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lens and cataracts Flashcards

1
Q

define lens

A

lens is a biconvex crystalline structure located between the iris and vitreous. It has a power of 15–20D in adults and 43–47D in infancy. Its high-protein (crystalline) content gives the lens a high refractive index of about 1.4.

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2
Q

what happens at near accomodation

A

The eye brings near objects into focus by contracting the ciliary muscle. This results in the relaxation of the zonules making the lens more spherical and increasing its diopter power.

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3
Q

what happens at far accomodation

A

The eye brings far objects into focus by relaxing the ciliary muscle. This increases zonular tension, making the lens flat.

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4
Q

histology of capsule cataract

A

● An outer transparent basement membrane.
● Thinnest posteriorly and thickest near the equators.
● Made of type IV collagen and glycosaminoglycan.
● Anterior capsule thickens with age, but the posterior capsule maintains the
same thickness.

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5
Q

histology of epithelium cataracts

A

● Simple cuboidal cells located beneath the capsule.
● Central zone: Present on the anterior surface of the lens.
● Pre-equatorial zone: Cells undergo mitotic division throughout life and form
the lens fibres.
● No epithelium on the posterior surface of the lens.

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6
Q

histology of lens fibres cataracts

A

● Lens fibres elongate, pushing the older fibres deeper into the lens.
● The nucleus is the innermost part, which is present at birth, and the cortex is
the outer part, which contains the youngest fibres.
● The junction of lens fibres forms sutures:
Anterior suture: Has an upright Y-shaped suture. Posterior suture: Has an inverted Y-shaped suture.

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7
Q

histology of zonules cataracts

A

Suspensory ligaments, made of fibrillin, attached to the lens equator.

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8
Q

what is cataract maturity

A

progressive cloudiness of the lens causing gradual vision loss and blindness if untreated. It is the leading cause of blindness worldwide.

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9
Q

grading of cataracts

A

● Immature cataract: Partially opaque.
● Mature cataract: Completely opaque.
● Hypermature cataract: Shrunken anterior capsule due to leakage of material/water outside the lens.
● Morgagnian cataract: A form of hypermature cataract with cortex
liquefaction causing the nucleus to sink. Complications include phacoanaphylactic uveitis and phacolytic glaucoma.

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10
Q

classification of age-related cataracts

A

nuclear, cortical, subcapsular and polychromatic cataracts.

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11
Q

what is nuclear sclerotic
signs
patho

A

EARLY - yellowing of the crystalline lens due to the deposition of the urochrome pigment.

LATE - brown

increase in refractive index of the nucleus and increased spherical abberation- myopic shift leading to ‘second sight’ phenomenon

lens becoming harder, the refractive index increases, allowing for some elderly patients to read without glasses.

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12
Q

what is cortical cataracts

A

opacities start as clefts and vacuoles between lens fibres due to hydration of the cortex.

Subsequently opacification results in typical cuneiform (wedge-shaped) or radial spoke-like opacities
opacification of the lens cortex.

wedge-shaped opacities

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13
Q

predominant Sx of cortical cataracts

A

glare - especially from headlights while driving at night.

this is due to light scattering

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14
Q

anterior subcapsular cataract

A

opacities under the anterior capsule

under the lens capsule and ass w fibrous metaplasia of the lens epithelium

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15
Q

posterior subcapsular cataract

A

Opacities just in front of the posterior capsule. Glare is acommon symptom.

vacuolated , granular or plaque-like appearance on oblique slit lamp biomicroscopy

black on reteroillumination

Patients may complain of difficulty seeing in bright light and near vision.

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16
Q

description of polychromatic ‘xmas tree’ cataract

A

Characterized by needle-like opacities in the deep cortex and nucleus

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17
Q

acquired anterior subcapsular cataracts examples and their ass

● Blunt trauma 
● Atopic dermatitis
 ● Wilson disease 
● Post-congestive angle closure glaucoma 
● Gold 
● Infrared radiation
A

● Blunt trauma (flower-shaped cataract)
● Atopic dermatitis (shield-like cataract)
● Wilson disease (sunflower cataract)
● Post-congestive angle closure glaucoma (glaukomflecken)
● Gold (drug induced)
● Infrared radiation (glass-blower cataract)

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18
Q

posterior subcapsular cataracts examples and their ass

A 
● Corticosteroids
● Diabetes (snowflake shaped)
● Retinitis pigmentos
● NF2
● Chloroquine
- myotonic dystrophy - stellate
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19
Q 
other cataracts
myotonic dystrophy
rubella
down syndrome
hypoparathyroidism
A

● Christmas tree-like cataract appearance: Myotonic dystrophy
● Pearly nuclear sclerotic cataract: Rubella
● Blue dot cataract: Down syndrome
● Polychromatic cataract: Hypoparathyroidism

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20
Q

Gold standard Mx for cataracts

A

phacoemulsification

This technique uses an ultrasonically driven needle (phaco tip) to chop the nucleus and then aspirate the lens material.

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21
Q

other type of Mx for cataracts

A

Extracapsular cataract extraction (ECCE): May be used for very hard cataracts.

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22
Q

advantages of phacoemulsification

A 
● Smaller incision
● Less astigmatism
● Faster recovery
● Reduced complications
● No sutures needed
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23
Q

what is intraocular lens power

A

IOL power is determined by measuring the curvature of the cornea and eye length. Power (P) is calculated using the following equation:
P = A − 2.5L − 0.9K

where:
● A is a constant supplied by the manufacturer.
● L is the axial length of the eye, measured using A-scan ultrasonography.
● K is the average corneal power reading in diopters.

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24
Q

what is rigid IOL

A

● Made of polymethylmethacrylate (PMMA).
● Requires a larger incision. more than 5mm
● Higher rates of posterior capsular opacification (PCO) than flexible IOL.

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25
Q

what is flexible IOL

types

A

● Used in modern cataract surgery.
- smaller incision
● Three types

Acrylic hydrophobic IOL: Has a higher refractive index and lower rates of PCO than its hydrophilic counterparts. However, can cause dysphotopsia (troublesome glare). greater reaction in uveitic eyes

Acrylic hydrophilic IOL: Has higher biocompatibility. However, calcification of the lens (causing lens opacities) may occur. better with uveitic eyes

Silicone IOL: Less commonly used in modern phacoemulsification.

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26
Q

complications of intraoperative surgery

A
  • Posterior lens capsule rupture.
  • Floppy iris syndrome: A flaccid iris that can complicate surgery. It usually occurs with some patients on alpha blockers (e.g. tamsulosin). Intracameral phenylephrine can be used to dilate pupils in high risk patients
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27
Q

complications of postoperative surgery

A

Early: Corneal oedema, elevated IOP and acute endophthalmitis.

Late: PCO (most common complication), Irvine-Gass syndrome (CMO post cataract surgery), retinal detachment (especially in patients with high myopia) and delayed endophthalmitis.

28
Q

what is endopthalmitis

A

inflammation of the vitreous and aqueous humour, usually caused by infection. It is characterized by progressive vitritis.

staph epidermidis is common

29
Q

main prevention of endopthalmitis

A

povidone-iodine 5% antiseptic

prophylatic ABx

30
Q

features of endopthalmitis

A

Progressive vitritis (blurred vision, floaters), pain, hypopyon and corneal haze.

31
Q

Mx of infective endophthalmitis

A

Intravitreal antibiotics ie ceftazidime - gram negative and vancomycin - coagulase negative or

pars plana vitrectomy.

In acute endophthalmitis, the Early Vitrectomy Study Group found that early vitrectomy is only beneficial in patients with light perception-only vision

32
Q

what is acute endophthalmitis

A

● Usually occurs within the first week of surgery.
● This is due to the patient’s own periocular flora. The main causative
organism is Staphylococcus epidermidis.

Most common source: bacteria from patient’s lids/conjunctiva

33
Q

what is delayed endopthalmitis

features

A

● Onset varies from 6 weeks to several months.
● Main causative organism is Propionibacterium acnes.
• Indolent uveitis/vitritis
• White capsular plaque, painless

34
Q

other causes of endophthalmitis

A

● Post-trauma: Staphylococcus or Bacillus cereus (has the worst prognosis).
● Fungal (Candida): Occurs in immunocompromised patients. Most common
cause of endogenous endophthalmitis.

35
Q

most common complication of late cataract surgery

A

posterior capsular opacification

36
Q

what is posterior capsular opacification

A

The posterior capsule opacifies due to posterior migration of lens epithelial cells.

37
Q

features of posterior capsular opacification

A

● Gradual loss of vision and glare; patients often think their cataracts have recurred.
- capsular fibrosis
● Elschnig pearls: Grape-like collection of swollen lens epithelial cells - proliferation of epithelial cells in the posterior capsule which usually has none
● Sommering rings: White annular proliferation of residual cells.

38
Q

Mx of posterior capsular opacification

A

Capsulotomy with Nd:YAG laser.

39
Q

secondary causes of congenital cataracts

A

galactosaemia

lowe syndrome

fabry disease

mannosidosis

down

TORCH

40
Q

what is galactosaemia

features

Ix
Mx

A
  • AR condition due to absence of galactose-1-phosphate uridyltransferase.
  • Features: Infant presenting with liver dysfunction, failure to thrive and oil-droplet cataract.

Investigation: Stool for reducing substances.

Management: Dietary restriction of lactose and galactose.

41
Q

what is lowe syndrome

A

XLR condition due to an abnormality in amino acid metabolism.

Features: Seizures, cataracts, posterior lenticonus and congenital glaucoma.

42
Q

what is fabry disease

A

XL lysosomal storage disorder

periodic burning pain in extremities, telangectasias
Spoke-shaped posterior cataracts and corneal verticillata.

43
Q

what is mannosidosis

inheritance

feature

A

AR condition due to deficiency in alpha mannosidase.

Spoke-shaped posterior cataracts.

44
Q

features of down syndrome

A

Single palmar crease, low set ears, large tongue, epicanthal folds and blue dot cataract.

45
Q

what is TORCH

A

Toxoplasmosis, other (VZV, syphilis, parvovirus B19), rubella, CMV, HSV.

46
Q

Mx of congenital cataracts

A

● Observation, for small, <3 mm diameter, partial dense cataracts.
● In unilateral cases, part-time occlusion or pharmacological mydriasis of the
good eye can be helpful to avoid amblyopia. These interventions are useful in delaying the need for cataract surgery until the eye growth becomes stable.
● Surgery: Involves pars plana lensectomy, posterior capsule capsulorhexis and anterior vitrectomy where appropriate. In addition to correction of refractive errors.
● A bilateral dense cataract requires surgical treatment within 8–10 weeks.
● A unilateral dense cataract requires surgical treatment within 6 weeks due to
a higher risk of amblyopia.

47
Q

postop complications of congential cataracts

A
  1. Posterior Capsular Opacification: A dangerous complication, as it can lead to amblyopia.
  2. Secondary glaucoma: Open-angle glaucoma can occur years after surgery. Angle closure may occur immediately postop. Incidence is higher if surgical treatment was performed within the first month of life.
  3. Endophthalmitis.
  4. Retinal detachment.
48
Q

what is anterior lenticonus

A

Bilateral thinning of the anterior capsule with anterior lens protrusion into the anterior chamber.

  • Alport syndrome (type IV collagen mutation disorder).
  • AD
  • sensorineural deafness and renal disease
49
Q

what is posterior lenticonus

A

Deformity in the posterior surface of the lens that is usually unilateral. Associated with congenital cataract. Associated with Lowe syndrome.

50
Q

what is ectopia lentis

A

dislocation/displacement of the lens from its normal position. The most common cause is trauma

51
Q

ocular causes of ectopia lentia

A 
● Simple (familial) ectopia lentis
Occurs congenitally or later in life
Inheritance: AD or AR
Bilateral symmetric lens dislocation superotemporally
● Pseudoexfoliation syndrome
● Hypermature cataracts
● High myopia
52
Q

systemic causes of ectopia lentis

A

marfan

homocystinuria

53
Q

marfan syndrome causing ectopia lentis

A

● Most common inherited cause of ectopia lentis.
● Inheritance: AD due to mutations of fibrillin-1 gene on chromosome 15
(FBN1 gene).
● Bilateral superotemporal lens dislocation is typical. Accommodation is not affected because ZONULES ARE NOT BROKEN
● Systemic features
- Tall stature, typically with dolichostenomelia (unusually long limbs) - Mitral prolapse, aortic aneurysm, regurgitation and dissection
- Kyphoscoliosis

54
Q

homocystinuria causing ectopia lentis

A

● The second most common inherited cause of ectopia lentis.
● Inheritance: AR due to cystathionine beta-synthase deficiency.
● Bilateral inferonasal lens dislocation is typical.
- ZONULES BROKEN
Skeletal abnormalities, mental disability, risk of thrombotic complications (especially with anaesthesia)

● Systemic features

  • Coarse blond hair
  • Malar flush
  • Blue irides
  • Intellectual disability

• Treatment of homocystinuria: low methionine, high cysteine diet

55
Q

nuclear sclerotic cataract is assessed by

A

oblique slit-lamp biomicroscopy and not by retroillumination

56
Q

secondary cataracts - cataracts that develope as a result of some other primary ocular disease

A

anterior uveiits
acute agnle closure glaucoma
hereditary fundus dystrophies

57
Q

drugs associated with cataracts

A
  • Steroids
  • Chropromazine • Gold
  • Amiodarone
  • Busulphan
  • Allopurinol
58
Q

anaesthetic options

A

sub-tenon block - 5mm from limbus into subtenon space - akinesia is variable

peribulbar block - akinesia and anaesthesia good but perforation of eyeball is risky

topical anaesthesia - absent akinesia

59
Q

signs of ruptured posterior lens capsule

A

sudden shallowing of AC

60
Q

presentation of delayed onset postop endophthalmitis

A

painless visiual deterioration ass w floaters

mutton fat keratic precipitates

61
Q

anterior stellate cataract

A

phenothiazine, amiodarone

62
Q

RFs of cataracts

A

UV exposure, smoking, sugar level, steroid use

63
Q

Mx of delayed endophthalmitis

A

• Difficult eradication (intracameral vancomycin),may require Intraocular lens explant & Capsulectomy (to get rid of the plaque)

64
Q

metabolic causes of ectopia lentis

A

• Abnormal elastin (Marfan’s)
• Metabolism: Homocysteinuria,
Sulfite oxidase, hyperlysinaemia)

65
Q

genetic causes of ectopia lentis

A

• Weil-Marchesani Syndrome - converse of marfan
short stature, bradyactlyy, stubby fingers, ectopia lentis inferior
microsphelakia - subluxation anteriorly

• Pierre Robin syndrome

66
Q 
wilson
mytonic dystrophy
trisomy 21
outdoor exposure
posterior subcapsular cataract
nuclear sclerotic
anterio stellate cataract
A
  • Wilson’s disease = sunflower cataract, which is anterior sub capsular.
  • Myotonic dystrophy = Christmas cataract
  • Trisomy 21 = Cerulean Blue dot cataract
  • Outdoor exposure = cortical cataract
  • Posterior subcapsular cataract = most likely to produce symptoms of glare in bright light
  • Nuclerar sclerotic = myopic shift “able to read the newspaper without wearing glasses again”
  • Anterior stellate cataract: phenothiazine, amiodarone

DEP (20 decks)

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