The eye WALT To identify the main parts of the eye and their functions To explain how light is focussed onto the retina

Eye, eye

EYE The eye is an extension of the brain

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

The eye

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

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

The Lens The crystalline lens is located just behind the iris. Its purpose is to focus light onto the retina.  The lens is encased in a capsular-like bag and suspended within the eye by tiny "guy wires" called zonules or suspensory ligaments.  

The Cornea The cornea is the transparent, dome-shaped window covering the front of the eye.  It is a powerful refracting surface, providing 2/3 of the eye's focusing power. 

The Sclera The sclera is commonly known as "the white of the eye."  It is the tough, opaque tissue that serves as the eye's protective outer coat.  Six tiny muscles connect to it around the eye and control the eye's movements.  The optic nerve is attached to the sclera at the very back of the eye. In children, the sclera is thinner and more translucent, allowing the underlying tissue to show through and giving it a bluish cast.  As we age, the sclera tends to become more yellow.

Ciliary Muscles One function of the ciliary body is the production of aqueous humor the clear fluid that fills the front of the eye.  It also controls accommodation by changing the shape of the crystalline lens.  When the ciliary body contracts, the suspensory ligaments relax.  This allows the lens to thicken, increasing the eye's ability to focus up close.  When looking at a distant object, the ciliary body relaxes, causing the zonules to contract.  The lens becomes thinner, adjusting the eye's focus for distance vision.  

The Optic Nerve The optic nerve transmits electrical impulses from the retina to the brain.    When examining the back of the eye, a portion of the optic nerve called the optic disc can be seen.   The retina's sensory receptor cells of retina are absent from the optic nerve.  Because of this, everyone has a normal blind spot.  This is not normally noticeable because the vision of both eyes overlaps

The Iris The colored part of the eye is called the iris.  It controls light levels inside the eye similar to the aperture on a camera.  The round opening in the center of the iris is called the pupil.  The iris is embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size.  

Aqueous Humor The aqueous is the thin, watery fluid that fills the space between the cornea and the iris (anterior chamber).  It is continually produced by the ciliary body, the part of the eye that lies just behind the iris.  This fluid nourishes the cornea and the lens and gives the front of the eye its form and shape.

Vitreous Humor The vitreous is a thick, transparent substance that fills the center of the eye. It is composed mainly of water and comprises about 2/3 of the eye's volume, giving it form and shape. The viscous properties of the vitreous allow the eye to return to its normal shape if compressed. 

The Choroid The choroid contains many blood vessels The choroid is dark in colour as it contains pigment This means that it absorbs light and prevents internal reflection of the light rays