Ultimate Guide to Eye Anatomy: Parts, Structure, Functions & Diagram

Overview of Eye Anatomy

An eye is a part of an organism that helps it see things. It takes in light and turns it into signals for the brain. In fancy terms, it is an optical system that collects light, adjusts its intensity, focuses it to form an image, and sends signals to the brain. Eye anatomy consists of various parts that make it a prime and important human body part. There are two main types of eyes: compound and non-compound. Compound eyes, found in insects, have many small visual units. Non-compound eyes, like those in mammals, including humans, have one lens and form a single image on the retina.

You are born with two eyes that work together to give you a wide field of view, depth perception, and color vision. If the focus is right, things look clear. But your eye muscles can adjust to get the focus spot-on.

When light hits your retinas, special cells send messages to your brain about what they see — the color, brightness, and details. Your brain then decodes these messages to create the images you see.

Eye Anatomy Diagram

Parts of Eye

Eye Anatomy: Parts, Names & Functions

Cornea

The cornea is like a clear shield covering the front of your eye. It protects against dirt, germs, and UV rays while also helping to focus light for vision.

It sits in front of a watery chamber in your eye. If it gets damaged, it can heal quickly. However, it is important to protect it since it is vulnerable to injury. It has six layers, each with a specific job.

1. Epithelium: This is the outermost layer and serves as a barrier against the outside world. It is very sensitive to pain, helping you react quickly to protect your eyes.
2. Bowman’s layer: Made mostly of collagen, this tough layer provides structure and helps the cornea maintain its shape.
3. Stroma: This is the thickest layer and strengthens the cornea while also helping to focus light onto the retina.
4. Pre-Descemet’s layer (PDL): Also known as “Dua’s layer,” it is airtight, creating a strong barrier between the inside of the eye and the outside environment.
5. Descemet’s layer: This thin but strong layer protects the inside of the eye from injury and infection.
6. Endothelium: Responsible for maintaining fluid balance within the cornea and the eye, ensuring proper function.

Together, these layers work like laminated glass in car windshields, providing strength and protection to the eye.

The laminated glass consists of layers of glass with a plastic sheet in between. The layers of the cornea work together to make it resilient and efficient.

Iris

The iris is the colorful part of your eye that controls the black opening called the pupil. This pupil lets light into your eye. The color of your iris is unique to you, like a fingerprint.

The iris has two layers: one at the front with pigment that gives it color and one underneath with muscles.

There are two main muscles: the sphincter pupillae, which makes the pupil smaller by squeezing it, and the dilator pupillae, which makes it bigger by pulling the iris apart.

The iris adjusts the size of your pupil. When it is wider, more light gets in, and when it is narrower, less light gets in. It helps you see better in different lighting conditions, like going from bright sunlight to indoors.

Your iris automatically adjusts your pupil size to help you see clearly, a process called the pupillary light reflex.

The iris is really good at blocking light because of its pigmented layers, ensuring that only the right amount of light reaches the retina at the back of the eye.

Some people are born without an iris, which can make their vision blurry, but their eyes still work.

Pupil

The pupil is a black hole in the middle of your eye, which adjusts in size based on how much light there is. In bright light, it gets smaller; in dim light, it gets bigger.

It is called the pupillary light response. The pupil is part of your vision system, letting light into your eye. The cornea and conjunctiva protect it.

Muscles in your iris control the size of your pupil. There are two: the iris dilator opens it, while the iris sphincter closes it. Light enters through your pupil, gets focused by the lens, and hits the retina at the back of your eye.

The retina turns light into signals for your brain, which then forms images. Nerves connect your pupil to your brain, controlling its size.

The pupil also provides a pathway for aqueous humor, a fluid that nourishes your eyes, to flow to the front of your eye. Humans have round pupils, but other animals have different shapes, like slits or rectangles.

Lens

The lens of the eye is like a clear, flexible ball behind the colored part (iris) and in front of a gel-like substance. It is about 10 mm wide and 4 mm deep in adults.

Made mostly of proteins, it is transparent and can change shape to focus light on the retina, giving us clear vision. This bending of light helps us see things clearly at different distances.

When light enters the eye, the lens bends it to create a focused image on the retina. But this image is upside down or reversed. Don’t worry! The brain fixes it.

Little muscles around the lens help it change shape for focusing. Plus, there are tiny fibers keeping it in place.

The lens stays healthy with a clear fluid called aqueous humor.

It doesn’t need nerves or blood; this fluid gives it energy and keeps it clean. It flows through the eye and drains out to keep everything running smoothly.

Ciliary Body

The ciliary body is a component of the eye that sits underneath the colorful iris. It looks like a ring with folds called ciliary processes, which create clear fluid. This fluid covers the gap between your cornea and iris, supplying pressure and nutrition to your eye.

The ciliary body has two primary functions: producing fluid and changing the lens shape for focusing. It is linked to the iris and affects the lens shape via zonular fibers.

As you concentrate, the ciliary body aids the lens in changing form. When looking at something close, the lens becomes rounded; when looking far, it flattens out. This modification is essential for clean eyesight.

Presbyopia, which makes it difficult to focus on nearby things as we age. The changes in the ciliary body cause it.

Overall, the ciliary body is part of the uvea, along with the iris and choroid, working together to support vision by controlling light and lens shape.

Retina

The retina is like the camera film in your eye. It is a layer at the back of your eyeball and catches the light that comes in.

Inside the retina, There are different types of cells. The main ones are rods and cones. Rods work in dim light and give us black-and-white vision. Cones work in bright sunlight and help us see colors and details.

There are special cells called photoreceptors that turn light into messages for your brain. These messages travel through the optic nerve to your brain, where they become the pictures you see.

If something happens to your retina, like damage or if it is missing, your eye can still take in light, but your brain won’t get all the information it needs to make clear pictures.

The retina is like the screen of a camera that captures images and sends them to our brain for us to see.

Fovea Centralis

The fovea centralis is like the high-definition center of our eye, located right in the middle of the back of the eye.

There are two areas around the fovea: the parafovea and the perifovea, which are packed with special cells called cones and rods.

The parafovea is like a middle zone with lots of cones that help us see things sharply and clearly. This tiny spot, only about the size of a pinhead, is where our vision is the sharpest.

Unlike the fovea, which is all about clear vision, the rest of our eye has more of these cells called rods. Rods are like the night vision of our eye—they help us see in low light. They are especially handy for picking up faint objects in the dark.

When we want to see something really well, like reading a book or looking at a picture, our eyes move so that the thing we are looking at lands right on the fovea.

Optic Nerve

The optic nerve is like a cable that carries visual information from your eyes to your brain. It starts at the back of your eye, where the retina is, and travels to your brain.

Unlike other nerves in your body, it is wrapped in layers of tissue called meninges instead of the usual nerve coverings.

It is part of the central nervous system, not the peripheral nervous system, because it comes from a different part of the brain during development.

The optic nerve has around 770,000 to 1.7 million tiny nerve fibers, depending on the person. These fibers connect to cells in your retina, with some connecting to only a few cells for detailed vision and others to thousands for broader vision.

After leaving the eye, the optic nerve travels toward the brain through a small hole called the optic canal. Along the way, some fibers cross over at a spot called the optic chiasm, while others keep going straight back. 

These fibers mostly end up in a brain area called the lateral geniculate nucleus. From there, the visual information is sent to the visual cortex to be processed.

Some fibers also go to other parts of the brain that control things like reflexive eye movements and regulating sleep-wake cycles.

Sclera

The sclera, known as the white of the eye, is a tough outer layer made of collagen and elastic fibers. It is derived from the embryo’s neural crest. In kids, it is thin and slightly blue; in older people, it can appear yellow due to fatty deposits.

Dark-skinned individuals may naturally have darker sclerae due to melanin. The sclera covers most of the eyeball’s outer layer, connecting with the cornea and dura mater.

It helps maintain eye shape, resist forces, and attach extraocular muscles. Blood vessels mainly run on the surface and, along with the conjunctiva, can make the inflamed eye red.

Human eyes stand out because the sclera is easily visible, partly due to the smaller iris.

Choroid

The choroid is like a thin, pigmented layer in the eye sandwiched between the tough outer part (sclera) and the inner part (retina).

It has five layers, with the innermost one called Bruch’s membrane, which feeds the retina with oxygen and nutrients.

Next to Bruch’s membrane is the choriocapillaris, which is made up of tiny blood vessels that supply the retina and help clear away waste while also keeping the eye temperature in check.

Then, there are two layers of blood vessels (Haller’s and Sattler’s) surrounded by a mix of fibers, cells, and melanocytes, providing structural support to the choroid.

The outermost layer, called the suprachoroidea, sits between the choroid and the tough outer part of the eye (sclera). It helps drain fluid from the eye and maintain its pressure.

Blood gets to the choroid through some arteries and leaves through veins. The nerves make sure everything’s working fine, helping with blood flow and eye pressure.

Overall, the choroid’s main job is to keep the retina healthy by supplying it with what it needs. It also helps with eye temperature, pressure, and fluid drainage.

Aqueous Humor

Humor in your eye is a transparent fluid that helps keep your eye healthy. There are two types: aqueous humor and vitreous humor.

Aqueous humor is like a nourishing drink for your eye. It keeps your eye inflated and provides nutrients. It flows in and out, maintaining the right pressure inside your eye.

Your eye has two chambers: the anterior chamber (between the lens and cornea) and the posterior chamber (between the lens and iris).

In the posterior chamber, a part called the ciliary body makes aqueous humor. This fluid moves through your pupil to the front of your eye and then drains out into your bloodstream.

Vitreous Humor

The vitreous humor is like a clear gel inside your eye, between the lens and retina. It keeps your eye’s shape intact and feeds nutrients to nearby tissues. It sticks to the retina, helping light pass through for vision.

In forensic science, it is useful for finding foreign substances in a dead body because it is well protected and makes up most of the eye’s volume. Even though it is like gel, it is clear, so light can still pass through.

Apart from its support role, the vitreous humor contains various things like salts, sugars, proteins, collagen, and water. It also has special cells called phagocytes that keep the eye clean.

Conjunctiva

The conjunctiva is a thin, clear membrane that covers the inside of your eyelids and the white part of your eye. It helps protect your eye by creating a mucus layer in your tears.

This layer lubricates your eye and acts as a barrier against irritants. Working with your lacrimal and meibomian glands helps make tears, combining watery liquid, mucus, and oil.

It is like a protection for your eye, keeping it safe and moist. Problems with the conjunctiva can lead to dry eyes or infections.

Eyelids

An eyelid is like a thin skin cover for your eye, keeping it safe and moist. When you open your eye, it is the levator palpebrae superioris muscle that pulls the eyelid up.

The main job of eyelids is to spread tears and other liquids over your eye to keep it wet. It helps your cornea, the front part of your eye, stay healthy. Eyelids also stop your eyes from drying out when you are sleeping.

The blink reflex protects your eyes from stuff like dust. Plus, you’ve got those little hairs called lashes on your eyelids that help keep dirt away from your eyes. The way our eyelids look can be different in different groups of people.

Lacrimal Gland

The lacrimal glands are like tear factories for our eyes. They sit near the top and outer sides of our eye sockets. When they get inflamed, it is called dacryoadenitis.

These glands produce tears, which then travel across our eyes and eventually drain into our noses. There are two parts to the gland: one closer to the eye and one deeper inside the eye socket.

The part closer to the eye is called the palpebral lobe, and you can see it if you turn your upper eyelid inside out. The deeper part is the orbital lobe, which connects to the palpebral lobe with small tubes.

These glands release tears through ducts that lead to small holes in the inner corner of our eyelids. From there, tears travel through canals and eventually end up in our noses.

Eyelashes

Eyelashes are the hairs on our eyelids that help protect our eyes by catching debris and triggering the blink reflex when something gets too close.

They are super sensitive, with lots of nerve endings, helping us sense even light touches. Apart from guarding our eyes, they also keep the tear film intact, preventing excessive evaporation. Plus, they are a big part of what makes eyes attractive!

Meibomian Glands

Meibomian glands are like tiny oil factories located along the edges of our eyelids. They make an oily substance called meibum, which stops tears from drying up too quickly. It keeps our eyes moist and comfortable.

Meibomian glands keep tears where they are supposed to be, preventing them from spilling onto our cheeks. When we blink, the oily edge helps trap tears against our eyeballs and seals our eyelids tight.

Usually, we have about 25 of these glands on the top eyelid and 20 on the bottom. However, if these glands aren’t working right, it can lead to dry eyes and a condition called posterior blepharitis.

Optic Disc

The optic disc, also called the optic nerve head, is where nerves leave the eye. It is like an exit door for nerve fibers. This spot doesn’t have light-sensitive cells, so it creates a tiny blind spot in each eye. About 1–1.2 million nerve fibers leave through here in a typical human eye.

This area is where major blood vessels enter and exit the eye. It is located about 3 to 4 mm to the side of the center of vision. It is oval-shaped and usually around 1.76mm wide by 1.92mm tall.

Inside this spot, there’s a small dent called the optic cup. Its size and shape can vary, which is important for diagnosing certain eye diseases.

Optic Chiasm

The optic chiasm is like a traffic hub for visual messages in your brain. It is located near the pituitary gland at the base of your brain.

Its job is to take information from the optic nerves and send it to the optic tracts, helping with vision.

One cool thing about the optic chiasm is that some fibers from each eye cross over here. It means that what your right eye sees on the left side and vice versa gets swapped.

This swapping ensures that all the stuff you see on your right side goes to the left part of your brain, and what’s on your left side goes to the right part of your brain. It helps your brain process what you see correctly.

The optic chiasm receives blood supply from different arteries in your brain, which keeps it healthy and functioning well.

Optic Tract

The optic tract is like a pathway in your brain for visual information. It carries messages from your eyes to different brain areas.

Think of it as two separate roads—one for each eye. These roads bring in information from the left and right sides of what you see.

Each road is made up of fibers from different parts of your eyes. One part of the tract carries information from the outer side of your vision. In contrast, the other holds information from the inner side.

So, when you see something, the optic tract helps your brain understand what’s on your left and right sides. It is like the brain’s communication route for vision!

Macula

The macula is a crucial part of your eye that helps you see things directly in front of you, like small details. It is like the central hub of your retina, which is at the back of your eyeball.

When light enters your eye, it hits the retina, where cells called photoreceptors turn it into electrical signals. These signals travel to your brain through the optic nerve, creating the images you see.

The macula specializes in processing this information, allowing you to focus on specific aspects of what you are looking at.

Think of your whole retina as processing information like a spray from a garden hose, while the macula is like an eye dropper focusing on specific details.

If your macula is damaged, your vision can become blurry and lack detail, even though your eye still takes in light.

Anterior Chamber

The front part of the eye has a space filled with fluid called the anterior chamber (AC). It sits between the colored part of the eye (iris) and the inner surface of the clear covering (cornea). Three main problems can happen in this area: hyphema, anterior uveitis, and glaucoma.

• Hyphema: This is when blood fills up the anterior chamber because of bleeding, often due to a hit to the eye. It is like having blood in your eye.
• Anterior Uveitis: This is when there’s inflammation in the iris and ciliary body. It can cause redness and pain in the eye because of the swelling.
• Glaucoma: In this condition, there’s a blockage that stops the fluid from draining out of the eye properly. It leads to pressure building up inside the eye, which can damage the optic nerve and cause vision loss over time.

The depth of the anterior chamber can vary between 1.5 and 4.0 millimeters, with an average of 3.0 millimeters. As people age or if they are farsighted, the chamber might become shallower.

When it goes below 2.5 millimeters, there’s a higher risk of developing a type of glaucoma called angle-closure glaucoma.

Posterior Chamber

The posterior chamber is a narrow space behind the colored part of the eye (iris) and in front of the lens support structure. It is crucial for making and circulating the fluid that nourishes the eye.

Sometimes, a mature cataract or an artificial lens placed after cataract surgery can block the flow of this fluid. It led to a problem called the Iris bombe.

The posterior chamber causes pressure to build up in the posterior chamber, which can push the iris forward and block the drainage system of the eye. It leads to a type of glaucoma.

Suspensory Ligament

The suspensory ligament of the eyeball is also known as Lockwood’s ligament. It acts like a hammock under the eye. It stretches between two points on the sides of the eye and holds up the muscles below it.

This ligament is like a thickening in a protective layer around the eye. Its job is to keep the eye in its proper place in the eye socket and stop it from moving downward.

Canal of Schlemm (Scleral Venous Sinus)

Schlemm’s canal is like a drainage system for the eye. It sits in a circular canal at the back of where the cornea meets the white part of the eye. A few key parts shape this canal:

• Internal Scleral Sulcus: Think of it like a shallow groove along the circle where the cornea and sclera meet.
• Scleral Spur: This is a bump sticking out from the inner part of the groove. It is like a triangle with its base attached to the groove and its tip pointing inside the eye.
• Trabecular Meshwork: It is a network of tissue stretching from the tip of the bump (scleral spur) to the outer edge of the cornea.

Schlemm’s canal, which collects fluid from the front of the eye, is nestled in this space formed by these parts. It is lined with special cells called endothelial cells. These cells help with fluid drainage from the eye.

Lateral Geniculate Nucleus

The lateral geniculate nucleus (LGN) is like a relay station in the brain for vision. It is small and oval, sitting at the bottom part of the thalamus. There’s one on each side of the brain.

It is like a middleman between your eyes and your brain. It gets signals from the optic nerve coming from your eyes. Inside the LGN, there are layers of cells. These layers help sort out the visual information.

Then, the LGN sends these sorted signals to the primary visual cortex, which is the main processing center for vision in your brain. LGN also gets feedback from the visual cortex.

So, the LGN is crucial for processing what you see and passing that information along to the right parts of your brain.

Tenon’s Capsule

Tenon’s capsule is like a thin covering around the eyeball, stretching from the optic nerve to the cornea’s edge. It keeps the eyeball separate from the fatty tissue around it and helps it move smoothly.

Inside, a gap separates it from the eye’s outer layer by a space for lymph fluid. This fluid space connects to areas around the brain.

The capsule has holes at the back for blood vessels and nerves. It joins with the optic nerve’s covering and the eye’s outer layer.

At the front, it sticks to the conjunctiva, which covers the eye’s surface. Both Tenon’s capsule and the conjunctiva are linked to the eye’s center region.

Fornix

The fornix of the eye is like a stretchy connection between the inner surface of the eyelids and the eyeball. There are two fornixes in each eye: one on top and one on the bottom.

This connection lets the eyelids move smoothly. The fornix is made of three sides of tissue that attach to the eyeball and a flexible fold on the fourth side.

This setup lets the eyelids and eyeballs move without getting in each other’s way. The fornix is a protective layer that’s about 3 to 5 layers thick.

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External Sources-

• Wikipedia
• KenHub
• Optometrists
• Cleveland Clinic
• American Academy of Ophthalmology