STRUCTURE AND FUNCTION OF THE EYE

All human and most animals have 2 eyes embedded in a socket called orbits. The eye is attached by muscle fibre and can easily rotate in it orbit. It helps an animal to see and locate object. The human eye resemble the camera in three ways.

• They are both convex lens
• Eye lise the retina as scree while the camera use film as screen
• Iris to control light while diaphgram to control light

The eye can be see to consist of three main layers;

1. The sclera(the white part of the eye) it is the outermost layer of the eye. It is a tough protective layer around the eye ball consisting of inelastic fibre. It support and maintain the shape of the eye ball.
2. The choroid:  this is the tissues that line the inside of the sclera. It is a pigment layer( contain black pigment) the cell and it black pigment prevent internal reflection of light by absorbing the light rays
3. Retina : this is the layer of cell sensitive to light. This layer has two types of light sensitive cells know as the rod and cones only the cones are sensitive to colour light. While the rod are sensitive to white and black light mammal with cones in their retina are able to distinguish between colour.
4. Cornea: it is transparent frot part of the eye. It help to refract light ray as it enter into 13 eye
5. The conjunctiva: it is a thin transparent membrane. It covers and protect the expose part of the eye and lines the inner surface the eye leds
6. Aqeous humour: it is a watery fluid similar to blood plasma to maintain the shape of the front part of the eye. It also carries nutrient such as glucose, protein to the cornea and lens
7. Virtrous humour: it is a transparent jelly lid material which maintain the shape of the eye
8. Iris : this is the round colour part of the eye. It regulates the amount of light that reaches the retina by controlling the size of the pupil
1. Lens: it is soft and transparent dish held in place suspensory ligament. It function in focusing images to the retina
10. Conjunctiva: it is a transparent membrane it covers and protect the exposed part of the eye and lines the inner surface of the eyelids

HOW THE EYE IS PROTECTED

1. The skull have two deep cavity called orbit that enclose and protect all but the front part of the eye
2. A tip layer of fat is deposited around the eye ball which hushions it against shock
3. A transparent skin called the conjunctiva covers the exposed surface of the eye. The blink reflex protect the eyes by involuntary losure of the eye kies
4. The lushes forms a net infront of the eye which traps layers of air born particles

FUNCTIONS OF THE EYES

The eyes have 2 main functions

• Accommodation
• Image formation

1. Accomodation:  accommodation refers to the ability of the eyes to focus on both far and near by objects. This function of the eye is greatly control by the iris. Which determinate the amount of light that enter the pupils. The iris is made up of radial and ciliary muscles.

When the eye is leaking at distance object

• The circular ciliary muscle relax
• The radial ciliary muscle contract
• The suspensory ligament are pulled tied
• The lens becames thinner and less convex
• The refractive power of the lens is reduce
• Parallel light rays from the distance object are focus on the forvea

When the eye is looking at a near by object

• The cicular ciliary muscle contract
• The radial ciliary muscle relax
• The suspensory ligament slackens or weakens
• The lens became thicker and less convex
• The refractive power of the lens increase
• Diverging rays from the near by object are brought to focus on the forvea

2. Image formation:

How the eye function in image formation

• Light rays from an external object entering the eye pass through the conjuction, the curve surface of the cornea, the aqeous humour, the virteous humour and the less to the retina
• The light rays are refracted as they passs through the various region of the eye and are finally brought to a focus on the forvea of the retina
• The cornea carries out the greatest of amount of reflection or bending of the light rays
• The lens help in accurately focusing light ray from both distance and near object an the forvea
• The light falling on the retina stimulate the light, sensitive cells impulses are send through the optic nerve to the visual centre of the fore brain
• The brain enterprete the impulses and an upright impression of the nature, size, colour and distance of the object from the eye is perceived

DEFECTS OF THE EYE

ADJUSTMENT MADE BY THE EYE IN DIM LIGHT AND BRIGHT LIGHT

• The retina has light sensitive cells (rods and cones) rods are sensitive to dim light or low light and cones are sensitive to bright light or high light intensity
• Cones are concentrated in a spot called the forvea, to form the most sensitive part of the retina
• Optic nerves transmits nerve impulses to the brain.