Guide to Your Eye's Anatomy

The Outside of Your Eyes

 

Eyelid

Description:

Your eyelid is a very thin fold of skin, with a row of eyelashes.  It is supported by a strong tarsal plate (which gives your eyelids their shape).  The eyelid also has a layer of muscle that controls the opening and closing.

Function:

The eyelids play an important part in protecting your eyes. The strong reflex of your eyelids helps protect against any foreign bodies, such as dust, entering your eyes.

Regular blinking of the eyelids helps to spread tears around your eyes, keeping the surface of your eyes moist, for clear and comfortable vision.

Sclera

Description:

This is the white part of your eye.

Function:

The sclera is made of a tough tissue, which helps to protect the structure of your eyes, as well as providing support to the inside of your eyes.

Conjunctiva

Description: This is a mucus membrane that covers the front of your eyeball.  It is a lining which covers the white of your eye and has oxygen supplied by tiny blood vessels.

Function:

The conjunctiva is important as it acts as a seal, preventing objects like your eyelashes and your contact lenses from moving behind your eyeball.  It also helps spread your tears over your eyes.

Pupil

Description:  The pupil is simply a hole in the iris.  It’s the small black hole found in the centre of your eyes.

Function:

The pupil allows light to enter your eyes and pass onto the retina.  The muscles surrounding the pupil allow it to change size automatically depending on the light levels.  The pupil gets larger in the dark, to stimulate the peripheral retina, allowing you to see more clearly, and on bright, sunny days the pupil gets smaller to reduce the amount of harmful rays entering the eyes.

Iris

Description:  The iris is the coloured part of your eye.  It is a flat structure found behind the cornea.  The iris is made up of tiny pigment cells called the melanin.  The colour of your eyes, is determined by how much pigment is present in your iris.

People with brown eyes have the largest amount of pigment cells, which is the reason most fair-skinned people have blue eyes due to the smaller amount of pigment in their skin.

Function: The iris has a ring of muscular tissue, which allows it to alter the size of the pupil.  It also acts as a wall separating the front and back of your eyes.

Cornea

Description: The cornea is the transparent layer that covers the coloured part of your eyes, which includes the iris, pupil and anterior chamber (the space between the cornea and the iris).  It has no blood vessel supply, but it does have a number of nerves.  Hence why it is a very sensitive part of your eyes.

Function: The cornea has many important roles.  One of which is to help focus incoming light onto the retina.  Also, the high intensity of nerve fibres help to detect any foreign bodies entering your eye, which makes you blink repeatedly to wash out the particles.

Tear Duct

Description: This is found in the corner of your eyes closest to your nose.

Function: Any excess tears are taken away from the surface of your eyes through your tear duct known as the puncta.  This is why, when you are suffering from watery eyes, from either crying or any allergies, your nose runs, and sometimes you can taste the salt from your tears.

Lacrimal Gland

Description:  The lacrimal gland is located under the upper eyelid.

Function :  To produce tears which cover the surface of your eyes.

The Inside of Your Eyes

Crystalline Lens

Description: The crystalline lens is a transparent structure located behind your iris and pupil.  The lens is held in place by lots of fibres, like strings attached to a puppet, which in turn are attached to a muscle.

Function: The crystalline lens bends the light onto the retina and works in tandem with the lens changing shape, which allows you to focus at different distances.  The process of the lens changing shape is called accommodation.

Vitreous

Description: The vitreous is a transparent gel that fills the chamber between your lens and retina.

Function: The main function of the vitreous is to keep the eyeball in shape and maintain the general structure of your eyes.

Retina

Description: The retina is the light sensitive layer consisting of several layers and it lines the inner part of your eyes.  The retina has millions of light sensitive receptors called rods and cones.

Functions:  The receptors on the retina transmit electrical signals via the optic nerve to the brain to create the picture we see.

Macula

Description:  The macula is located in the centre of the retina, in the back of your eyes.  It also contains the fovea, which is a small depression or pit on the centre of the macula.

The macula has the highest amount of photoreceptors compared to the rest of the retina.

Function:  The macula is responsible in giving you your detailed central vision.  The macula allows you to see detail like the text on your television, reading and ability recognise faces, whilst the fovea provides you with the sharpest point of vision.

Optic Disc

Description: The optic disc normally looks creamy-white and oval in shape, and it’s the area where the optic nerve enters the eye.   It is very close to the macula.

Your optic disc has no photoreceptors located on its surface.  This is the reason you have a blind spot in each eye.

Function: The optic disc is where all the visual information received on the retina begins its journey away from the eye to the optic nerve.

Optic Nerve

Description:  The optic nerve connects your eye to the brain.  It’s like the optic nerve is the electrical wire plugged into the brain.

Function: The light formed on your retina is converted to electrical impulses, which pass along the nerve fibres from your optic disc to your brain.   Your brain then converts that into the visual image you see.

Central Retinal Vein and Artery

Description:  Your central retinal vein and artery are found on the back of your eyes along the retinal wall.

Function: Your retina requires a high amount of oxygen to function.  Your central retinal artery supplies blood to the retina. Its counterpart, the central retinal vein, then carries this away from the retina.