thin fold of skin, lined with a row of eyelashes. Each eye has an upper and lower eyelid, and they can be opened and closed by special muscles.

What does it do?
The eyelids are vital to keeping your eyes healthy. By completely covering the front of your eye, they are able to block debris or impurities that may otherwise cause damage or infection.

Just as importantly, your eyelids help to prevent the surface of your eyes from drying out. They do this by regularly spreading tears when blinking, keeping the cornea moist.

2. Sclera

What is it?
You might better know the sclera by its more common name – the “white of the eye”. As its nickname suggests, this is the white part of your eye that surrounds the iris.

What does it do?
The sclera helps to support and protect the structure of your eye. It’s made up of tough tissue, which ensures your eyeball keeps its shape.

Thanks to the sclera’s hardiness, the eyeball is less susceptible to injury than if it were surrounded by a softer tissue. It also provides support to the inside of your eye, by providing a surface for some of the ocular muscles to attach to.

3. Tear Duct

What is it?
The nasolacrimal duct is known to you and me as the tear duct. It’s the area found in the corner of your eyes, closest to the nose.

What does it do?
Your tear ducts carry excess tears away from the surface of your eyes. These tears are carried through to an area inside your nose called the nasolacrimal duct.

This explains why when you’re crying or suffering from watery eyes due to an allergy, you can sometimes taste the salt from your tears in your mouth. It’s also the reason why you might find your nose goes runny from crying.

4. Lacrimal Gland

What is it?
The lacrimal glands are shaped a bit like an almonds, found in the upper part of your eye sockets. You’ve got two lacrimal glands, one located just above each eye.

What does it do?
The basic function of your lacrimal glands is to produce tears. The secreted tears are collected on the conjunctiva of your upper eyelid.

Tears help to nourish and moisten your cornea (the outer layer of your eye’s surface). They also keep your eye clean, and lubricate it to avoid irritation.

5. Conjunctiva

What is it?
The conjunctiva makes up the lining inside your eyelids. It almost entirely covers your sclera, and is nourished by tiny blood vessels that are almost invisible to the naked eye.

What does it do?
The conjunctiva acts as a vessel for your tears to be spread over the surface of your eye. This is important for ensuring your eyes are properly lubricated.

Conjunctivitis, also known as pinkeye, is a common condition associated with the conjunctiva. It occurs when the conjunctiva becomes inflamed, usually due to some sort of infection.

6. Pupil

What is it?
The pupil is the small black hole found in the centre of your eye. It is surrounded by the colourful iris, and leads directly to the inside of your eye.

What does it do?
The pupil acts as an entry point for light to enter your eye. Surrounding muscles in the iris, called the pupillae, adjust the pupil’s size automatically depending on light conditions.

In light conditions, your pupil will probably be around 3mm in diameter. In total darkness, this diameter can extend to over 6mm. This allows more light into your eye, allowing you to see more clearly in dimmer environments.

7. Iris

What is it?
The colourful ring found in the middle of your eye is called the iris. It’s made up of tiny pigment cells called melanin, which determine the colour of your eyes.

What does it do?
Your iris surrounds the pupil, and contains muscles that are able to alter its size. During light conditions, your iris causes the pupil to lessen in size. In darkness, the iris enlarges in order to allow more light to enter your eye.

The iris also acts as a wall that separates the anterior chamber (between cornea and iris) from the posterior chamber (between the iris and crystalline lens).

Inside Your Eye

1. Cornea

What is it?
The cornea is a thin layer that covers the iris, pupil and anterior chamber. A healthy cornea is completely transparent, so that it can allow light through to the pupil.

What does it do?
Your cornea has a number of important roles. It is able to focus incoming light, making up around two-thirds of your eye’s total optical power.

Your cornea also protects the iris and pupil, preventing foreign objects from entering the inside of your eye. Additionally, it acts as a light filter, screening out many of the sun’s harmful rays and stopping them from reaching your retina where they’d otherwise cause damage.

2. Crystalline Lens

What is it?
The crystalline lens is a transparent structure that’s convex on both sides and suspended by tiny suspensory ligaments. It’s located just behind your iris, and is not visible from the outside without special viewing apparatus.

What does it do?
The surrounding ciliary muscles adjust the shape of the crystalline lens, allowing it to focus incoming light. This ensures that images are sharply focused on the retina at the back of your eye.

As the ciliary muscles contract, the suspensory ligaments that hold the lens in place relax. This causes the lens to assume a more spherical shape, allowing you to see close objects. When the muscles relax, the lens becomes flatter to allow you to focus on more distant objects.

3. Ciliary Body

What is it?
The ciliary body surrounds and is attached to the crystalline lens. Circular in shape, it separates the posterior chamber from the vitreous.

What does it do?
There are three main components that make up the ciliary body: the suspensory ligaments (zonules), ciliary muscle and ciliary processes. The ligaments and muscle work together in order to alter the shape of the crystalline lens and adjust how light is focused in your eye.

The ciliary processes produce aqueous humour. This is a transparent fluid that fills the anterior and posterior chambers of your eyes.

4. Retina

What is it?
Your retina is a light-sensitive layer that coats the inner part of your eye. It has a direct connection to your brain via the optic nerve.

What does it do?
Without the retina, your eye would have no way of interpreting the incoming light. When light hits the back of your eye, the retina processes and converts the energy into electrical signals.

The electrical signals are then sent to your brain through the optic nerve, ultimately translating into the images we see.

5. Macula

What is it?
Found on the surface of your retina, the macula is a sensitive, circular area that appears a bit darker than the space around it.

What does it do?
The macula contains a large amount of photoreceptors in comparison to the rest of retina. This means that it is suited to interpreting higher levels of and colour, providing the bulk of your central vision.

In a healthy eye, the macula is responsible for anything that requires the ability to see detail clearly. This might include reading or seeing the detail in someone’s face.

6. Optic Disc

What is it?
The optic disc marks the beginning of the optic nerve as it enters the back of your eye. Only a few millimetres from the centre of your retina, a healthy optic disc is slightly oval in shape.

What does it do?
Because the optic disc is where the optic nerve has first contact with your retina, this is the point where the visual information begins its journey to the brain.

There aren’t any photoreceptors on the surface of your optic disc. Because of this, it is unable to process any visual information. This is the reason behind the ‘blind spot’ in your vision.

7. Central Retinal Vein and Artery

What are they?
The central retinal vein and artery line the back of the retinal wall. Healthy veins and arteries should appear consistent in width, with a deep red colour.

What do they do?
Your retina requires a blood supply in order to function. This is where the central retinal vein and artery comes in.

The central retinal artery supplies blood through the sclera, before branching out across the retina. Meanwhile, the central retinal vein carries blood and other waste products away from the retina. Both initially travel through the optic nerve in order to reach the retina.

8. Optic Nerve

What is it?
The optic nerve travels from your brain, all the way to the back of the eye. The point at which it meets your retinal wall is known as the optic disc.

What does it do?
This is like the USB cable of your eye. After light has been converted into information by the retina’s photoreceptors, it is transmitted along the optic nerve.

It’s formed of around 1.2 million nerve fibres, that work together to send the impulses that will ultimately be processed into a visual image. The right side of your brain receives information from the left visual field of both eyes, while the left side receives information from the right visual field.

9. Vitreous

What is it?
Around 80% of your eyes’ total mass is made up of vitreous. This is a clear gel that fills the space between the crystalline lens and your retina.

What does it do?
The vitreous’ main function is to exert pressure on the inside of your eye. This helps to keep the layers of your retina tightly pressed together, as well as maintaining the general structure of the eyeball.

Your vitreous is completely stagnant, with no blood vessels to carry waste away. This means that anything that enters your eye will remain there unless surgically removed, possibly obscuring vision.

Now that you have a better understanding of how the eye works why not take a look at our vast range of eye care products. We have amazing products including eye drops, contact lens solutions & accessories that can help you maintain good eye health.

Eye socket, structure, description, definition.

The eye socket (orbit) is a bony cavity, which is a reliable protection for the eyeball.

The orbit, or the bony orbit, is a bony cavity that is a reliable protection for the eyeball, auxiliary apparatus of the eye, blood vessels and nerves. The four walls of the orbit: upper, lower, outer and inner, are firmly interconnected.

However, each of the walls has its own characteristics. So, the outer wall is the strongest, and the inner, on the contrary, is destroyed even with blunt injuries. The peculiarity of the upper, inner and lower walls is the presence of air sinuses in the bones that form them: the frontal one from above, the ethmoid labyrinth inside and the maxillary sinus from below. Such a neighborhood quite often leads to the spread of inflammatory or tumor processes from the sinuses into the cavity of the orbit. The eye socket itself is connected to the cranial cavity through numerous holes and fissures, which is potentially dangerous when inflammation spreads already from the eye socket to the side of the brain.

The structure of the orbit

The shape of the orbit resembles a tetrahedral pyramid with a truncated top, having a depth of up to 5.5 cm, a height of up to 3.5 cm and a width of the entrance to the orbit of 4.0 cm. Accordingly, the orbit has 4 walls: upper, lower , internal and external. The outer wall is formed by the sphenoid, zygomatic and frontal bones. It separates the contents of the orbit from the temporal fossa and is the strongest wall, so that the outer wall is rarely damaged during injuries.

The upper wall is formed by the frontal bone, in the thickness of which, in most cases, the frontal sinus is located, therefore, with inflammatory or neoplastic diseases in the frontal sinus, they often spread to the orbit. Near the zygomatic process of the frontal bone there is a fossa in which the lacrimal gland is located. At the inner edge there is a notch or a bone hole – the supraorbital notch, the exit point of the supraorbital artery and nerve. Near the supraorbital notch there is a small depression – a trochlear fossa, near which there is a trochlear spike, to which the tendon block of the superior oblique muscle is attached, after which the muscle abruptly changes the direction of its course. The upper wall of the orbit borders on the anterior cranial fossa.

The inner wall of the orbit, for the most part, forms a thin structure – the ethmoid bone. Between the anterior and posterior lacrimal crests of the ethmoid bone there is a recess – the lacrimal fossa, in which the lacrimal sac is located. Below, this fossa passes into the nasolacrimal canal.

The inner wall of the orbit is the most fragile wall of the orbit, which is damaged even with blunt injuries, due to which, almost always, air enters the tissue of the eyelid or the orbit itself – the so-called emphysema develops. It is manifested by an increase in tissue volume, and when palpated, the softness of the tissues is determined with the appearance of a characteristic crunch – the movement of air under the fingers. In inflammatory processes in the area of ​​the ethmoid sinus, they can quite easily spread into the cavity of the orbit with a pronounced inflammatory process, while if a limited abscess is formed, it is called an abscess, and a widespread purulent process is called phlegmon. Inflammation in the orbit can spread towards the brain, and therefore be life-threatening.

The lower wall is formed mainly by the upper jaw. From the posterior edge of the lower wall, the infraorbital groove begins, continuing further into the infraorbital canal. The lower wall of the orbit is the upper wall of the maxillary sinus. Fractures of the lower wall quite often occur with injuries, accompanied by the omission of the eyeball and infringement of the inferior oblique muscle with limited mobility of the eye upward and outward. With inflammation or tumors located in the sinus of the upper jaw, they also quite easily pass into the orbit.

The walls of the orbit have many openings through which blood vessels and nerves pass, which ensure the functioning of the organ of vision. Anterior and posterior ethmoid openings – located between the upper and inner walls, through them pass the nerves of the same name – branches of the nasociliary nerve, arteries and veins.

Inferior orbital fissure – located in the depth of the orbit, closed by a connective tissue septum, which is a barrier that prevents the spread of inflammatory processes from the orbit to the pterygopalatine fossa and vice versa. Through this gap, the inferior ophthalmic vein leaves the orbit, which then connects with the pterygoid venous plexus and the deep facial vein, and the inferoorbital artery and nerve, the zygomatic nerve, and the orbital branches extending from the pterygopalatine nerve ganglion enter the orbit.

The superior orbital fissure is also covered with a thin connective tissue film, passing through which three branches of the ophthalmic nerve enter the orbit – the lacrimal nerve, the nasociliary nerve and the frontal nerve, as well as the trochlear, oculomotor and abducens nerves, and the superior ophthalmic vein exits. The gap connects the orbit with the middle cranial fossa. In case of damage in the region of the upper orbital fissure, most often injuries or tumors, a characteristic complex of changes occurs, namely, complete immobility of the eyeball, ptosis, mydriasis, slight exophthalmos, a partial decrease in the sensitivity of the skin of the upper half of the face, which occurs when the nerves passing through the fissure are damaged, as well as dilation of the veins of the eye due to a violation of the venous outflow along the superior ophthalmic vein.

Optic canal – bony canal connecting the orbital cavity with the middle cranial fossa. Through it, the ophthalmic artery passes into the orbit and the optic nerve exits. The second branch of the trigeminal nerve, the maxillary nerve, passes through the round hole, from which the infraorbital nerve separates in the pterygopalatine fossa, and the zygomatic nerve in the inferior temporal fossa. The round foramen connects the middle cranial fossa with the pterygopalatine.

Next to the round hole is an oval hole connecting the middle cranial with the infratemporal fossa. The third branch of the trigeminal nerve passes through it – the mandibular nerve, but it does not take part in the innervation of the structures of the organ of vision.

Methods for diagnosing diseases of the orbit

• External examination with an assessment of the position of the eyeballs in the orbit, their symmetry, mobility and displacement with light finger pressure.
• Feeling the outer bony walls of the orbit.
• Exophthalmometry to clarify the degree of displacement of the eyeball.
• Ultrasound diagnostics – detection of changes in the soft tissues of the orbit in the immediate vicinity of the eyeball.
• X-ray, computed tomography, magnetic resonance imaging – methods that determine the violation of the integrity of the bone walls of the orbit, foreign bodies in the orbit, inflammatory changes and tumors.

Symptoms in diseases of the orbit

Displacement of the eyeball relative to its normal location in the orbit: exophthalmos, enophthalmos, displacement upwards, downwards – occurs with injuries, inflammatory diseases, tumors, changes in the blood vessels in the orbit, as well as endocrine ophthalmopathy.

Impaired mobility of the eyeball in certain directions – observed in the same conditions as previous disorders. Edema of the eyelids, redness of the skin of the eyelids, exophthalmos is observed in inflammatory diseases of the orbit.

Reduced vision, up to blindness – possible with inflammatory, oncological diseases of the orbit, trauma and endocrine ophthalmopathy, occurs when the optic nerve is damaged.

The structure of the lens of the eye | CCO “Medinvest”

Building

The lens is located inside the eyeball, right behind the pupil. According to its chemical properties, it is a crystalline protein. Biologically, it is epithelial cells that are strongly elongated in length. And each of them is a transparent hexagonal prism.

Protein molecules are large, so the body is not transparent. Despite its protein structure, it transmits light rays through itself.

In the center it is dense, closer to the periphery it becomes smaller. It consists of:

• capsules

• epithelium

• base material

Let’s give a definition to each. The capsule is an elastic transparent shell that has a protective function. The capsule is thicker in front than behind. It is attached with an elastic ciliary band or ciliary ligament. He suspends the lens, fixing it on the ciliary body.

Epithelium is a layer of non-keratinized cells. Cells are closely pressed to each other in the center and practically do not divide. Cells are more active if they are closer to the periphery. On it, they begin to divide and form a growth zone. And new fibers appear in this zone. As new fibers appear, the old ones move closer to the center where the nucleus is formed. As a result, it changes and its size and density increase. For this reason, in people over 45, near vision becomes worse.

Properties

Babies are born with a soft globular lens. Its refractive power is estimated at 35.0 diopters. Over time, it increases in diameter. In an adult, it becomes 10 mm in diameter and 5 mm in thickness. The refractive power of a lens that is at rest is 19 diopters. If it is in tension, the increase reaches 33 diopters.

Accommodation

The lens is able to change the optical power, this ability is called accommodation. Thanks to it, a person is able to see at a short distance. Accommodation decreases in a person due to age, and closer to 60 years it becomes almost zero. Because of this, age-related farsightedness develops.

Parts of the eye are not transparent, but due to the elasticity of the lens and its ability to change curvature and thickness, people get a clear image.

Causes of cataracts

The lens, like any other part of the body, receives nutrients and excretes waste, which occurs through the capsule. There are no capillaries and nerves in the lens itself, and lymph does not flow.

A certain liquid composition washes the lens. If the chemical index of this composition changes, the lens will not be able to receive the elements it needs and the oxidative reaction will slow down. As a result, it turns out to be cloudy. Doctors call this disease a cataract. Unfortunately, it is very common. It mostly appears after 50 years. It can also be congenital or acquired as a result of an injury.

Atrophy

Reducing the volume of an organ due to lack of nutrition is called atrophy. That is a dystrophic process. Lack of nutrients threatens to shrink cells and tissues. Cells can slow down, or even die, if they don’t get enough oxygen. Then they are excreted from the body, having previously broken down into molecules.

This happens, but in good conditions the cells are renewed. But with dystrophy, new cells do not appear. And in order for the organ to remain in a normal size, the remaining cells expand. The disease affects the eyeball completely, or individual structures. It does not affect the size of the lens, but the optical function may disappear.

This may be due to:

Ophthalmologists treat disease with medication or surgery. The main thing is to treat the underlying cause, because problems in the organs of vision are a consequence. often the results of therapy are not positive and the lens is replaced with an IOL.

Lens replacement

Lens replacement is a reliable way to treat cataracts and atrophy. Once it was not replaced, but moved to free the pupil. And there was a hole behind it.

This affected the optical power and its quantity. Visual acuity was then 2-3%. The beam fell on the retina, but was not focused, and people after the operation did not see clearly.

But another way of treatment has already appeared. Invented artificial lenses. They are identical to the natural optical system. This method of implantation was carried out in 1949. But there were still complications, since the implant touched the cornea. The operation required a long rehabilitation. But now it is being changed differently. The implant is fixed by the iris, so it does not move into the vitreous body and does not cause discomfort.