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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
What are the associations with development of posterior subcapsular cataracts?
``` Corticosteroids Diabetes (snowflake shaped) Retinitis pigmentosa NF2 Chloroquine ```
26
List some other types of cataract
Christmas tree-like cataract (myotonic dystrophy) Pearly nuclear sclerotic cataract (Rubella) Blue dot cataract (Down syndrome) Polychromatic cataract (hypoparathyroidism)
27
What are the two surgical treatment methods from cataract?
Phacoemulsification (gold standard) Extracapsular cataract extraction (may be used for very hard cataracts)
28
What are the advantages of phacoemulsification over ECCE?
Smaller incision Less astigmatism Faster recovery Reduced complications No sutures needed (most of the time)
29
How is intra-ocular lens power calculated?
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
What are the two different types of IOL used in cataract surgery?
Rigid or flexible IOLs
31
Outline what rigid IOLs are
Made of polymethylmethacrylate (PMMA) and requires larger incision and has higher rates of posterior capsule opacification than flexible counterparts
32
What are the three types of flexible IOL?
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
List some intraoperative complications of cataract surgery?
Posterior lens capsule rupture Floppy iris syndrome
34
What is floppy iris syndrome?
A flaccid iris that can complicated surgery in patients on alpha blockers e.g. tamsulosin
35
How is floppy iris syndrome avoided in high risk patients?
Intracameral phenylephrine used to dilate pupils
36
List some post-operative complications of cataract surgery
Early: corneal oedema, elevated IOP, acute endophthalmitis Late: PCO (most common), Irvine-Gass syndrome (CMO post cataract surgery), retinal detachment, delayed endophthalmitis
37
What is endophthalmitis?
Inflammation of the vitreous and aqueous humour, usually caused by infection. Characterised by progressive vitritis.
38
What is the main mode of endophthalmitis prevention?
Pre-operative povidone-iodine 5% antiseptic
39
What are the features of endophthalmitis?
Progressive vitritis (blurred vision and floaters), pain, hypopyon and corneal haze
40
What is the treatment of endophthalmitis?
Intravitreal antibiotics or pars plana vitrectomy (only beneficial in patients with light perception only vision)
41
What is the difference between acute versus delayed endophthalmitis?
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
What are some other causes of endophthalmitis?
Post-trauma - staphylococcus and bacillus cereus has worst prognosis Candida occurs in immunocompromised patients. Most common cause of endogenous endophthalmitis
43
What is posterior capsular opacification?
This is the most common complication of later cataract surgery. Opacification occurs due to posterior migration of epithelial cells
44
What are the features of PCO?
Gradual loss of vision and glare. Elschnig pearls: grape-like collections of swollen epithelial cells Sommering rings: white annular proliferation of residual cells
45
How is PCO treated?
Capsulotomy with Nd:YAG laser
46
Describe uni- / bilateral congenital cataracts
Bilateral (66%) AD inheritance Unilateral are usually sporadic
47
List some secondary causes of congenital cataracts
``` Galactosaemia Lowe syndrome Fabry syndrome Mannosidosis Down Syndrome TORCH infections ```
48
How are the following congenital cataracts treated: Small partially dense Unilateral cases Surgical intervention Bilateral dense Unilateral dense
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
What are the postoperative complications of congenital cataract surgery?
PCO (can lead to amblyopia) Secondary glaucoma Endophthalmitis Retinal detachment
50
What is lenticonus?
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
What is ectopia lentis?
Dislocation/displacement of the lens from its anatomical position. Most commonly ue to trauma
52
List some ocular causes of ectopia lentis
Simple (familial) ectopia lentis Pseudoexfoliation syndrome Hypermature cataracts High myopia
53
List some systemic causes of ectopia lentis
Marfan syndrome | Homocystinuria

Ophthalmology (7 decks)

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