12.2

Choroid

Absorbs stray light rays that are not detected by photoreceptors. Contains blood vessels that nourish the eye.

Astigmatism

An uneven curvature of part of the cornea. Because its asymmetrical it cannot bend light rays so that they meet the correct focal point.

Cataracts

As the eye ages, protein structures degenerate. Making it opaque and preventing the light from passing through it. This can cause grey-spots on the lens.

Ciliary Muscles

Behind the iris, the choroid thickens to form this. It attaches to the lens, to focus images on the retina.

Colour Blindness

Caused by a lack or deficiency in a certain type of cones, usually red and green cones. Affect men more frequently.

Fovea Centralis

Contains high density of cones, provides acute vision. Located at the back and centre of the retina.

Iris

Donut-shaped, coloured.

Sclera

External layer of eye, white, tough and fibrous protective layer.

Hyperopia

Farsighted. Eyeballs are too short, so the image is focused BEHIND the retina. Convex lenses are needed.

Lens

Focuses light rays onto the Fovea Centralis. Flexible and changes shape.

Glaucoma

If the small ducts become plugged, pressure builds up in the eye, causing the blood vessels to rupture. This causes the cells to deteriorate due to lack of oxygen as nutrients.

Aqueous Humour

In front of the lens, within the anterior chamber. A clear, watery fluid that maintains the shape of the cornea, and provides oxygen and nutrients for the surrounding cells. Small amounts are produced everyday and drained by small ducts.

Cornea

Light enters the eye through. The transparent part in front of the eye

Pupil

Light enters the inner eye through here. Central dark part of the iris. Size adjusted based on light conditions.

Myopia

Nearsighted. Cannot see objects clearly if they're far away. Eyeball is longer than normal, so the light falls IN FRONT of the retina. Must wear concave lenses.

Cones

Sensitive to different colours. Packed most densely at the back of the eye.

Rods

Sensitive to light intensity.

Accomodation

The ability of the lens to change shape in order to focus images clearly on the retina. A reflex.

Retina

The internal, thin layer of the eye. Contains photoreceptors - rods and cones.

Vitreous Humour

The posterior chamber, surrounded by the retina. Clear, jelly-like fluid. Helps maintain shape of the eyeball, and it supports surrounding cells.

Adaptation

The process of the readjustment of the pupil and iris.

Optic Nerve

Transmits sensory impulses from the rods and cones to the brain.

Blind Spot

Where the ganglion cells merge to form the optic nerve. This area does not contain photoreceptors, and therefore cannot detect light.