Why do parts of the eye need to be clear

The pupil, or black dot at the centre of the eye, is an opening through which light can enter the eye. The iris, or coloured part of the eye, surrounds the pupil. It controls how much light enters the eye by changing the size of the pupil. The cornea, a clear window at the front of the eye, covers the iris and the pupil.

A clear lens, located behind the pupil, acts like a camera lens by focusing light onto the retina at the back of the eye. The retina is a light-sensitive inner lining at the back of the eye.

Ten different layers of cells work together in the retina to detect light and turn it into electrical impulses. The retina Special cells called cones and rods are located in the retina. Cones The majority of the cones are located in the macula, or central area, of the retina. Rods The majority of the rods are located in the peripheral, or outer area, of the retina.

How the eye sees For people with normally functioning eyes, the following sequence takes place: Light reflects off the object we are looking at. Light rays enter the eye through the cornea at the front of the eye.

The light passes through a watery fluid aqueous humor , and enters the pupil to reach the lens. The lens can change in thickness to bend the light, which will focus it onto the retina at the back of the eye. On the way to the retina, the light passes through a thick, clear fluid called a vitreous humor. The vitreous humor fills the eyeball and helps maintain its round shape. The light then reaches the back of the eye and hits the retina. The retina translates the light into electrical impulses which are then carried to the brain by the optic nerve.

Finally, the visual cortex or centre of the brain interprets these impulses as what we see. What normal vision is like To understand the vision of someone with an eye condition, it can be helpful to know what normal vision is like.

It changes sizes to adjust for changes in light. The retina is the light-sensitive part of the eye. It has one major artery and one major vein, which is called the central retinal vein. Sometimes, branches of this vein can be blocked.

The uvea is the middle section of the eye. It has three parts: the iris the colored part of the eye , the ciliary body and the choroid. Inflammation or swelling of any of these parts or their adjacent tissues is called "uveitis. Graphic courtesy of National Eye Institute Cornea Like the glass on a watch, the cornea is the clear protective coating on the front of the eye that allows light to pass through it without distortion.

Conjunctiva The conjunctiva is the clear covering like cellophane of the white part of the eye, the sclera. Lacrimal System The lacrimal tear system is a miniature drainage network, which prevents tears from continuously rolling down the cheeks. Lens Every camera must have a lens to properly focus the picture. Macula The macula is a part of the eye that contains special light-sensitive cells which allows us to see fine details clearly.

Optic Nerve The optic nerve is the pathway that connects the eye to the brain. Orbit The orbit is the bony housing in which the eyeball sits. Pupil The dark center of the iris the colored part of the eye is the pupil. Retina The retina is the light-sensitive part of the eye. Sclera The sclera is the "white" part of the eye.

Pupil — this is the opening in the centre of the iris that lets in light. It is regulated by the iris. Retina — the light-sensitive tissue lining at the back of your eye that converts light into electrical impulses that are sent along the optical nerve to the brain.

Sclera — also known as the white of your eye, this is the outer layer of the human eye. Vitreous humour — a clear gel that fills the inside of the eye and helps it to retain its shape. Tears have three main components; a watery component, an oily component and mucus. These create a film which covers the white of the eye and the cornea. A problem with any of the three layers may cause dry eye. Necessary cookies are absolutely essential for the website to function properly.

The muscles that move the eyeball are attached to the sclera. Suspensory ligament of lens. A series of fibers that connects the ciliary body of the eye with the lens, holding it in place. Upper eyelid. Skin that covers the upper part of the eyeball, including the cornea, when closed.