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MBChB - Y2 - Systems - Nervous System > Vision 1 > Flashcards

Vision 1 Flashcards

1
Q

What is meant by accomodation?

A

How much we bend light rays

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2
Q

When is an object considered to have parallel rays of light?

A

Anything beyond 6 metres

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3
Q

What is meant by refraction?

A

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

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4
Q

What are the transparent parts of th eye?

A

Cornea, lens, aqueous humour and vitreous humour

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5
Q

What is the power of the cornea and the lens?

A

Cornea - 45 D

Lens - 15 D

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6
Q

What three things comprise accomodation?

A

Lens shape - becomes thicker and more spherical

Pupil constricts

Eyes converge

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7
Q

What is responsible for the lens becoming thicker?

A

Ciliary muscle contracts making the ciliary body bulge. Ciliary body contraction is under parasympathetic control.

The lens is normally under stretch

Ciliaris muscle is under control by the third cranial nerve

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8
Q

Which muscle is repsonsible for the constriction of the pupil when looking close up at an object? What is the innervation

A

Constrictor pupillae

It is the concentric muscle around the border of the pupil. Gets parasympathetic innervation from cranial nerve 3

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9
Q

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

A

Because humans spend a lot of time doing close work and it is our medial retus muscles that are responsible for convergeance

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10
Q

What is the definition of the following?

  • Myopia
  • Hyperopia
  • Astigmatism
  • Presbyopia
  • Emmetropia
A
  1. Myopia – short-sightedness
  2. Hyperopia – long-sightedness
  3. Astigmatism – non-spherical curvature of cornea (or lens)
  4. Presbyopia – long-sightedness of old age
  5. Emmetropia - perfect vision
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11
Q

What is the cause of myopia?

A

Most common cause is that the eyeball is too long

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12
Q

What are symptoms of myopia?

A

Headaches

‘Can’t see blackboard/distant objects’

Infants and preverbal children have a divergent squint

Toddlers have a loss of interest in sports and people - more intersted in books and pictures

Child loses interest in class

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13
Q

What is the treatment for short sightedness?

A

Spectacles

Contact lenses

Laser eye surgery

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14
Q

What is the cause of hyperopia?

A

Eyeball is too short or cornea and lens is too flat

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15
Q

Where is the image formed in hyperopia?

A

Image is formed behind the retina

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16
Q

Why can’t people who are long sighted see objects close up?

A

They are aalready suing a large portion of their accomodative power at a relatively long distance

Their accomodative power eventually expires at a longer distance than normal

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17
Q

What are symptoms of long sightedness?

A

Eyestrain after reading/working on the computer in a young individual.

If a toddler has a convergent squint, it needs immediate correction with glasses/lenses to preserve vision in both eyes and prevent a lazy eye

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18
Q

What type of lenses are indicated for people with long sight?

A

Biconvex

19
Q

What is an astigmatism?

A

Surface of the eye has different curvatures in different meridians - bending of light rays on one axis will never be the same as that of the other axis

20
Q

What type of lens is needed for an astigmatism?

A

Cylindrical glasses - which are curved only on one axis

21
Q

What is treatment besides glasses for an astigmatism?

A

Laser eye surgery

Toric lenses

22
Q

What is presbyopia, and why does it occur?

A

Longsightedness of old age

Happens as a result of the lens becoming less mobile and elastic, when the ciliary muscle contracts it is less able to change its shape

23
Q

When does presbyopia occur?

A

5th Decade of life

24
Q

What is corection of presbyopia?

A

Using boconvex reading glasses

25
Q

What do the following columns indicate?

A

RE - means right eye

LE - left eye

BC - Base curve - the curve of your contact lens, measured in millimetres

DIA - diameter, so refers to the size of the lens

SPH - the lens power you need to achieve emmetropia

26
Q

What is meant by phototransduction?

A

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

27
Q

Where does phototransduction occur in the rods and cones?

A

The outer segments of the rods and cones (effectively their dendrites)

28
Q

What is the structure of the rods and cones?

A

Inner segment contains organelles

Outer segment contains stacks of disks / lamellae which have photoreceptors

29
Q

What is the visual pigment embedded in the cell membrane of the lamellae of rods?

A

Rhodopsin

30
Q

What is the visual pigment embedded in the cell membrane of the lamellae of cones?

A

Cone opsins S,M and L

These molecules differ in their spectral sensitivity

Cones and rods respond to different wavelengths of light

31
Q

Define chomophore

A

An atom or group whose presence is responsible for the colour of a compound.

32
Q

What are the two main compnents of rhodopsin?

A

Opsin and 11-cis retinal

33
Q

What happens when light falls on 11-cis retinal?

A

It isomerises to all-trans retinal

34
Q

What happens to rhodopsin after the formation of all-trans retinal?

A

All- trans retinal cannot fit into the opsin. So rhodopsin splits. This results in BLEACHING of the visual purple chromophore nesting in the opsin. This molecule formed from dietary Vitamin-A.

35
Q

What role does vitamin A play in the visual pigment?

A

Visual pigment regeneration

36
Q

When the photoreceptor cells are at rest (in the dark), what state are they in?

A

Depolarized state - by open sodium and calcium channels

37
Q

What is vitamin A used to form?

A

11 cis Rol from all trans retinol (all trans retinal) which is used to regenerate 11 cis retinal

38
Q

How does phototransduction stimulate the retinal cell?

A

Rhodopsin is activated

Results in a sodium channel closing

Hyperpolarization of photoreceptor cell

This is transmitted by a flux of calcium ions to the synapse with bipolar cell

39
Q

Which are more numerous rods or cones?

A

Rods

40
Q

What is the effect of vitamin A deficiency?

A

Night blindness

Vitamin A is essential for a healthy epithelium, so conjunctivae and corneal epithelium are abnormal

41
Q

When does vitamin A deficiency occur?

A

Conditions such as malnutrition

Malabsorption syndromes such as coeliac disease and sprue

42
Q

What is often the first indication of vitamin A deficiency?

A

Bitot’s spots - present in conjunctivae

Corneal ulceration

Corneal melting which leads to future opacification of the cornea

43
Q
A

MBChB - Y2 - Systems - Nervous System (48 decks)

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