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The white, tough, fibrous protective layer that gives the eye its shape


The transparent part of the sclera at the front of the eye, through which light enters


Vascular membrane of the eye that lies between the retina and the sclera; absorbs stray light rays that are not detected by the photoreceptors in the retina


The doughnut-shaped, coloured muscle formed from the choroid at the front of the eye; adjusts the central dark pupil to regulate the amount of light that enters the eye


Aperture in the middle of the iris of the eye, whose size can be adjusted to control the amount of light entering the eye


In vision, the process by which the iris adjusts the size of the pupil based on the light conditions, thereby controlling amount of light that enters


The innermost layer of the eye, containing the photoreceptors (rods and cones)


Type of photoreceptor in the eye that is more sensitive to light intensity (level of brightness) than is a cone, but is unable to distinguish colour


The type of photoreceptor in the eye that is sensitve to different colours

Optic Nerve

A nerve that carries messages from the photorecepotors in the retina to the brain

Aqueous Humour

Clear, watery fluid in anterior chamber of eye; maintains the shape of the cornea and provides oxygen and nutrients for the surrounding cells, including those of the lens and cornea


Condition caused by blockage of the draining of aqueous humour in the eye; resulting pressure ruptures delicate blood vessles in the eye and causes deterioration of the cells due to a lack of oxygen and nutrients, can lead to blindness of untreated

Vitreous Humour

A clear, jelly-like fluid inside the posterior chamber of the eye; helps to maintain the shape of the eyeball and support the surrounding


Clear, flexible part of the eye that focuses images in the retina


In the eye, adjustment that the ciliary muscles make to the shape of the lens to focus on objects at varying distances


Cloudy, or opague, grey-white area on the lens of the eye caused by the degeneration of the protein structure of the lens; prevents the passing of light; increases in size over time and can lead to blindness if not medically treated


Uneven curvature of part of the cornea or lens that results in uneven focus and therefore blurry vision


Near-sightedness, or difficulty seeing things that are far away; caused by ciliary muscles that are too strong or an eyeball that is too long


Far-sightedness, or difficulty seeing things that are nearby; caused by weak ciliary muscles or an eyeball that is too short

Fovea Centralis

Concentration of cones on the retina; loacted directly behind the centre of the lens

Colour Blindness

An inherited condition that occurs more frequently in males than in females; is actually colour deficiency, caused by a lack of particular cones, usually red and green cones (thus, a red-green colour-blind person may find it difficuly or impossible to know the difference)

Blind Spot

Region of the retina lacking photoreceptors (rods or cones) and where the optic nerve leaves the eye; is incapable of detecting light

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