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Duke Elder 2020 > Lens and Cataracts > Flashcards

Lens and Cataracts Flashcards

(69 cards)

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1
Q

Where is the lens located?

A

between iris and vitreous

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2
Q

What is the power of the lens in adults?

A

15-20D

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3
Q

What is the power of the lens in infancy?

A

43-47D

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4
Q

What is the refractive index of the lens?

A

1.4

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5
Q

How does near accomodation work?

A

Ciliary muscle contraction - zonule relaxation - lens becomes more spherical and increases dioptre power

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6
Q

How does far accommodation work?

A

Ciliary muscle relaxation - increases zonular tension and lens becomes flat

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7
Q

Describe the histology of the capsule

A

outer transparent basement membrane

thinnest posteriorly and thickest near the equators

made of type IV collagen and glycosaminoglycan

anterior capsule THICKENS WITH AGE, posterior remains the same

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8
Q

Describe the histology of the lens epithelium

A

simple cuboidal cells below capsule

central zone: present on the anterior surface of the lens

pre-equatorial zone: cells undergo mitotic division through life and form the lens fibres

no epithelium on the posterior surface of the lens

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9
Q

Describe the histology of lens fibres

A

elongate and push older fibres deeper into the lens

nucleus is innermost part, present at birth

cortex = youngest part, outer part

junction of lens forms sutures:

  • anterior suture: upright Y shaped suture
  • posterior suture: inverted y shaped suture
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10
Q

What are zonules?

A

suspensory ligaments made of fibrillin, attached to the lens equator

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11
Q

What is a cataract?

A

progressive cloudiness of the lens causing gradual vision loss and blindness if untreated

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12
Q

What is the leading cause of blindness worldwide?

A

cataracts

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13
Q

Describe the grading of cataracts

A

immature: partially opaque
mature: completely opaque

Hypermature cataract: shrunken anterior capsule due to leakage of material outside the lens

morganian cataract: a form of hypermature cataract with cortex liquefaction causing the nucleus to sink

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14
Q

What are some complications of a morganian cataract?

A

phacoanaphylactic uveitis and phacolytic glaucoma

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15
Q

Describe nuclear sclerotic cataracts

A

characterised by yellowing of the crystalline lens due to deposition of the urochrome pigment

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16
Q

What phenomenon may be seen in nuclear sclerotic cataracts?

A

‘second sight’ elderly patients able to see close again

lens becomes harder, refractive index increases

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17
Q

Describe cortical cataracts

A

occur due to opacification of lens cortex

characterised by wedge shaped opacities

glare is the predominant symptoms especially when driving at night

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18
Q

describe the stereotypical nuclear sclerotic cataract pt

A

elderly, suddenly able to read close again

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19
Q

describe the stereotypical cortical cataracts

A

glare when driving especially at night from headlights

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20
Q

Describe subscapular cataracts

A

anterior subscapular: opacities under the anterior capsule

posterior subscapular: opacities under the posterior capsule, glare is a common symptom, difficult seeing in bright light and near vision

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21
Q

Describe polychromatic cataracts

A

characterised y needle-like opacities in the deep cortex and nucleus

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22
Q

What are the age related cataracts categorised into?

A

nuclear, cortical, subcapsular and polychromatic

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23
Q

What can cause acquired anterior subcapsular cataracts?

A

blunt trauma (flower shaped cataract)

atopic dermatitis (shield-like cataracts)

Wilson’s disease (sunflower cataracts)

post PACG - glaukomflecken

gold (drug induced)

infrared radiation (glass blower cataracts)

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24
Q

What can cause posterior subcapsular cataracts?

A

corticosteroids

diabetes (snowflake shaped cataracts)

retinitis pigmentosa

NF2

Chloroquine

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25
What cataracts does myotonic dystrophy cause?
christmas tree like cataracts
26
What cataract does rubella cause?
pearly nuclear sclerotic
27
What cataract does down syndorme cause
Blue dot
28
What cataract does hypoparathyroidism cause?
polychromatic cataract
29
What is the gold standard for cataract Tx?
replacement of the lens with a new intraocular lens phacoemulsification is gold std
30
How does phacoemulsification work?
uses an ultrasonically driven needle to chop nucleus and then aspirate lens
31
how does extracapsular cataract extraction work?
may be used for very hard cataracts
32
What are the advantages of phacoemulsification vs ECCE?
smaller incision less astigmatism faster recovery reduced complications no sutures required
33
How is the power of the IOL calculated?
P = A -2.5L - 0.9K A is manufacturers constant l is axial length measured using a-scan ultrasonography k is average corneal power
34
What are the two types of IOLs?
rigid and flexible
35
describe rigid IOLs
made of polymethylmethacrylate (PMMA) larger incision higher rates of posterior capsular opacification than flexible IOL
36
Describe flexible IOLs
used in modern cataract surery acrylic hydrophobic IOL: higher refractive index and lower rates of post caps opc than hydrophilic, can cause dysphotopsia acrylic hydrophilic IOL: higher biocompatibility, but lens calcification may occur silicone: less commonly used in modern phacoemulsification
37
What are some intraoperative complications of cataract surgery?
posterior lens capsule rupture floppy iris sydrome: a flaccid iris that can complicate surgery, occurs in some patients on alpha blockers (use intracameral phenylephrine to dilate pupils)
38
What are some post operative complications of cataract surgery?
early: corneal oedema, elevated IOP and acute endophthalmitis late: PCO, irvine gass syndrome (CMO post cataract surgery), retinal detachment (especially if high myopia)) and delayed endophthalmitis
39
What is endophthalmitis?
inflammation of the vitreous and aqueous humour usually caused by infection characterised by progressive vitiritis
40
how is endophthalmitis prevented?
povidone-iodine 5% antiseptic to clean eyes perioperatively
41
What are the features of endophthalmitis?
vitritis (floaters and blurred vision) pain hypopyon corneal haze
42
How is endophthalmitis managed?
intravitreal antiobiotics or pars plana vitrectomy
43
What did the early vitrectomy study gorup find?
early vitrectomy is only beneifical in patients with light-perception only vision
44
What is acute endophthalmitis?
usually occurs within first week of surgery due to patients own' periocular flora, STAPH EPIDERMIS
45
What is delayed endophthalmitis?
between 6 weeks to several months PROPIONIBACTERIUM ACNES
46
What are some other causes of endophthalmitis?
post trauma: staphylococcus or Bacillus cereus (worst prog) Fungal: candida: occurs in immunocompromised patients most common cause of endogenous endophthalmitis
47
What is the most common complication of late cataract surgery?
posterior capsule opacification, due to posterior migration of lens epithelial cells
48
What are the features of posterior capsule pacification?
gradual loss of vision and glare, patients may think cataract has recurred Elschnig pearls: grape like collection of swollen lens epithelial cells simmering rings: white annular proliferation of residual cells
49
How is posterior capsule opacification managed?
Nd: YAG laser
50
Describe the inheritence of bilateral congenital cataracts
AD
51
describe the inheritence of unilateral congenital cataracts
sporadic
52
What are some secondary causes of congenital cataracts?
galactosaemia lowe syndrome fabry disease mannosidosis down syndrome TORCH intrauterine infection
53
Describe galactosaemia
AR conditon due to absence of galactose-1-phosphate uridyltransferase features: infant with liver dysfunction, failure to thrive and OIL DROPLET CATARACT Ix: stool for reducing substances Mx: dietary restriction of lactose and galactose
54
What is low syndrome?
XLR condition due to abnormality in amino acid metabolism features: seizures, cataracts, posterior lenticonus congenital glaucoma
55
What is fabry disease?
spoke shaped posterior cataracts and corneal verticillata
56
What is mannisidosis?
AR condition due to deficiency in alpha mannosidase spoke shaped posterior cataracts
57
What are the torch infections?
``` toxoplasmosis other (VZV, synphilis, parvovirus b19) rubella cmv HSV ```
58
What is the management for congenital cataracts?
observation if small, < 3mm and partial dense unilateral: part time occlusion, pharmacological mydriasis of good eye can help prevent amblyopia (delays cataract surgery)
59
What is the surgery for congenital cataracts?
pars plana lensectomy, posterior capsule capsulorhexis and anterior vitrectomy where appropriate
60
how is a bilateral dense congenital cataract treated?
treat within 8-10 weeks
61
How is a unilateral dense cataract treated?
surgical treatment within 6 weeks due to higher risk of amblyopia
62
What are some post operative complications of managing congenital cataracts?
PCO - can lead to ambylopia secondary glaucoma: open angle glaucoma, can occur years after surgery, closed angle may occur immediately post op endophthalmitis retinal detachment
63
What is anterior lenticonus?
bilateral thinning of the anterior capsule with anterior lens protrusion into the anterior chamber associated with alport syndrome (type IV collagen disorder)
64
What is posterior lenticonus?
deformity in the posterior surgace of the lens that is usually unilateral associated with congenital cataract associated with lowe syndrome
65
What is ectopia lentis?
ectopia lentis refers to the dislocation / displacement of the lens from its normal position most common cause is trauma, can be associated with ocular or systemic disease
66
What are some ocular causes of ectopia lentis?
simple (familial) ectopia lentis - occurs congeitally or later in life - AD or AR - Bilateral symmetric lens dislocation superotemporally pseudoexfolation syndrome hypermature cataracts high myopia
67
What are some systemic causes of ectopia lentis?
marfan syndrome
68
Describe marfan syndrome
most common inherited cause of ectopia lentis AD due to mutations in fibrillin-1 gene on chromosome 15 (FBN1 gene) bilateral superotemporal lens dislocation accommodation is not affected because zonules are intact ectopia lentis is most common ocular feature systemic features: tall stature, typically with dolichostenomelia (long limbs), mitral prolapse, aortic aneurysm, regurgitation and dissection and kyphoscoliosis
69
What is homocystinuria?
the second most common inherited cause of ectopia lentis inheritance is AR due to cystathionine beta-synthase deficiency bilateral inferonasal lens dislocation is typical systemic features: coarse blond hair, malar flush, blue irides and intellectual disability

Duke Elder 2020 (9 decks)

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