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Duke Elder > Lens, cataracts and optics > Flashcards

Lens, cataracts and optics Flashcards

1
Q

What is the refractive power of the lens?

A

20D

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2
Q

What is the refractive power of the lens?

A

20D

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3
Q

Axial length of the eye in:

a) newborn
b) child
c) adult

A

a) 16mm
b) 22.5mm
c) 24mm

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4
Q

What is the length from the lens to the retina in adults?

A

17mm

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5
Q

What is the most common cause of myopia?

A

axial length >24mm

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6
Q

What conditions increase the power of the eye?

A

keratoconus

nuclear sclerotic cataract

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7
Q

What is high myopia?

A

> -6

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8
Q

Management of myopia

A 
spherical concave lenses to diverge light (minus spheres)
keratorefractive surgery (ablation of central corneal curvature)
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9
Q

Management of myopia

A 
spherical concave lenses to diverge light
keratorefractive surgery (ablation of central corneal curvature)
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10
Q

What factors can cause hypermetropia?

A

axial length <24mm

refractive power too week e.g. aphakik patients

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11
Q

Axial length of the eye in:

a) newborn
b) child
c) adult

A

a) 16mm
b) 22.5mm
c) 24mm

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12
Q

What is the length from the lens to the retina in adults?

A

17mm

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13
Q

What is the most common cause of myopia?

A

axial length >24mm

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14
Q

What conditions increase the power of the eye?

A

keratoconus

nuclear sclerotic cataract

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15
Q

What is high myopia?

A
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16
Q

What can be done to prevent myopia?

A

atropine and pirenzipine drops
outdoor activity
bifocals and progressive lenses

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17
Q

Management of myopia

A 
spherical concave lenses to diverge light
keratorefractive surgery (ablation of central corneal curvature)
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18
Q

What factors can cause hypermetropia?

A

axial length <24mm

refractive power too week e.g. aphakik patients

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19
Q

What complications can occur as a result of hypermetropia?

A 
accommodative esotropia
amblyopia
early onset presbyopia
angle closure glaucoma
retinoschisis
uveal effusion syndrome
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20
Q

Management of hypermetropia

A 
spherical convex lenses (plus spheres)
keratorefractive surgery (ablation of peripheral corneal tissue)
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21
Q

formula to calculate power

A

P= 1/focal length

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22
Q

what is astigmatism?

A

power of the eye not the same in all meridians

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23
Q

what is regular astigmatism?

A

meridians at 90 degrees

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24
Q

what is irregular astigmatism?

A

meridians not perpendicular e.g. keratoconus

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25
Q

what lenses can be used to treat astigmatism?

A

toric lenses

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26
Q

What sort of contact lenses can be used to treat astigmatism in keratoconus?

A

rigid lenses

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27
Q

how do cylindrical lenses focus light?

A

in a line

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28
Q

how do you transpose a cylinder lens onto a spherical lens

A

add powers
change the sign
change the axis by 90 degrees

Written as +A DS/ - B DC at 90 degrees

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29
Q

what is presbyopia?

A

loss of accommodation

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30
Q

Describe the image formed by a prism

A

virtual, erect and displaced towards the apex

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31
Q

How is prism power calculated?

A

2 x angle of deviation

lens power x distance (cm from pupil to optic centre

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32
Q

In esotropia, where should the base of the prism lens be placed?

A

temporally

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33
Q

In exotropia, where should the base of the prism be placed?

A

nasally

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34
Q

A snellen score of 6/6 is equal to what on a logmar chart?

A

0

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35
Q

A snellen score of 6/60 is equal to what on a logmar chart?

A

1

36
Q

What is the WHO definition of blindness with regards to a snellen chart?

A

3/60

37
Q

What is the WHO definition of blindness with regards to a logmar chart?

A

1.3

38
Q

what is the most commonly used slit lamp technique?

A

direct illumination

39
Q

What slit lamp technique is used to assess external eye structures?

A

diffuse illumination

40
Q

What slit lamp technique reflects light off the retina and can be use to visualise the iris

A

trans/retroillumination

41
Q

What slit lamp technique is used to visualise the corneal endothelium e.g. Fuch’s corneal dystrophy?

A

specular illumination

42
Q

what slit lamp technique is used to visualise corneal opacities?

A

sclerotic scatter

43
Q

what level of magnification is achieved by direct ophthalmoscopy?

A

15x

44
Q

what sort of image is created by direct ophthalmoscopy?

A

virtual and erect

45
Q

What degree of magnification is achieved by indirect ophthalmoscopy?

A

2-5x

46
Q

What power of lens is generally used for indirect ophthalmoscopy?

A

20D

47
Q

What sort of image is created by indirect ophthalmoscopy?

A

real, horizontally and vertically inverted

48
Q

Does indirect or direct ophthalmoscopy create a larger field of illumination for myopes?

A

indirect

49
Q

Where is the lens capsule thinnest?

A

posteriorly

50
Q

what substances is the lens made of?

A

type 4 collagen and glycosaminoglycans

51
Q

Which side of the lens capsule thickens with age?

A

anterior

52
Q

what shape is the anterior suture?

A

Y

53
Q

What shape is the posterior suture?

A

inverted Y

54
Q

Yellowing of the crystalline lens due to deposition of urochrome pigment. Second sight phenomenon.

A

nuclear sclerotic cataract

55
Q

Wedge shaped opacities with lots of glare

A

cortical cataract

56
Q

Glare, difficulty seeing in bright light, difficulty with near vision.

A

posterior subcapsular cataract

57
Q

polychromatic needle like opacities in the deep cortex and nucleus

A

christmas tree cataract

58
Q

What way do prisms refract light?

A

towards the base

59
Q

How much deviation does one prism dioptre produce

A

1cm at 1m

60
Q

True or false, prism power should be divided equally between the two eyes

A

true

61
Q

What is the critical angle?

A

angle of incidence when angle of refraction is 90 degrees

62
Q

When does total internal reflection occur?

A

when angle of incidence > critical angle

63
Q

What sort of cataract forms after blunt trauma?

A

flower shaped

64
Q

What sort of cataract is associated with atopic dermatitis?

A

shield like

65
Q

What sort of cataract is associated with Wilson’s disease?

A

Sunflower

66
Q

What condition causes glaukomflecken cataract?

A

post congestive angle closure glaucoma

67
Q

what drug is associated with bilateral cataract formation?

A

steroids

68
Q

What sort of cataract is associated with diabetes?

A

snowflake

69
Q

What condition is associated with christmas tree cataracts?

A

myotonic dystrophy

70
Q

What infection is associated with pearly nuclear sclerotic cataracts?

A

rubella

71
Q

What sort of cataract is associated with Down’s sydrome?

A

blue dot

72
Q

What sort of cataract is associated with hypoparathyroidism?

A

polychromatic cataract

73
Q

what is the gold standard of management for cataracts?

A

phacoemulsification

74
Q

What are the benefits of phacoemulsification compared to ECCE?

A

smaller incision
less astigmatism
faster recovery
less wound infection

75
Q

What are the disadvantages of phacoemulsification compared to ECCE?

A

hard to learn
expensive equipment
difficult to perform on hard lens

76
Q

what sort of IOL replacement is most commonly used?

A

acrylic hydrophobic IOL

77
Q

what is one side effect of acrylic hydrophobic IOL?

A

dysphotopsia (troublesome glare)

78
Q

What is one side effect of acrylic hydrophilic IOL?

A

posterior capsule opacification

79
Q

What are the three main complications of cataract surgery?

A 
Irvine Gass (CMO)
Posterior capsule opacification 
endophthalmitis
80
Q

Post cataract surgery. Gradual vision loss. Elschnig pearls (grape like, swollen lens epithelial cells), sommering rings.

A

posterior capsule opacification due to posterior migration of lens epithelial cells

81
Q

What is the main causative organism in post cataract surgery endophthalmitis?

A

staph aureus

82
Q

What topical treatment should be given pre-operatively to prevent endophthalmitis?

A

povidone-iodine 5%

83
Q

What is the main causative organism in delayed endophthalmitis post cataract surgery?

A

p. acnes

84
Q

Immunocompromised patient with endophthalmitis. Puff cells present. What is the causative organism?

A

candida

85
Q

Which organism causing post trauma endophthalmitis has the worst prognosis?

A

bacillus cereus

Duke Elder (8 decks)

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