Skip to content

Parts of the human eye and their functions

The main organ of sight is the eye and, with it, we have access to one of the most complex human sensory-receptive systems . It is made up of several structures and in this article we are going to tell you which are the main ones.

What is the eye?

The eye is the organ that is responsible for detecting light and sending signals through the optic nerve to the brain. Its structure is very valuable because it captures images and gives us the ability to see. It allows us to perceive light, movement and gives us the ability to differentiate depth and colors.

Its viewing angle is 200 degrees and it can see ten million shades and colors . It is surrounded by some structures that protect it, such as the eyelashes, eyelids or eyebrows. The first two prevent foreign objects from entering it and the third prevents sweat from falling from your forehead.

Its shape is spherical and is divided into two sections filled with vitreous and aqueous humor . The anterior chamber is smaller, situated between the iris of the eye and the cornea, and the posterior chamber is made up of the rest of the parts of the eye.

Functions and parts of the eye

The eye works like a photo camera. The part of it called the crystalline adjusts depending on the distance of the stimulus and serves as a lens that facilitates the refraction of light. The pupil would be the diaphragm , that is, through it the image enters the eye to be projected on the retina. From there it is sent through the optic nerve to the brain.

The layers that make up the eye are:

  • Outer layer , formed by the scleral and corneal membranes.
  • Middle layer , where you will find the choroid, iris of the eye, ciliary body and lens.
  • Inner layer , formed by the retina and the aqueous and vitreous humors.

Next, we are going to see what each of these parts of the eye is for.


It is the part that is in contact with the outside and results in a transparent structure that covers the iris and lens. Aqueous humor and tears facilitate its proper functioning. It helps to focus visible objects because it allows the refraction of light.

The situations of astigmatism , pterygium, keratitis or keratoconus are related to it.


It is the white area of ​​the eyes , the outermost and hardest layer. It is a very fibrous layer that protects the internal components of the eye and contains collagen.

Its front part joins the cornea and the back part has an opening to allow the connection between the retina and the optic nerve.


The choroid membrane is a small vascular layer located between the retina of the eye and the sclera. Its main function is to provide oxygen and nutrients to the outer layers of the retina through blood vessels. But another of its functions is to keep the temperature in the eye constant.


This tissue is pigmented due to melanin that gives rise to the color of the eye and is formed by the stroma, which is a fibrovascular tissue. It is connected to a muscle that controls the dilation and constriction of the pupil and separates the posterior and anterior chambers of the eye.

It acts like a diaphragm and controls the amount of light that penetrates the organ . Their reaction to changes in light is not immediate, but it is very fast.


It is in charge of giving the eye the focus or power of refraction and is located behind the iris. It is a fibrous tissue with a shape that it can change to reduce or increase its power. This shape change allows you to focus on nearby images when it bulges and flattens to focus on those that are further away. The image on the retina is formed when light rays pass through the lens.

It delimits the posterior chamber, which contains the vitreous humor, from the anterior chamber, which contains the aqueous humor.


It is an opening in the iris, the black hole in the center of the iris. Regulates the amount of light that enters the eye . When the light is strong, the pupils are smaller and, when the light is dimmed, they dilate.

The pupil has a black color because the tissue absorbs a large part of the light that passes through it.

Aqueous humor

It is a transparent and light fluid, very similar to plasma. It is composed mostly (99.9%) of water. The other 0.1% are vitamins, proteins, essential nutrients and sugars. It is located between the lens and the cornea.

It is a very important liquid in eye health, since it not only nourishes the lens and cornea with the supply of glucose or amino acids, but is responsible for maintaining intraocular pressure , facilitates the expansion of the cornea and transports vitamin C in the frontal segment.

Vitreous humor

It is a clear, colorless liquid that fills the space between the retina and the lens. It has a gelatinous consistency and is composed mostly of water (99%). The rest is a mixture of sugars, salts, collagen, and proteins. It plays a fundamental role in protecting the eye and helps preserve its spherical shape , as well as helping the retina stay in place.

Its density is higher than that of aqueous humor, which is found in the anterior chamber. It constitutes most of the globe and its functions are to provide it with rigidity, maintain intraocular pressure, cushion possible impacts and fix the retina, as we have already pointed out.


This transparent, mucous membrane covers the sclera or ocular surface, as well as the inner part of the eyelids. It produces tears and mucus to lubricate the surface of the eyes and contributes to its disinfection, since it causes microorganisms to be out of it.


It is a sensory membrane that covers the entire back surface of the eyes. It is responsible for receiving the images and transforming them into nerve signals that, through the optic nerve, are transmitted to the brain.

The cells of the retina are made up of nervous tissue and are sensitive to light. In its central part you will find the fovea , which is an area with a high concentration of cones, which turn out to be responsible for perceiving both fine details and color. This is the area of ​​greatest visual acuity.

The other important part is the optic disc, which is the place where the axons that shape the cranial nerve come out.


It is the area of ​​the retina where the photoreceptors, rods and cones are located , and is responsible for central vision. It is what allows you to read or distinguish people’s faces.

Optic nerve

It is known as cranial nerve II or second cranial nerve, because it is the second of the XII cranial nerves. It is sensitive and is located in the back of the eye, in charge of transferring visual information through electrical impulses from the retina to the brain.

The images captured by the left eye reach the right hemisphere of the brain and those from the right eye reach the left hemisphere. Later, the brain will develop a definitive image.


This spherical structure contains all the sensory receptors that are specialized for vision. It houses the photoreceptors, the retina, the iris, the cornea, the lens, and all the structures necessary to focus light . It also contains the sclera, which covers four-fifths of the globe and has important functions for the muscles that are responsible for eye movement.

It is composed mostly of the vitreous humor, which is a transparent material in the form of a gel.

Photo receivers

They are the cells of the retina that respond to light. Its main purpose is to provide night vision and color vision. These cells are divided into two types: rods and cones.

  • Canes: they work at low light levels and are responsible for perceiving the shape, size and brightness of images. They do not perceive fine details or color. They are responsible for black and white vision.
  • Cones: they have a conical projection on the retina of the eye and are associated with the perception of fine details and color vision.

How does the human eye work?

When light hits the eye, the first thing it does is go through the cornea. Its shape is curved, which allows it to deflect the rays and allows the light to pass through the pupil and reach the lens.

The iris, which we have already said is the colored part of your eyes, is responsible for regulating the light that enters at all times and works closely with the ciliary muscles. All this means that the pupil can contract when the light is intense or dilate when the light intensity to which you are exposed is very low.

When light hits the curve of the lens, it is reflected and directed towards the retina. At this exact point is where the conversion of light into electrical energy occurs . Finally, the energy will circulate through the optic nerve to the brain stem, where it is definitively transformed into the image or images that you see, with the help of the occipital lobe.

Website | + posts

Hello Readers, I am Nikki Bella a Psychology student. I have always been concerned about human behavior and the mental processes that lead us to act and think the way we do. My collaboration as an editor in the psychology area of ​​Well Being Pole has allowed me to investigate further and expand my knowledge in the field of mental health; I have also acquired great knowledge about physical health and well-being, two fundamental bases that are directly related and are part of all mental health.

Leave a Reply

Your email address will not be published. Required fields are marked *