The eye

Structure and how it works

What is the eye?

The eye is a part of the body. It is a vital part as it gives us one of the five senses which is to see which is really important in today's life.

Parts of the eye and Structure of the eye

Cornea

The cornea is the outermost layer of the eye and is primarily responsible for focusing the light that comes into our eyes. There are 5 layers to the cornea. The outer layer acts as a kind of shield to the elements and can usually repair itself within a few days of suffering a minor injury. The deeper layers exist mainly to strengthen the eye.

Pupil

The pupil is the black circle in the center of the eye, and its primary function is to monitor the amount of light that comes into the eye. When there is a lot of light, the pupil contracts to keep the light from overwhelming the eye. When there is very little light, the pupil expands so it can soak up as much as possible.

Iris

The iris is the colored part of the eye. Although it might seem purely fake, the iris actually functions to adjust the size of the pupil. It has muscles that contract or expand depending on the amount of light the pupil needs to process images.

Lens

The lens exists behind the pupil and is responsible for allowing your eyes to focus on small details like words in a book. The lens is in a constant state of adjustment as it becomes thinner or thicker to accommodate the detailed input it receives. With age, the lens loses a lot of its elasticity which often results in cataracts and presbyopia because the lens cannot adjust as well to its surroundings as it used to.

Vitreous Humour

The vitreous humour is a gel-like substance that helps to keep the eyeball in its proper, circular shape. This is the area in the eye where floaters develop as pieces of the vitreous humor clump together and cast shadows onto the retina. With age, the vitreous humor begins to shrink and can cause problems like posterior retinal detachment or retinal tears.

Retina

The retina is the area at the back of the eye that receives the refined, visual message from the front of the eye, and it transmits that visual message to the brain using electrical signals.

Sclera

The sclera is the white part of the eye, and its main function is to provide strength, structure, and protection for the eye. The sclera contains blood vessels that can tell an eye doctor a lot about the state of your overall health.

Optic Nerve

The optic nerve is located in the back of the eye. The job of the optic nerve is to transfer visual information from the eye to the vision centers of the brain via electrical impulses.

Macula

The Macula is a small,sensitive area in the middle of the retina, it is responsible for central vision.It is used for all detailed visual tasks.

Suspensory Ligament

The suspensory Ligaments in the eye are ligaments, which support the lens to hold it in place. They are attached to the ciliary body and the lens.

Aqueous Humour

The aqueous humour is a clear watery fluid, which is found in the space between the cornea and the lens. It supplies nutrients to the front section of the eye and provides the presssure to maintain the convex shape of the cornea.

How it Works?

Light from the sun, or an artificial light, travels in a straight line, bounces off objects and into our eyes through the pupil. Depending on the amount of light, the iris changes the size of the pupil to let more or less light in. This is to prevent damage to the eyes, by stopping too much light entering the eye when it is bright, and maximising the amount of light entering the eye when it’s dark.The light then passes though the lens. The lens focuses the light onto the back surface of the eye, the retina. Depending on how far away the object is, our lens needs to change shape to keep the light focussed on the retina. A fatter lens bends light more than a flatter lens. The human eye changes the shape of the lens as we look at far or near objects to keep them in focus. This is called accommodation. When we look at a far object, the light does not need to bend a lot to converge on the retina, so the suspensory ligaments pull on the lens to make it flat. When we look at a near object, the light has to bend more to converge on the retina, so the suspensory ligaments pull less, allowing the lens to spring back into a fatter shape.After receiving focussed light, the retina transforms this into an electrical impulse, which travels to the brain via the optic nerve. The image we receive on the retina is actually upside-down – our brains turn the image around so we don’t get confused!
A Journey Through the Human Eye: How We See