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Ophthalmology > Lens and Cataracts > Flashcards

Lens and Cataracts Flashcards

1
Q

Describe the shape and structure of the lens

A

The lens is a biconvex crystalline structure located between the iris and the vitreous

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2
Q

What is the power of the lens?

A

15-20D in adults and 43-47D in infancy

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3
Q

What is the refractive index of the lens?

A

1.4

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4
Q

What gives the lens its high refractive index?

A

High-protein (crystalline) structure

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5
Q

What is refractive index?

A

A ratio of the speed of light through a medium as a ratio to its speed through a vacuum

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6
Q

Describe the process of accommodation

A

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

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7
Q

Describe de-accommoation?

A

The eye brings far objects into focus by relaxing the ciliary muscle, increasing zonular tension and making the lens flatter

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8
Q

Describe the structure of the lens

A

Capsule
Epithelium
Lens fibres
Zonules

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9
Q

What is the lens capsule made of?

A

Type IV collagen and glycosaminoglycan

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10
Q

How does the capsule change with age?

A

Anterior capsule thickens with age whereas the posterior doesn’t change.

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11
Q

What is the structure of the epithelium?

A

Simple cuboidal cells located beneath the capsule

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12
Q

The epithelium is separated into zones. Describe them.

A

Central zone - present on the anterior surface of the lens

Pre-equatorial zone - cells undergo mitotic division throughout life to form the lens fibres

There is no epithelium on the posterior surface of the lens

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13
Q

How do lens fibres develop?

A

Elongated fibres push older ones deeper into the lens.

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14
Q

What are the layers of the lens?

A

Nucleus (present at birth) and cortex

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15
Q

The junctions of the lens fibres form anterior and posterior sutures. How do you distinguish them?

A

Anterior suture: Y-shaped

Posterior suture: inverted Y-shape

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16
Q

What are the zonules?

A

Suspensory ligaments made of fibrillar which attach to the lens equator

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17
Q

What is a cataract?

A

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

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18
Q

How are cataracts graded?

A

Immature - partial cloudiness

Mature - total cloudiness

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

Morgagnian - hyper mature with cortex liquefaction (Cx include phacolytic glaucoma)

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19
Q

What is the most common reason for developing cataracts

A

Age-related

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20
Q

List types of age-related cataract

A

Nuclear sclerotic
Cortical
Subcapsular (anterior or posterior)
Polychromatic

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21
Q

Describe a nuclear sclerotic cataract

A

Characterised by the yellowing of the lens due to urochrome pigment deposit.

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22
Q

What is ‘second sight’ phenomena in nuclear sclerotic cataracts?

A

As the lens hardens its refractive index increases and a myopic shift in their refractive error occurs. This can lead some people with hyperopia to read without glasses required.

23
Q

How are cortical cataracts characterised?

A

Opacification of the lens cortex leads to wedge-shaped opacities with glare being the predominant symptom

24
Q

What are the associations with development of anterior subcapsular cataracts?

A

Blunt trauma (flower-shaped cataract)

Atopic dermatitis (shield-like cataract)

Wilson disease (sunflower cataract)

Post-congestive angle closure cataract (glaukomfelcken)

Gold (drug induced)

Infrared radiation (glass-blower cataract)

25
Q

What are the associations with development of posterior subcapsular cataracts?

A 
Corticosteroids 
Diabetes (snowflake shaped)
Retinitis pigmentosa
NF2
Chloroquine
26
Q

List some other types of cataract

A

Christmas tree-like cataract (myotonic dystrophy)

Pearly nuclear sclerotic cataract (Rubella)

Blue dot cataract (Down syndrome)

Polychromatic cataract (hypoparathyroidism)

27
Q

What are the two surgical treatment methods from cataract?

A

Phacoemulsification (gold standard)

Extracapsular cataract extraction (may be used for very hard cataracts)

28
Q

What are the advantages of phacoemulsification over ECCE?

A

Smaller incision

Less astigmatism

Faster recovery

Reduced complications

No sutures needed (most of the time)

29
Q

How is intra-ocular lens power calculated?

A

P = A - 2.5L - 0.9K

Where:

A is the constant supplied by the manufacturer

L is the axial length

K is the average corneal power reading in D

30
Q

What are the two different types of IOL used in cataract surgery?

A

Rigid or flexible IOLs

31
Q

Outline what rigid IOLs are

A

Made of polymethylmethacrylate (PMMA) and requires larger incision and has higher rates of posterior capsule opacification than flexible counterparts

32
Q

What are the three types of flexible IOL?

A

Acrylic hydrophobic - higher refractive index, lower rates of PCO. Can cause dysphotopsia

Acrylic hydrophobic - higher biocompatibility by lens calcification can occur

Silicone: less common

33
Q

List some intraoperative complications of cataract surgery?

A

Posterior lens capsule rupture

Floppy iris syndrome

34
Q

What is floppy iris syndrome?

A

A flaccid iris that can complicated surgery in patients on alpha blockers e.g. tamsulosin

35
Q

How is floppy iris syndrome avoided in high risk patients?

A

Intracameral phenylephrine used to dilate pupils

36
Q

List some post-operative complications of cataract surgery

A

Early: corneal oedema, elevated IOP, acute endophthalmitis

Late: PCO (most common), Irvine-Gass syndrome (CMO post cataract surgery), retinal detachment, delayed endophthalmitis

37
Q

What is endophthalmitis?

A

Inflammation of the vitreous and aqueous humour, usually caused by infection. Characterised by progressive vitritis.

38
Q

What is the main mode of endophthalmitis prevention?

A

Pre-operative povidone-iodine 5% antiseptic

39
Q

What are the features of endophthalmitis?

A

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

40
Q

What is the treatment of endophthalmitis?

A

Intravitreal antibiotics or pars plana vitrectomy (only beneficial in patients with light perception only vision)

41
Q

What is the difference between acute versus delayed endophthalmitis?

A

Acute occurs in the first week and is due to ocular flora like staph. epidermidis

Delayed occurs from 6w to a few months and is mainly caused by propionibacterium acnes

42
Q

What are some other causes of endophthalmitis?

A

Post-trauma - staphylococcus and bacillus cereus has worst prognosis

Candida occurs in immunocompromised patients. Most common cause of endogenous endophthalmitis

43
Q

What is posterior capsular opacification?

A

This is the most common complication of later cataract surgery. Opacification occurs due to posterior migration of epithelial cells

44
Q

What are the features of PCO?

A

Gradual loss of vision and glare.

Elschnig pearls: grape-like collections of swollen epithelial cells

Sommering rings: white annular proliferation of residual cells

45
Q

How is PCO treated?

A

Capsulotomy with Nd:YAG laser

46
Q

Describe uni- / bilateral congenital cataracts

A

Bilateral (66%) AD inheritance

Unilateral are usually sporadic

47
Q

List some secondary causes of congenital cataracts

A 
Galactosaemia 
Lowe syndrome 
Fabry syndrome 
Mannosidosis 
Down Syndrome 
TORCH infections
48
Q

How are the following congenital cataracts treated:

Small partially dense

Unilateral cases

Surgical intervention

Bilateral dense

Unilateral dense

A

Observation for <3mm partially dense cataracts

Unilateral cases: occlusion/mydisasis in good eye can prevent amblyopia and delay need for surgery

Surgery - pars plana vitrectomy and posterior capsule capsulohexis (+/- anterior vitrectomy)

Correction of refractive errors

Bilateral dense requires surgery within 8-10w

Unilateral dense requires surgery within 6w due to risk amblyopia

49
Q

What are the postoperative complications of congenital cataract surgery?

A

PCO (can lead to amblyopia)

Secondary glaucoma

Endophthalmitis

Retinal detachment

50
Q

What is lenticonus?

A

Anterior and posterior varieties

Anterior: bilateral thinning of the anterior capsule with lens protrusion into AC. Assoc. w Alport Synd.

Posterior: deformity of post. surface of the lens; usually unilateral and associated with congenital cataract and Lowe syndrome.

51
Q

What is ectopia lentis?

A

Dislocation/displacement of the lens from its anatomical position. Most commonly ue to trauma

52
Q

List some ocular causes of ectopia lentis

A

Simple (familial) ectopia lentis

Pseudoexfoliation syndrome

Hypermature cataracts

High myopia

53
Q

List some systemic causes of ectopia lentis

A

Marfan syndrome

Homocystinuria

Ophthalmology (7 decks)

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