The Eye

Question 1

where is the eye located

Answer 1

bony sockets of the skull called orbits, and have muscles attached to move them

Question 2

orbit

Answer 2

protects the back of each eye from damage

Question 3

eyelids and eyelashes

Answer 3

protect the front from foreign particles by blinking, involuntary action

Question 4

tears

Answer 4

produced by tear glands above each eye,

keep the eyes moist, wash away foreign particles and contain an enzyme (LYSOZYME) that destroys micro-organisms, prevnting infections

Question 5

conjunctiva

Answer 5

thin, transparent
layer continuous with the lining
of the eyelids. Protects the cornea

conjunctivitis- inflammation and irritation of the conjunctiva causing the eye to appear reddish or pink, virus, illness, fungi, air pollution

Question 6

cornea

Answer 6

transparent front
part of the sclera. Refracts
(bends) light rays onto the retina

Question 7

aqueous humour

Answer 7

Colourless fluid. Maintains the shape of the cornea

Question 8

lens

Answer 8

– transparent, elastic, biconvex structure. Makes fine adjustments
to focus light rays on the retina

Question 9

pupil

Answer 9

hole in the centre of the
iris. Allows light to enter the eyeball

Question 10

iris

Answer 10

coloured disc composed of
muscle. Controls the amount of
light entering the eye

Question 11

suspensory ligament

Answer 11

attaches
the lens to the ciliary body

Question 12

ciliary muscle

Answer 12

– circular ring of muscle
running through the ciliary body. Alters the shape of the lens during
accommodation

Question 13

vitreous humour

Answer 13

jelly-like fluid.Maintains the shape of the eyeball

Question 14

sclera

Answer 14

– tough,white,fibrous coat.Protects the eyeball

Question 15

choroid

Answer 15

contains blood vessels which supply the retina with food and oxygen, and melanin to prevent reflection of light inside the eye

Question 16

fovea

Answer 16

contains cones only.The most sensitive part of the retina, most light rays are focused here

Question 17

retina

Answer 17

contains light-sensitive cells called rods and cones.Where the image forms

Question 18

optic nerve

Answer 18

carries impulses from the retina to the brain

Question 19

blind spot

Answer 19

point where theoptic nerve leaves the eye. No light-sensitive cells are present

Question 20

Image formation

Answer 20

In order to see, light rays from an object must berefracted (bent) as they enter the eye so that they form a clear image of the object on the receptor cells of the retina. Being convex in shape, both the cornea and the lens refract the light rays.

Question 21

Detection of light intensity and colour by the eye

Answer 21

The retina is composed of two types of specialised light-sensitive cells or photoreceptors:

Question 22

Rods role in image formation

Answer 22

Rods function in low light intensities. They are responsible for detecting thebrightness of light andare located around the sides of the retina. Images falling on the rods are seen in shades of blackand white only.

Question 23

Cones role in image formation

Answer 23

Cones function in high light intensities. They are responsible for detecting colour and fine detail, and are mainly located around the back of the retina. The fovea is composed entirely of cones which are packed closely together. There are three types that detect either the red, green or bluewavelengths of light.

Question 24

Short sight, myopia

Answer 24

OPEN V-SHAPED

LENS ARE DIVERGING, CONCAVE CAVE IN

A person with short sight can see near objects, but distant objects are out of focus. Light rays from near objects focus on the retina; light rays from distant objects focus in front of the retina. Short sight occurs if the eyeball is too long
from front to back or if the lens is too curved (thick). It is corrected by wearing diverging (concave) lenses as spectacles or contact lenses.

Question 25

Long sight (hypermetropia)

Answer 25

A person with long sight can see distant objects, but near objects are out of focus. Light rays from distant objects focus on the retina; light rays from near objects focus behind the retina. Long sight occurs if the eyeball is too short from front to back or if the lens is too flat(thin). It is corrected by wearing converging (convex) lenses as spectacles or contact lenses. CONVERGING CONVEX POUTS OUT DIAGRAM HAS LIGHT RAYS THAT ARE QUADILATERAL

Question 26

Old sight (presbyopia)

Answer 26

As a person ages, the lens loses its elasticity and the ciliary muscles weaken. The lens is less able to curve and the person finds it increasingly difficult to see near objects. It is corrected by wearing converging lenses for looking at near objects.

Question 27

Glaucoma

Answer 27

Glaucoma is a condition in which the pressure of the fluid within the eye increases due to the flow of aqueous humour from the eye being blocked. If left untreated, the optic nerve becomes damaged and it can lead to blindness. The most common type develops slowly and causes a gradual loss of peripheral (side) vision. Glaucoma is treated with: eye drops to reduce fluid production or improve the flow of fluid from the eye, or by laser treatment or an operation to open the drainage channels