The Human Eye

Question 1

Name the layers found in The Eye

Answer 1

Sclerotic coat (sclera) - outermost layer
Choroid - middle layer
Retina - innermost layer

Question 2

What are the functions of the tear gland?

Answer 2

It secretes tears to

• wash away dust particles
• moisten the cornea for the absorption of dissolved oxygen
• lubricates the conjunctiva to reduce friction when the eyelids move

Question 3

What is the pupil and its function?

Answer 3

The pupil is a hole in the centre of the iris that allows the entry of light entering The Eye, its size is controlled by muscles in the iris

Question 4

What is the cornea and its function?

Answer 4

A dome shaped transparent layer that refracts light rays into The Eye

Question 5

What is the function of the eyelid?

Answer 5

To protect the cornea from mechanical damage; squinting also prevents excessive entry of light which may damage the retina
Blinking spreads tears over the eyes so that dust can be wiped off

Question 6

What is the function of the eyelash?

Answer 6

To shield The Eye from dust particles

Question 7

What is the iris and its function?

Answer 7

A circular sheet of two sets of involuntary and antagonistic muscles ; circular and radial
Contains a pigment which gives The Eye its colour

Question 8

What is the conjunctiva and its function?

Answer 8

Thin mucus membrane covering the sclera

Secretes mucus to keep the front of the eyeball moist

Question 9

What is the sclerotic coat and its functions?

Answer 9

Tough white outer covering of the eyeball that is continuous with the cornea
Eye muscles are attached to this layer, facilitating the movement of the eyeball
Protects the eyeball from mechanical damage

Question 10

What is the choroid and its function?

Answer 10

Black pigmented middle layer of the eyeball
Prevents the internal reflection of light
Contains blood vessels which transports oxygen and nutrients to the eyeball and removes metabolic waste products

Question 11

What is the retina and its function?

Answer 11

The innermost layer of The Eye wall containing light-sensitive cells known as photoreceptors - consists of rods and cones which have different functions
Connected to nerve fibres from the optic nerve

Question 12

What is the function of photoreceptors in the retina?

Answer 12

Converts light waves into nerve impulses which relays information to the brain

Question 13

What are the functions of cones in the retina?

Answer 13

There are 3 different types of cones which contains either red blue and green pigment that each absorbs light of different wavelengths work together to enable one to see a variety of colours in bright light

Question 14

What are the functions of rods?

Answer 14

Stimulated by very dim light, enables one to see in dim light but only in black or white
Contains a pigment called visual purple which becomes bleached in bright light preventing nerve impulses from being transmitted to the brain

Question 15

What is the fovea and its function?

Answer 15

A small yellow depression where images are focused ,
Contains only cones
Enables a person to have detailed colour vision in bright light
Vision is sharpest here

Question 16

What is the blind spot and its function?

Answer 16

Region where the optic nerve leaves The Eye

Does not contain photoreceptors and thus is not sensitive to light

Question 17

Function of the optic nerve?

Answer 17

Transmits nerve impulses to the brain when the photoreceptors are stimulated

Question 18

What are the lens and its function?

Answer 18

Transparent circular biconvex structure

Shape or thickness can be changed in order to refract light onto the retina

Question 19

What is the ciliary body and its function?

Answer 19

contains ciliary muscles which control the curvature and thickness of the lens

Question 20

What are Suspensory ligaments ?

Answer 20

Ligaments that attaches the edge of the lens to the ciliary body

Question 21

What is the aqueous chamber and its function?

Answer 21

Space between the lens and the cornea

Is filled with aqueous humour

Question 22

What is aqueous humour and its function?

Answer 22

A transparent watery fluid that
Keeps the front of the eyeball firm and
Refracts light onto the pupil

Question 23

What is the vitreous chamber?

Answer 23

The space behind the lens

Contains vitreous humour

Question 24

What is the vitreous humour and its function?

Answer 24

A transparent jelly-like substance that

Keeps the eyeball firm and refracts light onto the retina

Question 25

What is pupil reflex and its function?

Answer 25

A reflex response to changes in light intensity; protects The Eye from excessive light exposure , which could damage the retina

Question 26

Pathway of pupil reflex?

Answer 26

Stimulus (change in light intensity) -> receptor ( retina ) -> sensory neurone in the optic nerve -> brain -> motor neurone -> effector (iris muscles)

Question 27

What is the pathway for the formation of an upright image at the brain?

Answer 27

The inverted image is formed on the retina
Light sensitive cells (rods and cones) are stimulated
Nerve impulses generated are transmitted through the optic nerve
Nerve impulses reach the optic centre of the brain
Te brain interprets the information and forms an upright image

Question 28

What happens when one tries to focus on a nearby object?

Answer 28

The light rays from a near object are divergent. A greater angle of refraction is needed to bring them into focus on the retina.
The ciliary muscles contract, relaxing their pull on Suspensory ligaments. The Suspensory ligaments slacken , relaxing their pull on the lens.
The lens become thicker and more convex, decreasing the focal length
Light rays are sharply focused on the retina , stimulating the photoreceptors
Nerve impulses generated are transmitted to the brain via the optic nerve
The brain interprets the impulses and the person sees the near object

Question 29

What happens when one tries to focus on a far object?

Answer 29

Light rays from a distant object are almost parallel, thus a smaller angle of refraction is needed to bring them into focus. The ciliary muscles relax, pulling on Suspensory ligaments
The Suspensory ligaments becomes taut, pulling on the edge of the lens
Causing it to become thinner and less convex, increasing the focal length
Light rays are sharply focused on the retina
Nerve impulses generated are transmitted to the brain via the optic nerve
The brain interprets the impulses and the person sees the far object