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Opthalmology > Vision > Flashcards

Vision Flashcards

1
Q

What is refraction?

A

Light rays bend to form a sharp image on the retina

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2
Q

What is accommodation?

A

The changes occurring in both eyes as it changes focus from a distant object to a close object

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3
Q

When do refractive errors occur?

A

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

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4
Q

When does bending of light occur?

A

When light passes from one optical medium to another

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5
Q

How much of the bending of light depends on what? What is this called?

A

Density of the medium - the refractive medium

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6
Q

Two main benders of the eye

A

Cornea

Lens

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7
Q

What happens when an object comes closer?

A

The eye needs more bending power to focus on an object
The lens becomes thicker and hence more powerful
A clear image is formed on the retina again

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8
Q

What is the most powerful bender of light and its dioptres?

A

Cornea

45D

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9
Q

What bender has the capacity to change its bending power and what is its dioptres?

A

Lens

15D

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10
Q

What distance is considered as infinity and what does this mean for the light rays received in the eye?

A

> 6 metres

Only parallel rays will be received

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11
Q

3 things that happen to make up accommodation

A
  1. lens changes shape (becomes thicker and more spherical)
  2. Pupil constricts
  3. Eyes converge
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12
Q

How does the lens thicken in accommodation?

A

Ciliary body contraction (parasympathetic) causes lens to become thicker and more spherical
When contracts the space in the middle decreases and the suspensory ligaments become lax
When lens isn’t being pulled it flops down and therefore becomes more spherical

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13
Q

How does the pupil constrict in accommodation?

A

The pupil constricts to allow only a few rays (those from the object) to pass through
Pupillary constrictor muscle is the muscles around the border of the pupil which gets parasympathetic innervation

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14
Q

What muscle constricts the pupil?

A

Sphincter pupillae

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15
Q

What muscle causes both eyes to converge and what is this supplied by?

A

Medial rectus muscle

IIIn of both sides

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16
Q

Which of the lateral recti muscles and the medial recti muscles are thicker? Why?

A

Medial recti muscles

Humans spend a lot of time doing ‘close work’

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17
Q

Definition of myopia

A

Short sightedness

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18
Q

Definition of hyperopia

A

Long sightedness

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19
Q

What is astigmatism?

A

Non spherical curvature of cornea (or lens)

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20
Q

Definition of presbyopia

A

Long sightedness of old age

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21
Q

What is the name for perfect vision?

A

Emmetropia

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22
Q

What do you see in myopia?

A

Close objects look clear

Distant objects look hazy

23
Q

Most common cause of myopia

A

Eyeball too long

24
Q

Pathology of myopia

A

When cornea and lens bend ray of light, the image is formed in front of the retina
Therefore bending power of cornea and lens is too much for that eyeball

25
Q

Symptoms of myopia

A 
Headaches
Cant see distant objects
Children 
- lose interest in class
Infants and preverbal children 
- divergent squint 
Toddlers
- loss of interest in people, more interest in books / pictures
26
Q

What type of lenses are used to correct myopia lenses?

A

Biconcave

27
Q

Treatment of myopia

A

Biconcave spectacles
Lenses
Laser eye surgery

28
Q

What is seen when have hyperopia?

A

Close objects look hazy

Distant objects appear clear

29
Q

Cause of hyperopia

A

Eyeball too short

Cornea and lens too flat

30
Q

Pathology of hyperopia

A

Image of the distant object is formed behind the retina
Then accommodative power is used to make the lens thicker which causes the image to form on the retina
When seeing closer objects, he uses more and more power until ultimately all his power is used up

31
Q

Symptoms of hyperopia

A

Symptoms of eyestrain after reading/working

Convergent squint in children/toddlers

32
Q

Treatment of hyperopia

A

Spectacles
Contact lenses
Layer eye surgery
In children/toddlers with divergent squint
- needs immediate correction with glasses to preserve vision in both eyes and prevent a lazy eye

33
Q

What is seen in astigmatism?

A

Close and distant objects appear hazy

34
Q

Pathology of astigmatism

A

Surface has different curvatures in different meridians
Bending of light rays along one axis will never be the same as the other axis
So the image formed is always hazy, whatever the distance of the object

35
Q

Treatment of astigmatism

A

Cylindrical glasses
Laser eye surgery
Toric contact lenses

36
Q

What type of lens is used to treat hyperopia?

A

Biconvex

37
Q

What are cylindrical glasses?

A

Glasses which are only curved in one axis

38
Q

Pathology of presbyopia

A

Lens gets less mobile / elastic with age

So when ciliary muscle contracts, it is not as capable as before to change shape

39
Q

When does presbyopia usually start?

A

5th decade of life

40
Q

Treatment of presbyopia

A

Biconvex “reading glasses”

41
Q

What is visible light?

A

An electromagnetic wave

42
Q

How does photo transduction work?

A

The energy in light waves need to stimulate photoreceptor cells on the retina

43
Q

Definition of phototransduction

A

The conversion of light energy to an electrochemical response by photoreceptors (rods and cones)

44
Q

What do phototransduced rods and cones need to activate?

A

Optic nerve neurones (generate an AP)

45
Q

Each lamellae in rods and cones is made up from what?

A

Cell membrane

46
Q

What is integrated into the cell membrane of lamellae in rods?

A

Visual pigment rhodopsin

47
Q

What is integrated into the cell membrane of lamellae in cones?

A

Opsins S, M and L

48
Q

What happens to visual pigement rhodopsin in rods?

A

Inside the opsin - Vit A compound
This compound absorbs photos to form 11-cis retinal which is quite bendy
It is very sensitive to light - changes chemical form to form an isomer called ALL TRANS RETINAL (same chemical composition but is straight)

49
Q

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

A

Photo transduction cascade

50
Q

What role does vitamin A play in the visual pigment?

A

Visual pigment regeneration

51
Q

What can vit A deficiency result in?

A

Night blindness
Abnormal conjunctiva
Abnormal corneal epithelium

52
Q

Causes of vit A deficiency

A

Malnutrition
Malabsorption syndromes e.g. coeliac
Sprue

53
Q

Presentation of vit A deficiency (in the eyes)

A

Bitot’s spots
Corneal ulceration
Corneal melting - leading to future opacification of the cornea

Opthalmology (8 decks)

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