This is a tough, fibrous outer coating which covers most of the eye (with small gaps at the very front and back). It protects the eye, contains the elements within and gives it its distinctive ball-like shape. Part of it is visible around the iris; we refer to it as the ‘white’ part of the eye.
This covers the gap in the sclera at the front of the eye. Like the sclera it is tough and protective. It is clear however, and bulges out from the rest of the eye, where it coats and protects the area around the iris, pupil and lens. It is a unique part of the body in that it is living tissue but does not rely on oxygen-giving blood vessels to live - it gains that from the oxygen that is dissolved in tear fluid.
This is the coloured part of the eye and sits behind the clear shell of the cornea. The colour is caused by the amount of pigment present in the eye. Large amounts of pigment leads to brown eyes, whilst those with less pigment will have blue eyes. Babies lack this pigment for a while after birth, which is why they always have blue eyes. As their eyes develop, they may gain more pigment to develop their eye colour. The iris is a muscle which can contract or constrict according to the amounts of light you find yourself in, controlling the size of the pupil.
The purpose of the pupil is to control the amount of light that enters the eye - either too much or too little can affect the clarity of your vision. Basically a hole into your eye - albeit covered by the clear cornea - it appears to be black as there is very little light in the area of the eye behind it. The iris controls the pupil size, which regulates the amount of light let into the eye. During the day your pupils will be smaller. But at night, or in darkness, your pupils will dilate, becoming large to allow your eyes to take in as much light possible to enable you to see as well as possible.
The Crystalline Lens
This is a naturally-occurring lens that sits directly behind your pupil, usually just referred to as ‘the lens’. It is made up of several clear layers that sit on top of one another, like the skin of an onion. This allows the lens to be pliable, meaning that its shape can be changed, which in turn allows it to correctly focus light that enters from the pupil and redirect it to the back of the eye. The shape of the lens is controlled by the ciliary body - muscles attached to the outer edge of the iris, and it constantly shifts to ensure that all light is correctly focused onto the right parts of your retina.
This is the space between the elements at the front of your eye and is filled with a clear fluid called aqueous humour for stability. This is secreted by the ciliary body.
This is the clear mucous membrane which covers the outside of your eye, coating the sclera and lining the inside of your eyelids. This protects the eye from outside particles such as dust and grit.
This covers almost the entire inside surface of the eye and is covered with millions of light-sensitive nerve cells, rather like the taste buds that sit along your tongue. There two main types of these cells, often referred to as ‘rods’ and ‘cones’ due to their shapes. There are more rods than cones - around 20 rods per cone - and these define how you see what you see. Cones are less sensitive to light but can distinguish between colours and details in bright light. Rods however, are more sensitive (so much so that they tend to shut down in bight light - ie in daytime) and thus are more effective to distinguish details in dim light (rods effectively control your natural ‘night vision’). These cells react to the light and create electrochemical signals which are then passed on to the optic nerve.
The Posterior (Vitreous) Chamber
This is the main space in the middle of the eye behind the lens. It is filled with a viscous, but clear, jelly-like substance called vitreous humour. This maintains the shape, and overall stability of the eyeball itself.
This is a small depression in the retina at the back of the eye, where the nerves and blood vessels enter the optic nerve. It covers a roughly circular area and is on average about 2.5mm in diameter. It forms a gap in the retina so there are no rods or cones in the area, so it is not sensitive to any light at all - it is commonly called the ‘blind spot’. This is basically the end of the optic nerve - the tube that links your eye to you brain. This carries the electrochemical impulses from the retina to the vision centre of your brain, completing the process of vision. What you can ‘see’ is a mental picture made up of information from these chemical impulses.