- It is attached to the skull by three pairs of muscle, which also control its movement.
- It is made up of three main layers;sclerotic layer, choroid and the light sensitive retina.
Sclerotic layer
- Outermost white part situated at the sides and back of the eye.
- It is made up of collagen fibres.
- It protects the eye and gives its shape.
Cornea
- This is the transparent front part of the sclera that allows light to pass through.
- It is curved, bulging at the front. It thus reflects light rays hence helps to focus light rays onto the retina.
Choroid
- The second or middle layer.
- It has many blood vessels that supply nutrients to the eye and remove metabolic wastes from the eye.
- It has dark pigments to absorb stray light and prevent its reflection inside the eye.
Ciliary body
- Is glandular and secretes aqueous humour.
- It has blood vessels for supplying of nutrients excretion and gaseous exchange.
- It has ciliary muscles - which contract and relax to change the shape of lens during accommodation.
Suspensory ligaments
- Are inelastic and attach the lens onto the ciliary body holding it in position.
Lens
- Biconvex in shape - to refract light.
- Crystalline and transparent to allow light to pass through and focus it on to the retina.
Aqueous humour
- Found between lens and the cornea.
- Transparent to allow light to pass through it.
- It is watery thus helping in focusing.
- Helps maintain shape of eye ball.
- To convey nutrients and oxygen to cornea, and remove waste products.
Iris
- The coloured part of the eye has an opening - the pupil at the centre.
- Iris has circular and radial muscles which controls size of the pupil, hence the amount of light entering the eye through the pupil.
Vitreous humour
- It is a fluid.
- Found between lens and retina.
- Is viscous and gives eye the shape.
- It is transparent and refracts light.
Retina
- Retina contains light sensitive cells and is situated at the back of the eye.
- There are two types of light sensitive cells in the retina:
- Rods - are sensitive to low-intensity light and detect black and white. Nocturnal mammals have more rods.
- Cones - are sensitive to high intensity of light;
- Diurnal mammals have more cones.
Fovea centralis
- Fovea centralis (yellow spot) is the most sensitive part of the retina.
- Consists mainly of cones for accurate vision (visual acuity).
Optic nerve
- Optic nerve, has neurons for transmission of impulse to the brain for interpretation.
Blind spot
- Blind spot is located at the point where the optic nerve leaves the eye on its way to the brain.
- It is not sensitive to light it has no rods or cones.
Eye lid
- Eye lid is a loose skin that covers the eye. It closes by reflex action.
- Protects it from mechanical damage and from too much light.
Eyelashes
-Prevent dust and other particles from entering eye.
Conjuctiva
- It is transparent and thin and allows light to pass through.
- It is a tough layer that is continuous with the epithelium of the eye lids.
- It protects the cornea.