Human eye: glossary of terms

The eye

The organ responsible for the visual system. Our eyes detect light and convert it into electrical impulses that make their way to the brain, where they become information.

Focus

The process by which the cornea and crystalline lens bend in order to absorb and process light reflecting on things at various distances.

Aqueous humour

The clear, watery fluid in the front of the eyeball, which is made up of water, sugars and various nutrients. It nourishes the cornea and the lens and gives the eye its shape.

Cone cells

Also referred to as cones, these cells can be found in the retina, and are responsible for colour vision and eye colour sensitivity.

Conjunctiva

A clear, thin transparent layer of tissue that covers part of the front surface of the eye and the inner surface of the eyelids.

Cornea

The clear, dome-shaped front part of the eye that helps your eye focus light, allowing you to see clearly.

Crystalline lens

The transparent, elastic structure inside the eye that bends to focus light rays onto the retina.

Fovea

The central part of the macula, necessary for activities where visual detail is important, such as driving or reading.

Iris

The coloured part of the eye surrounding the pupil that controls the amount of light that enters into the eye.

Macula

The central part of the retina that allows us to see fine details.

Optic disc

A disc on the retina that's the point of entry into the optic nerve. It lacks visual receptors, so it's also known as the blind spot.

Optic nerve

A bundle of nerve fibres that connect the retina with the brain and helps us interpret what we see.

Pupil

The opening in the centre of the iris that lets light pass through to the back of the eye.

Retina

The light-sensitive nerve layer that lines the inside of the back of the eye. It creates electrical signals that travel through the optic nerve to the brain.

Rod cells

Positioned on the outer edges of the retina, these cells, or rods, are used in peripheral vision, and help you detect motion in the dark.

Sclera

The dense protective tissue of the eyeball that forms the 'white' of your eye. Sclera forms over 80% of the surface area of the eyeball, from the cornea to the optic nerve.

Vitreous humour

A clear gel-like substance that occupies the space between the crystalline lens and the retina and transmits initial light waves.

Anterior chamber

Positioned behind the cornea, in front of the lens and iris, this chamber contains the aqueous humour, allowing it to drain from your eyes into your bloodstream.

Choroid

Sitting between the eye's sclera and the retina, this small, vascular layer supplies the outer layer of the retina with oxygen and nutrients. This part of the eye is responsible for the red-eye effect in photographs.

Ciliary body

Situated between the choroid and iris, this circular structure produces the aqueous humour while keeping the lens in the correct position.

Trabecular meshwork

Set at the base of the cornea, this area of tissue drains the aqueous humour from the eye through the anterior chamber, using tubes known as Schlemm's canal.

Amblyopia (lazy eye)

A condition that usually develops in childhood where one eye sees better than the other, and the weaker eye, the 'lazy eye', wanders inwards or outwards.

Astigmatism

A prevalent and minor condition that means the eye doesn't focus light evenly on the retina, making your vision appear unclear at any distance. Contact lenses for those with astigmatism often include the word 'toric' or 'astigmatism' in their name.

Cataract

This condition is caused when the eye's internal lens is clouded, resulting in blurred vision.

Conjunctivitis (pinkeye)

A swelling and infection of the conjunctiva and common causes for this include viruses, bacterial infections and allergies.

Diplopia (double vision)

A condition where you see two images of a single object, often as a result of diseases, previous trauma or a stroke.

Dry eye

If the eyes can't produce enough tears, this leads to a common condition that causes your eyes to appear red and feel uncomfortable. Ageing and medical problems are known to create this condition.

Hyperopia (farsightedness)

A common refractive error that occurs when your eyeball is shorter than normal or your cornea is curved too little, resulting in distant objects looking clear, but close objects appearing more blurred. Contact lenses for this prescription require a plus/+ power.

Myopia (nearsightedness)

A common vision condition caused by an incorrectly-shaped eyeball or cornea, in which you can clearly see objects that are close to you, but objects in the distance appear blurry. Contact lenses for this prescription require a minus/-power.

Presbyopia

An age-related condition of long-sightedness that is caused by the loss of elasticity of the lens in the eye, which normally occurs during middle and old age. Contact lenses for presbyopia visual correction often include the word 'multifocal', 'progressive', 'bifocal' or 'presbyopia'.

Retinal detachment

An eye problem that occurs when the retina begins to pull away from the blood vessels that give it oxygen. Urgent surgical repair is needed, and diabetes and trauma are common causes.

Cataract surgery

An operation where the cloudy cataract is removed and the natural lens is replaced with a man-made version.

Gas permeable contact lenses

These durable lenses are more rigid in design, and unlike soft lenses don't contain any water, but are still comfortable and can be worn for longer periods.

Hydrogel/silicone hydrogel contact lenses

Similar to standard hydrogel soft lenses, silicone hydrogel lenses are made of a plastic material, which goes hard when it has dried out but which actively absorbs water to become soft and pliable again. Silicone hydrogel lenses enable up to five times more oxygen to reach the cornea than regular hydrogel lenses.

Photorefractive keratectomy (PRK)

This type of laser surgery involves the removal of the surface cells of your cornea to improve vision problems.

Laser photocoagulation

The laser is used on parts of the retina that have poor circulation or to remedy abnormal blood vessels.

LASIK (laser-assisted in-situ keratomileusis)

A procedure that involves creating a thin flap in your cornea, and using a laser to reshape it - a popular solution for astigmatism, myopia and hyperopia.

Soft contact lenses

Made from flexible and soft plastic material (hydrogel or silicone hydrogel), these contact lenses allow oxygen to pass through the cornea with ease, and are comfortable and easy to apply.