Lens, cataracts and optics Flashcards
1
Q
What is the refractive power of the lens?
A
20D
2
Q
What is the refractive power of the lens?
A
20D
3
Q
Axial length of the eye in:
a) newborn
b) child
c) adult
A
a) 16mm
b) 22.5mm
c) 24mm
4
Q
What is the length from the lens to the retina in adults?
A
17mm
5
Q
What is the most common cause of myopia?
A
axial length >24mm
6
Q
What conditions increase the power of the eye?
A
keratoconus
nuclear sclerotic cataract
7
Q
What is high myopia?
A
> -6
8
Q
Management of myopia
A
spherical concave lenses to diverge light (minus spheres) keratorefractive surgery (ablation of central corneal curvature)
9
Q
Management of myopia
A
spherical concave lenses to diverge light keratorefractive surgery (ablation of central corneal curvature)
10
Q
What factors can cause hypermetropia?
A
axial length <24mm
refractive power too week e.g. aphakik patients
11
Q
Axial length of the eye in:
a) newborn
b) child
c) adult
A
a) 16mm
b) 22.5mm
c) 24mm
12
Q
What is the length from the lens to the retina in adults?
A
17mm
13
Q
What is the most common cause of myopia?
A
axial length >24mm
14
Q
What conditions increase the power of the eye?
A
keratoconus
nuclear sclerotic cataract
15
Q
What is high myopia?
A
16
Q
What can be done to prevent myopia?
A
atropine and pirenzipine drops
outdoor activity
bifocals and progressive lenses
17
Q
Management of myopia
A
spherical concave lenses to diverge light keratorefractive surgery (ablation of central corneal curvature)
18
Q
What factors can cause hypermetropia?
A
axial length <24mm
refractive power too week e.g. aphakik patients
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
20
Q
Management of hypermetropia
A
spherical convex lenses (plus spheres) keratorefractive surgery (ablation of peripheral corneal tissue)
21
Q
formula to calculate power
A
P= 1/focal length
22
Q
what is astigmatism?
A
power of the eye not the same in all meridians
23
Q
what is regular astigmatism?
A
meridians at 90 degrees
24
Q
what is irregular astigmatism?
A
meridians not perpendicular e.g. keratoconus
25
what lenses can be used to treat astigmatism?
toric lenses
26
What sort of contact lenses can be used to treat astigmatism in keratoconus?
rigid lenses
27
how do cylindrical lenses focus light?
in a line
28
how do you transpose a cylinder lens onto a spherical lens
add powers
change the sign
change the axis by 90 degrees
Written as +A DS/ - B DC at 90 degrees
29
what is presbyopia?
loss of accommodation
30
Describe the image formed by a prism
virtual, erect and displaced towards the apex
31
How is prism power calculated?
2 x angle of deviation
| lens power x distance (cm from pupil to optic centre
32
In esotropia, where should the base of the prism lens be placed?
temporally
33
In exotropia, where should the base of the prism be placed?
nasally
34
A snellen score of 6/6 is equal to what on a logmar chart?
0
35
A snellen score of 6/60 is equal to what on a logmar chart?
1
36
What is the WHO definition of blindness with regards to a snellen chart?
3/60
37
What is the WHO definition of blindness with regards to a logmar chart?
1.3
38
what is the most commonly used slit lamp technique?
direct illumination
39
What slit lamp technique is used to assess external eye structures?
diffuse illumination
40
What slit lamp technique reflects light off the retina and can be use to visualise the iris
trans/retroillumination
41
What slit lamp technique is used to visualise the corneal endothelium e.g. Fuch's corneal dystrophy?
specular illumination
42
what slit lamp technique is used to visualise corneal opacities?
sclerotic scatter
43
what level of magnification is achieved by direct ophthalmoscopy?
15x
44
what sort of image is created by direct ophthalmoscopy?
virtual and erect
45
What degree of magnification is achieved by indirect ophthalmoscopy?
2-5x
46
What power of lens is generally used for indirect ophthalmoscopy?
20D
47
What sort of image is created by indirect ophthalmoscopy?
real, horizontally and vertically inverted
48
Does indirect or direct ophthalmoscopy create a larger field of illumination for myopes?
indirect
49
Where is the lens capsule thinnest?
posteriorly
50
what substances is the lens made of?
type 4 collagen and glycosaminoglycans
51
Which side of the lens capsule thickens with age?
anterior
52
what shape is the anterior suture?
Y
53
What shape is the posterior suture?
inverted Y
54
Yellowing of the crystalline lens due to deposition of urochrome pigment. Second sight phenomenon.
nuclear sclerotic cataract
55
Wedge shaped opacities with lots of glare
cortical cataract
56
Glare, difficulty seeing in bright light, difficulty with near vision.
posterior subcapsular cataract
57
polychromatic needle like opacities in the deep cortex and nucleus
christmas tree cataract
58
What way do prisms refract light?
towards the base
59
How much deviation does one prism dioptre produce
1cm at 1m
60
True or false, prism power should be divided equally between the two eyes
true
61
What is the critical angle?
angle of incidence when angle of refraction is 90 degrees
62
When does total internal reflection occur?
when angle of incidence > critical angle
63
What sort of cataract forms after blunt trauma?
flower shaped
64
What sort of cataract is associated with atopic dermatitis?
shield like
65
What sort of cataract is associated with Wilson's disease?
Sunflower
66
What condition causes glaukomflecken cataract?
post congestive angle closure glaucoma
67
what drug is associated with bilateral cataract formation?
steroids
68
What sort of cataract is associated with diabetes?
snowflake
69
What condition is associated with christmas tree cataracts?
myotonic dystrophy
70
What infection is associated with pearly nuclear sclerotic cataracts?
rubella
71
What sort of cataract is associated with Down's sydrome?
blue dot
72
What sort of cataract is associated with hypoparathyroidism?
polychromatic cataract
73
what is the gold standard of management for cataracts?
phacoemulsification
74
What are the benefits of phacoemulsification compared to ECCE?
smaller incision
less astigmatism
faster recovery
less wound infection
75
What are the disadvantages of phacoemulsification compared to ECCE?
hard to learn
expensive equipment
difficult to perform on hard lens
76
what sort of IOL replacement is most commonly used?
acrylic hydrophobic IOL
77
what is one side effect of acrylic hydrophobic IOL?
dysphotopsia (troublesome glare)
78
What is one side effect of acrylic hydrophilic IOL?
posterior capsule opacification
79
What are the three main complications of cataract surgery?
```
Irvine Gass (CMO)
Posterior capsule opacification
endophthalmitis
```
80
Post cataract surgery. Gradual vision loss. Elschnig pearls (grape like, swollen lens epithelial cells), sommering rings.
posterior capsule opacification due to posterior migration of lens epithelial cells
81
What is the main causative organism in post cataract surgery endophthalmitis?
staph aureus
82
What topical treatment should be given pre-operatively to prevent endophthalmitis?
povidone-iodine 5%
83
What is the main causative organism in delayed endophthalmitis post cataract surgery?
p. acnes
84
Immunocompromised patient with endophthalmitis. Puff cells present. What is the causative organism?
candida
85
Which organism causing post trauma endophthalmitis has the worst prognosis?
bacillus cereus
