Bio30 Chapter 12.2 - Photoreception

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Sclera

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

Cornea

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

Choroid

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

Iris

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

Pupil

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

Adaption

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

Retina

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

Rod

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

Cone

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

Glaucoma

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

Lens

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

Accommodation

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

Cataract

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

Astigmatism

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

Myopia

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

Hyperopia

Fair-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 detecing light

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