Vision 1

Question 1

What is refraction?

Answer 1

Bending of light in order to see an image on the retina

Question 2

When is light bent?

Answer 2

Light bends when it passes from one medium to another

Question 3

Which images need to be bent to be seen on the retina?

Answer 3

When an object is far away the rays will not need to be bent- usually parallel to the image
When an object is up close- then the rays need to be bent more

Question 4

How does refraction occur?

Answer 4

How does it work:
Light bends when it reaches the cornea
Light bends more when it reaches the lens

When an image is closer?
Lens needs to be thicker
This increases the bending power of the lens

Question 5

What property of the cornea allows it to bend light?

Answer 5

Transparency

Question 6

Which is the most powerful bender of light?

Answer 6

The Cornea.

However the lens has the ability to change the power of bending.

Question 7

What is accommodation?

Answer 7

Change in focus on images away or up close by changing how much the image is bent

Question 8

How does accommodation occur?

Answer 8

Lens changes shape and thickens
Pupil constricts
Eyes converge

Question 9

How does the lens change shape and thicken?

Answer 9

• Lens is attached to ciliary body via suspicion ligaments
• Ciliary body contracts= causes lens to become thicker and more spherical
• Thicker lens is more powerful and therefore able to focus better

Question 10

How does the ciliary body contract?

Answer 10

Ciliary muscle contracts 
Causes ciliary body to bulge 
Reduces length of suspension ligaments 
Lens is no longer stretched 
Lens becomes thicker

Question 11

How does the pupil constrict

Answer 11

Contraction of the papillae constrictor

Allows only a few rays of sunshine to pass through

Question 12

How do the eyes converge?

Answer 12

Medial rectus muscle constricts

Question 13

what is a refractive error?

Answer 13

When there is an error with how much we bend the rays

Question 14

What is myopia

Answer 14

Short-sightedness: Close objects are clear, far away objects are hazy

Question 15

what is the cause of myopia?

Answer 15

Due to the eyeball being to long compared to the socket

Rays of light are bent to much compared: they do not reach the retina

Question 16

symptoms of myopia?

Answer 16

• Divergent Squint: particularly in infants and children- eyes do not look straight
• Loss of interest in books/sports- in toddlers/ young children
• Headaches

Question 17

Treatment for myopia

Answer 17

Need to decrease bending power

• Biconcave lens
• Spectacles, contacts
• Laser eye surgery

Question 18

What happens in laser eye surgery

Answer 18

Take away a flap of the Cornea to expose the stroma, Machine can be used to say how much of the stroma needs to be burnt away. Should only be performed on people who struggle a lot with glasses, contacts - machine will not be able to give accurate results on people who have small defects

Question 19

What is hyperopia?

Answer 19

Long-sightedness= can see far away but not up close

Question 20

What is the cause for hyperopia?

Answer 20

Eyeball is too short for the orbit

Image forms behind the retina - it is not bent enough

Question 21

Symptoms of hyperopia?

Answer 21

• Eyestrain after reading/working in young individuals

- Convergent squint in toddlers/children - need to connect straight away in order to prevent damage to eyes

Question 22

Treatment for hyperopia

Answer 22

Biconvex glasses
Contact lenses
Laser eye surgery

Question 23

What is astigamatism?

Answer 23

Images close up and far away both appear hazy

Surface has different curvatures in different meridians

Question 24

Treatment for astigmatism?

Answer 24

Special glasses : cylindrical

- Special contact lenses : Toric

Question 25

What is Presbyopia?

Answer 25

Long-sightedness of the old

As people age, their lens becomes less elastic and mobile as the the rectus muscles of the eye become more strained.

Question 26

How does vision work?

Answer 26

Within the cell membranes of the outer segment of the Rods and cones there are complexes (Rhodopsin) which contain Retinol bound to opsin
Opsin contains vitamin A.
When rods and cones are hit by rays of light, Retinol isomerises (from cis to trans ) and vitamin A is used up:
-Trans-retinol can no longer bind to opsin
-This reaction bleaches the retina and causes a phototransduction cascade of reactions.
-These reactions lead to an action potential being formed and transmitted up the optic nerve.
-The Opsin then needs to be re-formed so another image can be seen.
-This is done using vitamin A.

Question 27

Vitamin A deficiency

Answer 27

-Humans have a 6 month supply of vitamin A In the body
-When they have a diet deficient in vitamin A then they will experience:
Night blindness
Damage to the skin
Ulceration of the cornea
Corneal melting
Silver-like triangles forming in the conjunctiva- Bitot’s spots