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Duke Elder 2020 > Lens and Cataracts > Flashcards

Lens and Cataracts Flashcards

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
Q

What cataracts does myotonic dystrophy cause?

A

christmas tree like cataracts

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26
Q

What cataract does rubella cause?

A

pearly nuclear sclerotic

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27
Q

What cataract does down syndorme cause

A

Blue dot

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28
Q

What cataract does hypoparathyroidism cause?

A

polychromatic cataract

29
Q

What is the gold standard for cataract Tx?

A

replacement of the lens with a new intraocular lens

phacoemulsification is gold std

30
Q

How does phacoemulsification work?

A

uses an ultrasonically driven needle to chop nucleus and then aspirate lens

31
Q

how does extracapsular cataract extraction work?

A

may be used for very hard cataracts

32
Q

What are the advantages of phacoemulsification vs ECCE?

A

smaller incision

less astigmatism

faster recovery

reduced complications

no sutures required

33
Q

How is the power of the IOL calculated?

A

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
Q

What are the two types of IOLs?

A

rigid and flexible

35
Q

describe rigid IOLs

A

made of polymethylmethacrylate (PMMA)

larger incision

higher rates of posterior capsular opacification than flexible IOL

36
Q

Describe flexible IOLs

A

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
Q

What are some intraoperative complications of cataract surgery?

A

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
Q

What are some post operative complications of cataract surgery?

A

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
Q

What is endophthalmitis?

A

inflammation of the vitreous and aqueous humour usually caused by infection

characterised by progressive vitiritis

40
Q

how is endophthalmitis prevented?

A

povidone-iodine 5% antiseptic to clean eyes perioperatively

41
Q

What are the features of endophthalmitis?

A

vitritis (floaters and blurred vision)

pain

hypopyon

corneal haze

42
Q

How is endophthalmitis managed?

A

intravitreal antiobiotics or pars plana vitrectomy

43
Q

What did the early vitrectomy study gorup find?

A

early vitrectomy is only beneifical in patients with light-perception only vision

44
Q

What is acute endophthalmitis?

A

usually occurs within first week of surgery

due to patients own’ periocular flora,

STAPH EPIDERMIS

45
Q

What is delayed endophthalmitis?

A

between 6 weeks to several months

PROPIONIBACTERIUM ACNES

46
Q

What are some other causes of endophthalmitis?

A

post trauma: staphylococcus or Bacillus cereus (worst prog)

Fungal: candida: occurs in immunocompromised patients most common cause of endogenous endophthalmitis

47
Q

What is the most common complication of late cataract surgery?

A

posterior capsule opacification, due to posterior migration of lens epithelial cells

48
Q

What are the features of posterior capsule pacification?

A

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
Q

How is posterior capsule opacification managed?

A

Nd: YAG laser

50
Q

Describe the inheritence of bilateral congenital cataracts

A

AD

51
Q

describe the inheritence of unilateral congenital cataracts

A

sporadic

52
Q

What are some secondary causes of congenital cataracts?

A

galactosaemia

lowe syndrome

fabry disease

mannosidosis

down syndrome

TORCH intrauterine infection

53
Q

Describe galactosaemia

A

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
Q

What is low syndrome?

A

XLR condition

due to abnormality in amino acid metabolism

features: seizures, cataracts, posterior lenticonus congenital glaucoma

55
Q

What is fabry disease?

A

spoke shaped posterior cataracts and corneal verticillata

56
Q

What is mannisidosis?

A

AR condition due to deficiency in alpha mannosidase

spoke shaped posterior cataracts

57
Q

What are the torch infections?

A 
toxoplasmosis 
other (VZV, synphilis, parvovirus b19) 
rubella 
cmv
HSV
58
Q

What is the management for congenital cataracts?

A

observation if small, < 3mm and partial dense

unilateral: part time occlusion, pharmacological mydriasis of good eye can help prevent amblyopia (delays cataract surgery)

59
Q

What is the surgery for congenital cataracts?

A

pars plana lensectomy, posterior capsule capsulorhexis and anterior vitrectomy where appropriate

60
Q

how is a bilateral dense congenital cataract treated?

A

treat within 8-10 weeks

61
Q

How is a unilateral dense cataract treated?

A

surgical treatment within 6 weeks due to higher risk of amblyopia

62
Q

What are some post operative complications of managing congenital cataracts?

A

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
Q

What is anterior lenticonus?

A

bilateral thinning of the anterior capsule with anterior lens protrusion into the anterior chamber

associated with alport syndrome (type IV collagen disorder)

64
Q

What is posterior lenticonus?

A

deformity in the posterior surgace of the lens that is usually unilateral

associated with congenital cataract

associated with lowe syndrome

65
Q

What is ectopia lentis?

A

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
Q

What are some ocular causes of ectopia lentis?

A

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
Q

What are some systemic causes of ectopia lentis?

A

marfan syndrome

68
Q

Describe marfan syndrome

A

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
Q

What is homocystinuria?

A

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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