Vision 1

Question 1

Refraction in the eye

Answer 1

Light rays bend to form a sharp image on the retina

Question 2

Accommodation

Answer 2

We can focus on far off or near objects by changing how much we bend the light rays

Question 3

Refractive errors

Answer 3

Sometimes there is a mismatch between how much we bend light rays

Question 4

Refraction

Answer 4

Bending of light when it passes from one optical medium to another

Question 5

What is transparent to allow light to fall on the retina?

Answer 5

• Cornea
• Aqueous humor
• Lens
• Vitreous humor

Question 6

What are the 2 main areas of bending of light?

Answer 6

The cornea is the most powerful bender of light (45D) but the lens (15D) has the capacity to change its bending power

Question 7

What happens to the lens as an object comes closer?

Answer 7

The eye needs more bending power to focus on the object, therefore the lens becomes thicker and hence more powerful.

Question 8

What accommodative power does our eyes have?

Answer 8

To change focus from distant objects (infinity) to close objects (20cm)

Question 9

What are the 3 components of accommodation?

Answer 9

• Lens changes shape
• Pupil constricts
• Eyes converge

Question 10

What shape change does the lens undergo during accommodation?

Answer 10

Becomes thicker and more spherical

Question 11

Why does ciliary body contraction result in the ability to focus on close objects?

Answer 11

• Ciliary body contraction (parasympathetic) causes lens to become thicker and more spherical
• A thicker lens is more powerful: can focus close objects

Question 12

How does the lens become thicker?

Answer 12

• Ciliary muscle contracts making the ciliary body bulge
• Space in the middle decreases
• Suspensory ligaments become lax
• Lens is no longer under stretch
• Lens becomes thicker

Question 13

Why does the pupil constrict when focussing on a close object?

Answer 13

We require a sharp focus

Question 14

How is a sharp focus created?

Answer 14

Pupillary constriction to allow only a few rays (those from the object) to pass through

Question 15

What muscle is responsible for constriction of the pupil?

Answer 15

Pupillary constrictor (sphincter pupillae) is a concentric muscle around the border of the pupil which gets parasympathetic innervation

Question 16

What muscles are responsible for convergence of our eyes?

Answer 16

We use our medial rectus of both eyes to converge

Question 17

Why are our medial recti thicker than our lateral recti muscles?

Answer 17

Humans spend a lot of time doing close work

Question 18

Convergence

Answer 18

Turning inwards of our eye to focus on a close up object

Question 19

Myopia

Answer 19

Short sightedness

Question 20

Hyperopia

Answer 20

Long sightedness

Question 21

Astigmatism

Answer 21

Non-spherical curvature of cornea(or lens)

Question 22

Presbyopia

Answer 22

Long sightedness of old age

Question 23

Give 4 examples of refractive errors.

Answer 23

• Myopia
• Hyperopia
• Astigmatism
• Presbyopia

Question 24

Emmetropia

Answer 24

Perfect vision

Question 25

Describe myopic vision.

Answer 25

- Close objects look clear - Distant objects appear hazy - Image formed short of the retina

Question 26

What is the most common cause of myopia?

Answer 26

Eyeball is too long

Question 27

Why can people with myopia see close up objects clearly?

Answer 27

- The bending power of the cornea and lens is too much - Therefore, when an object is brought closer the rays coming from it are divergent and then this bending power comes to use

Question 28

What are the symptoms of myopia?

Answer 28

- Headaches - Complain of not being able to see the board at school - Divergent squint in infants and preverbal children - Loss of interes in sports/ people with greater interest in books and pictures in toddlers - Teachers may notice child losing interest in class

Question 29

What is the treatment for myopia?

Answer 29

The bending power needs to be decreased by biconcave lenses - Spectacles - Contact lenses - Laser eye surgery

Question 30

Describe hyperopic vision.

Answer 30

- Close objects look hazy - Distant objects appear clear - Image formed behind retina

Question 31

What are the main causes of hyperopia?

Answer 31

- Eyeball too short | - Lens too flat

Question 32

Why are longsighted people unable to see close up objects?

Answer 32

- They automatically start to use up their accommodative power to see far away things. - They use more and more of this power up as the object moves closer until there is no more accommodative power - Therefore the find it difficult to see clos up objects

Question 33

What are the symptoms of hyperopia?

Answer 33

- Symptoms of eyestrain after reading/working on computer in the young - Convergent squint in children/toddlers

Question 34

If a child has a convergent squint what must be done?

Answer 34

Immediate correction to preserve vision in both eyes and prevent a lazy eye

Question 35

What is the treatment for hyperopia?

Answer 35

Biconvex glasses alleviates use of glasses for focussing distant objects and rests the power for accommodative power - Contact lenses - Laser eye surgery

Question 36

Describe astigmatic vision.

Answer 36

Close and distant objects appear hazy

Question 37

Why is the image formed always hazy in astigmatism?

Answer 37

- Surface has different curvatures in different medians - So the bending of light rays along one axis will never be the same as that of the other axis - Therefore image is always hazy

Question 38

What is the treatment for astigmatism?

Answer 38

Cylindrical glasses - Laser eye surgery - Toric contact lenses

Question 39

What causes presbyopia?

Answer 39

- With age the lens gets less mobile/elastic - So when the ciliary muscle contracts it is not as capable as before to change shape - Therefore it becomes difficult to see near objects

Question 40

When does presbyopia usually occur?

Answer 40

Around about the 5th decade

Question 41

How is presbyopia treated?

Answer 41

Biconvex glasses

Question 42

What kind of wave is visible light?

Answer 42

Electromagnetic

Question 43

What does the energy in light waves need to stinumlate?

Answer 43

Photoreceptor cells on the retina

Question 44

Phototransduction

Answer 44

The conversion of light energy to an electrochemical response by the photoreceptors

Question 45

What cells in the human eye are the photoreceptors

Answer 45

Rods and cones

Question 46

What do the phototransduced rods and cones need to activate?

Answer 46

Optic nerve neurons to generate an action potential

Question 47

Describe the structure of rod and cone cells.

Answer 47

- Synaptic terminal - Axon - Nucleus forming (outer nuclear layer of retina) - Inner segment containing cell organelles - Outer segement containg discs/ lamellae

Question 48

What is each lamellae made up of?

Answer 48

Cell membrane

Question 49

What is integrated into the cell membrane of the lamellae?

Answer 49

The visual pigment rhodopsin in rods and opsins S,M and L in cones

Question 50

How do opsins and rhodopsins differ?

Answer 50

In their spectral sensitivity

Question 51

What happens to 11-cis retinal when light falls on it?

Answer 51

Isomerises to all-trans retinal

Question 52

The chromophore nesting in the posit is formed from what?

Answer 52

Dietary vitamin A

Question 53

What is rhodopsin formed from?

Answer 53

- Opsin | - 11-cis retinal

Question 54

How does bleaching of the visual purple occur?

Answer 54

-All trans retinal cannot fit into the opsin so rhodopsin splits resulting in bleaching

Question 55

How does bleaching of the visual pigment result in photo transduction?

Answer 55

Phototransduction cascade

Question 56

What role does vitamin A play in the visual pigment?

Answer 56

Visual pigment regeneration

Question 57

How do the photoreceptors differ form other cells in the body?

Answer 57

When at rest (in the dark) they are kept in a depolarised state by open Na/Ca channels

Question 58

If there is not a constant supply of vitamin A what will be former?

Answer 58

Retinyl esters

Question 59

What will any condition affecting vitamin A absorption result in?

Answer 59

- Affect vision: night blindness | - Essential for healthy epithelium so can cause abnormalities in conjunctiva and corneal epithelium

Question 60

What conditions can vitamin A deficiency occur in?

Answer 60

- Malnutrition | - Malabsorption syndromes such as coeliac disease, sprue

Question 61

What is sometimes the first indication of vitamin A deficiency?

Answer 61

Bitot's spots in the conjunctiva