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Neuro AM > Refraction and accommodation > Flashcards

Refraction and accommodation Flashcards

1
Q

What is refraction?

A

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

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2
Q

What does how much light bends depend on?

A

Refractive index- density

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3
Q

At what points in the eye does light bend?

A

Cornea and lens

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4
Q

How does a clear image form on the retina?

A

Light waves from an object bend at the cornea and lens to form a clear image on the retina

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5
Q

What happens when an object comes closer?

A

The eye needs more “bending power” to focus on an object

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6
Q

What are the refractory media?

A

Cornea and lens

Aqueous and vitreous humour

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7
Q

What are the characteristics of the cornea and lens?

A 
Cornea= most powerful
Lens= can alter its "bending power"
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8
Q

What is accommodation?

A

Capacity of our eyes to change focus from distant to close objects

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9
Q

What rays do we see of distant and close objects?

A 
Distant= parallel rays
CLose= divergent rays
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10
Q

What must happen for close objects to be seen clearly?

A

Have to be refracted more due to the divergent rays

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11
Q

What 3 things comprise accommodation?

A

Lens changes shape
Pupil constricts
Eyes converge

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12
Q

What happens to the lens if an object comes closer?

A

Becomes thicker and more spherical in order to increase its refractive index

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13
Q

How does the lens becomes thicker and more spherical?

A

Ciliary body contraction causes ciliary body to bulge
Space in the middle decreases
Suspensory ligaments become lax, and the lens is no longer under stretch and so becomes thicker

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14
Q

What happens to the pupil if an object comes closer?

A

Constricts to only allow a few light rays through

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15
Q

How does the pupil constrict?

A

Sphincter pupillae contracts with parasympathetic innervation

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16
Q

What happens to the position of the eyes when an object comes closer?

A

Converge in order to see the object better

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17
Q

How do the eyes converge?

A

Medial rectus of both eyes contracts

18
Q

What is myopia?

A

Short sightedness

19
Q

What causes myopia?

A

Bending power of the eyes is too high and the image converges before the retina

20
Q

Why can bpeople with myopia see things close up?

A

he high bending power is put to use and close objects are clear

21
Q

How is myopia corrected?

A

Bi concave lenses

22
Q

What are the symptoms of myopia?

A

Headaches

Complain of not being able to see the board at school

23
Q

What are the symptoms of myopia in infants and preverbal children?

A

Divergent squint

24
Q

What are the symptoms of myopia in toddlers?

A

Loss of interest in sports and people

More interest in books and pictures

25
Q

What is hyperopia?

A

Long sightedness

26
Q

What causes hyperopia?

A

Bending power not high enough and image focuses behind retina
The person then automaticity has to use accommodative power and make lens thicker to see objects far away, and has no more accommodative power when objects come closer

27
Q

How is hyperopia corrected?

A

Biconvex lenses

28
Q

What are the symptoms of hyperopia?

A

Eyestrain and headaches

Convergent squint in children

29
Q

Why does hyperopia need immediate corrected in children?

A

Convergent squint can cause lazy eye

30
Q

What is astigmatism?

A

Non spherical curvature of cornea or lens- rugby ball rather than football shape

31
Q

What does astigmatism cause?

A

Bending of light rays on the 2 axes will never be the same and so the image on the retina will always be blurry

32
Q

Hw is astigmatism corrected?

A

Cylindrical glasses- only curved in one axis

Toric contact lenses

33
Q

What is presbyopia?

A

Longsightedness of old age

34
Q

What causes presbyopia?

A

With age, the lens gets less mobile and elastic, so is less capable of becoming more spherical to see close objects

35
Q

How is presbyopia treated?

A

Biconvex reading glasses

36
Q

What is transduction?

A

Process by which light is converted to electrical signals in the rod cells, cone cells and photosensitive ganglion cells in the retina

37
Q

What carries signals to the optic nerve?

A

Hyperpolarisation through the cells

38
Q

What happens in the optic nerve re transduction?

A

Action potential produced

39
Q

What is the phototransduction cascade?

A

Bleaching of the visual pigment

40
Q

How do the rods and cones bleach?

A

Contain opsin nd rhodopsin which bleach

41
Q

What is visual pigment regeneration?

A

Process by which cells “unbleached”, involving vitamin A

Neuro AM (38 decks)

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