The Mechanisms of the Human Eye

Our eyes are one of the body’s most remarkable and important parts. Not only do they give us one of our five senses – sight – our eyes are one of the few parts of our body that can’t be replaced. So it’s really important to look after them as we only have one pair to last a lifetime.

This week is National Eye Health Week (24-30 September) which aims to raise awareness of eye health and encourage people to have regular eye tests. So we thought now would be the perfect opportunity to look at the mechanisms of the human eye.

AQUEOUS HUMOUR – this is a clear fluid that fills the space between the lens and the cornea. The fluid continuously nourishes the iris, lens and cornea and stabilizes the intraocular pressure.

CORNEA – the clear, covering of the eyeball that allows light to travel into the eye.

IRIS – this is the coloured part of the eye found at the front of the eye, with the lens behind it. The iris controls the size of the pupil, and therefore the amount of light allowed to pass through to the retina.

PUPIL – the black opening in the middle of the iris that allows light to pass to the retina.

LENS – this is the transparent disc held behind the pupil which focuses light onto the retina.

RETINA – light sensitive cells which respond to light and send signals to the brain via the optic nerve. This is the inner most layer of the inner eye.

MACULA – a small central are of the retina which controls the ability to see straight ahead and fine detail.

FOVEA – found in the centre of the macula, the fovea provides the clearest, most detailed vision.

OPTIC NERVE – the bundle of nerve fibres which relay messages between the eye and the brain.

VITEOUS – the gelatinous mass that fills the back of the eye and helps to keep the shape between the lens and the retina.

SCLERA – this is the tough, protective outer layer covering most of the eyeball. This layer is the white layer of the eye.

All of these separate components of the eye work together to give us the ability to see.

When light travels into the eye through the cornea, the pupil contracts or dilates to control the amount of light passing into the eye and the image is partially focused as it passes through the aqueous humour and onward through the lens towards the retina. The lens changes shape to further focus and create a sharp point on the retina, once the light has travelled through the vitreous humour. The retina receives the light images and transfers them into electro-chemical signals by the photoreceptors. This is then sent to the brain via the optical nerve where it is translated to create sight.

When all the parts of the eye and the visual centre of the brain are working efficiently and communicate with each other, we experience sight. However sometimes this can go wrong, either through disease, trauma or hereditary conditions. A lot of eye conditions, if detected at an early stage, are treatable or manageable. So it’s vitality important to have regular eye examinations. When we carry out an eye examination, we don’t just check the patient’s prescription, we perform a thorough examination, looking at the complete health of the eye both externally and internally.

One the instruments we use during an eye examination is the retinal camera, which in a nutshell takes a digital image of the back of the eye and in particular the retina. This procedure is simple, painless and non-invasive and allows us to quickly diagnose a number of common eye conditions, such as glaucoma, diabetes, age related macular degeneration and choroidal nevus. The images we take are stored, so over time we can build an invaluable record of your eyes and monitor any changes found.

6 Fascinating Facts About the Human Eye