4.4 Lenses & The Eye

Accommodation

The ability of the lens of the eye to change its shape to adjust its focus

Cornea

a transparent a transparent covering over the iris of the eye; it bends light into the lens

Real image

an image formed when rays of light do actually meet (real, inverted)

Virtual image

an image formed when rays of light do not meet (virtual, upright)

Ciliary body

attached to the lens, the muscles in the ciliary body change the shape of the lens; changes the focal point

Vitreous humor

clear fluid between the lens and the retina

Eye muscles

enables the eye to rotate in its socket

Dilator muscle

enlarges the pupil, allowing more light into the eye.

Rod cells

found in the retina- at the back of the eye. These cells are receptive to dim light and movement

Choroid

has a rich blood supply and nourishes retina

Lens

in the eye it is a flexible structure that enables light to be focused on the retina

Sphincter muscle

makes the pupil smaller, which stops light entering the eye

Cone cells

more concentrated in the fovea centralis-the area of sharpest vision. These cells are receptive to colour

Retina

nerve tissue at the back of the eye, consisting of cone cells and rod cells; light is converted into an electrical signal here

Optic nerve

a nerve that carries an electrical signal from the retina to the brain

Concave lens

a lens that curves inwards on both sides

Conjunctiva

A membrane that covers the sclera

Fovea centralis

Responsible for sharp central vision

Sclera

The white part of the eye

Convex lens

a lens that bulges outwards on both sides

Focal length

the distance from a lens to its focus

Hyperopia

the inability to focus on close objects because the lens in too long

Myopia

the inability to focus on distant objects because the lens is too small

Aqueous humor

watery fluid produced by the ciliary body to lubricate the lens and cornea