EYE The eye is an extension of the brain

Eye brain proxomity Can you see : the optic nerve bundle? Spinal cord?

Cross section You must know the position of: Retina Lens Cornea Sclerotic Optic nerve Cilary muscles Suspensory ligaments

Cornea: The clear, strong surface layer of the eye covering the iris and pupil. The cornea is the first part of the eye that bends (or refracts) the light and provides most of the focusing power.

Conjunctiva: Is a membrane that covers the cornea and lines the inside of the eyelids. It helps lubricate the eye by producing mucus.

Sclera: Is the outside white of the eye which covers the entire eye apart from the front. It supports and protects the eye, serves as an attachment for the extrinsic eye muscles and aids in focusing.

Choroid: Is the second layer of the eye between the sclera and retina Choroid: Is the second layer of the eye between the sclera and retina. It serves as additional protection and support for the eye. It is the blood-rich membrane that is responsible for supplying blood to the retina

Retina: The retina is the inner lining of the back of the eye that contains the visual cells (rods and cones). The function of the retina and visual cells is to convert light rays into electrical impulses that are transmitted to the brain by way of the optic nerve

Iris: The coloured muscular membrane which lies behind the cornea and in front of the lens. Determines the size of the pupil and hence the amount of light entering the eye

Lens: A transparent biconvex disc made of protein Lens: A transparent biconvex disc made of protein. It focuses the light on the retina

Changing lens thickness The lens is slightly elastic, its relaxed state is short and fat. Cilary muscles are attached to the lens, when contracted they pull the lens thin

Aqueous humor: Fluid that fills the anterior cavity Aqueous humor: Fluid that fills the anterior cavity. It has small refractive power. Vitreous humor: Fluid that fills the posterior cavity. It has small refractive power.

Ciliary Body: Is the muscle that holds the lens in place yet allows for flexible movement of the lens. It separates the posterior and anterior cavities.

Optic Nerve: Is attached to the retina and transmits visual signals to the visual cortex of the brain for processing.

Fovea: the concave centre of the retina Fovea: the concave centre of the retina. The region of highest visual acuity and cone cell density

Retina – receives the image Full of light receptors which are sensitive to: Colour Light levels Massive blood supply is also needed Fovea is the main focal point and has greatest density of light receptors

Retina receptors Light receptors are called rods and cone

Focusing on objects The lens and cornea focus the light on the retina

Focusing The lens job is to make the rays hit the same point The red rays will be out of focus

Bending light Light is refracted and bent to focus it as it passes through the lens Lens thickness can be changed so the amount of bending is changed

Near vision to bend the light more to focus it Fat lens needed

Distance vision Rays enter the eye closer together Need less bending Thinner lens needed

Controlling light levels Your eye are very sensitive and can be damaged by harsh light. Your iris controls light allowed into the eye by changing the size of the pupil

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