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A - MSRA Ophthalmology [14] > [11] Refractive Errors > Flashcards

[11] Refractive Errors Flashcards

1
Q

What is a refractive error?

A

A problem with focusing light accurately onto the retina due to the shape of the eye

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2
Q

What is ametropia?

A

The global term for any refractive error

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3
Q

What are the different types of refractive errors?

A
  • Myopia
  • Hypermetropia
  • Astigmatism
  • Presbyopia
  • Ansiometropia
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4
Q

What is myopia also known as?

A

Short-sightedness

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5
Q

What is the problem in myopia?

A

Excessive optical power for axial length of eyeball, so focus image in front of retina

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6
Q

What can myopia be classified as?

A
  • Mild
  • Moderate
  • Severe (high-degree)
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7
Q

What is hypermetropia also known as?

A

Far-sightedness

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8
Q

What is the problem in hypermetropia?

A

The eye has insufficient power for it’s refractive length, and therefore light from an object is focused behind the retina, giving rise to a blurred image

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9
Q

What is the problem in astigmatism?

A

Light does not focus evenly on the retina

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10
Q

What is the degree of astigmatism measured in?

A

Cylinders (cyl)

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11
Q

What is presbyopia?

A

Gradual loss of accommodative response

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12
Q

What is the problem in presbyopia?

A

Decline in elasticity of the lens

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13
Q

What is accommodation?

A

The process by which the eye adjusts its’ optical power to maintain a clear image of the object as its distance varies

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14
Q

What are the elements to accommodation?

A
  • Eyes converge
  • Pupil size reduces
  • Lens changes shape and position
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15
Q

What is the timescale for presbyopia?

A

It is a lifelong process that is only clinically significant when reaches certain point

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16
Q

At what point does presbyopia become clinically significant?

A

When patient cannot carry out near-vision tasks such as reading

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17
Q

At what age does presbyopia most commonly occur?

A

After 40 years old

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18
Q

What is anisometropia?

A

When there is unequal refractive errors between both eyes

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19
Q

What level of difference is required to define as anisometropia?

A

Generally 2 diopters

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20
Q

Give an example of when anisometropia is mild with limited consequences

A

Different degrees of myopia in each eye

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21
Q

Give an example of when anisometropia can cause problerms

A

When there are large differences in childhood, especially if one eye is myopic and the other hypermetropic, may be associated with amblyopia

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22
Q

How important are uncorrected refractive errors as a worldwide issue?

A

Accounts for half of avoidance vision impairment globally

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23
Q

What is the purpose of the globe?

A

Receive light from the outside world and transmit it to the brain for processing into a visual image

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24
Q

What are the elements to the function of the globe?

A
  • Image has to be correctly focused onto back of eye

- Information has to be converted to electrochemical signals and transmitted to the brain

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25
Q

What unit is refraction measured in?

A

Dioptres

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26
Q

What does the unit of dioptres describe?

A

The power that a structure has to focus parallel rays of light, i.e. bring them to a point

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27
Q

What does a higher value of dioptres mean?

A

The stronger the focusing ability

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28
Q

Where does focusing happening in the eye?

A
  • Surface of the cornea (80%)

- Surface of lens

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29
Q

Where must the point of focus be in the eye for good vision?

A

The retina

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30
Q

What does the accuracy of refraction depend on?

A
  • Curvature of cornea and lens

- Axial length of the eye (front to back)

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31
Q

What causes the factors affecting the accuracy of refraction to change?

A

The eye growing and ageing

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32
Q

What can myopia arise due to?

A
  • Physiological variation in the length of the eye

- Excessively curved cornea

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33
Q

What does hypermetropia arise due to?

A

Low converging power of the eye lens because of weak action of ciliary muscles, or abnormal shape of the cornea

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34
Q

What does astigmatism arise due to?

A

Variations in the symmetry of the corneal and lens curvature (usually corneal)

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35
Q

How do variations in the symmetry of the cornea/lens curvature cause problems in astigmatism?

A

Light from a point in the visual fields has to focus at a single point on the retina. This is usually achieved by symmetry of the coeval and lens curvatures around their circumference. In astigmatism, variations in the symmetry results in rays failing to focus on a single point

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36
Q

When is anisometropia uncommon?

A

In adulthood

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37
Q

What can cause anisometropia in adulthood?

A

Can occur following trauma and/or refractive/cataract surgery

38
Q

What is the most extreme form of anisometropia?

A

Unilateral aphakia

39
Q

What is unilateral aphakia?

A

When one lens is missing or has been removed

40
Q

What are the risk factors for myopia?

A
  • Family history
  • Prematurity
  • Marfan’s syndrome
  • Stickler’s syndrome
  • Erlers-Danlos syndrome
  • Homocysteinuria
41
Q

Is hypermetropia inherited?

A

Some cases have a family history, but most are sporadic

42
Q

Does astigmatism occur sporadically?

A

Most cases are sporadic, but may be family history or background of certain conditions

43
Q

What conditions might astigmatism occur with?

A
  • Previous eye surgery
  • Previous corneal injury
  • Corneal dystrophies
  • Congenital cataracts
  • Optic nerve hypoplasia
  • Retinitis pigmentosa
  • Albinism
  • Nystagmus
44
Q

How does myopia present?

A

Said to be ‘near-sighted’, whereby distant objects appear to be blurred by close up objects are in focus (unless severe)

45
Q

How does hypermetropia present?

A

Said to be ‘long-sighted’, whereby distant objects are sharply focused but there is difficulty in viewing near objects

46
Q

What might difficulty in viewing near objects give rise to in hypermetropia?

A
  • Eye strain

- Headache

47
Q

What other eye conditions are associated with hypermetropia?

A
  • Corneal dystrophies
  • Congenital cataracts
  • Retinitis pigmentosa
  • Microphthalmia
48
Q

How does astigmatism present?

A

Blurring of vision that is not necessarily associated with obvious far/short-sightedness, although distant viewing is often the more problematic

49
Q

What will the brain try and do in astigmatism?

A

Compensate for the distortion

50
Q

What are the optical symptoms of astigmatism?

A
  • Blurring, distorted, or fuzzy vision
  • Difficulty seeing at night
  • Eyestrain
  • Squinting
  • Eye irritation
  • Headaches
51
Q

What other refraction errors might astigmatism be associated with?

A

Myopia or hypermetropia, and more severe astigmatism may lead to amblyopia

52
Q

What causes of the symptoms of anisometropia?

A

Differing refracting states results in a slight difference in image size. Where the refractive difference is very small, this is not perceived by the patient, but where there is a large difference, the patient experiences symptoms

53
Q

What is the term for when differing refractive states results in a slight difference in image size?

A

Aniseikonia

54
Q

What are the symptoms of anisometropia?

A
  • Diplopia
  • Headaches
  • Photophobia
  • Reading difficulties
  • Nausea
  • Dizziness
  • General fatigue
55
Q

What happens when there is anisometropia in childhood?

A

The brain is more likely to suppress one of the images, so ambylopia develops in the eye in which the image has been suppressed

56
Q

How does presbyopia present?

A
  • Patient finds it difficult to carry out near tasks, and may need brighter lighting conditions for these, or need reading glasses
  • Accommodative lag
  • Tiring with continuous close work
57
Q

What is accommodative lag?

A

Slowed recovery time changing from distance to near tasks, and vice versa

58
Q

What should you assess each eye separately for?

A

Near and distance vision

59
Q

Should patients wear their normal glasses/contact lenses when being assessed for near and distance vision?

A

Yes

60
Q

Why should patients wear their normal glasses/contact lenses when being assessed for near and distance vision?

A

As you are looking for deterioration beyond that already diagnosed/treated

61
Q

What should be done if a patient shows deterioration when testing near and distance vision?

A

Test again using pinhole

62
Q

What does it mean if the patients vision improves when using a pinhole?

A

Uncorrected refractive error may be present

63
Q

How can assessment of refractive errors be done?

A

Via the process of refraction

64
Q

Who performs testing for refractive errors?

A

Optometrist

65
Q

What does the glasses prescription tell you?

A

How strong a lens needs to be to bring the eye back to emmetropia

66
Q

What does a larger prescription mean?

A

A stronger lens is required

67
Q

What format is a glasses prescription?

A

[degree of myopia/hypermetropia]/[degree of astigmatism]x[meridan in which astigmatism lies]

I don’t understand this just rote learn it lol

68
Q

How is myopia managed?

A

A concave (minus) lens is used to correct the problem

69
Q

How is hypermetropia managed?

A

A convex (plus) lens is used to correct the problem

70
Q

How is astigmatism managed?

A

A cylindrical lens is used to ‘neutralise’ the astigmatism

71
Q

What does the axis of the cylinder depend on in astigmatism?

A

The meridian of the asymmetry in the patient’s cornea

72
Q

What is used to correct astigmatism when there is associated myopia or hypermetropia ?

A

A spherocylindrical lens

73
Q

What is the problem with the management of anisometropia?

A

Lens correct is difficult

74
Q

What does lens correction of anisometropia usually involve?

A

Various subtypes of spherical and cylindrical lenses

75
Q

What does the lens used in anisometropia depend on?

A

The type of anisometropia

76
Q

Why is lens correction difficult in anisometropia?

A

The prismatic effects of the lenses typically vary in different positions of gaze, giving rise to further symptoms

77
Q

What are symptoms caused by the lenses in anisometropia collectively known as?

A

Anisophoria, which is lens induced aniseikonic

78
Q

What is the result of symptoms caused by lens correction anisometropia?

A

Many patients tolerate the lenses even less well than the original problem

79
Q

What is often a better solution for the correction if anisometropia?

A

Contact lenses

80
Q

When do patients often managed will with OTC glasses for treatment of presbyopia?

A

If there is no pre-existing eye problem or refractive error

81
Q

What should patients be advised to do when using OTC for presbyopia?

A

Take them off when not carrying out near tasks

82
Q

When will prescription glasses generally be required in presbyopia?

A

If there are pre-existing problems

83
Q

What type of glasses may be used in presbyopia?

A

Bifocal or trifocal

84
Q

Can contact lenses be used in presbyopia?

A

Yes

85
Q

Is surgical correction possible in presbyopia?

A

Yes, but small risk of complications

86
Q

What complications might high-grade myopia be associated with?

A
  • Degenerative fundal changes

- Increased risk of retinal detachment, cataract formation, and glaucoma

87
Q

What complications is persistent hypermetropia associated with?

A

Increased risk of;

  • Glaucoma
  • Squint
  • Amblyopia
88
Q

What are the categories of screening patients for visual impairment?

A
  • Asymptomatic, low-risk patients

- Patients at risk of visual impairment

89
Q

What is considered to be a low risk patient on eye screening?

A

No ocular co-morbidity or family history

90
Q

How often should asymptomatic, low-risk patients have eye screening?

A
  • Every 10 years at 19-40 years old
  • Every 5 years at 41-55 years old
  • Every 3 years at 56-65 years old
  • Every 2 years at >65 years old
91
Q

What patients are considered to be at risk of visual impairment for screening?

A
  • Diabetes
  • Cataracts
  • Macular denigration
  • Glaucoma
  • Significant family history
92
Q

How often should patients at risk of visual impairment have screening?

A
  • Every 3 years at >40 years old
  • Every 2 years >50 years old
  • Every year >60 years old

A - MSRA Ophthalmology [14] (16 decks)

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