Lens And Cataracts Flashcards by Anna Annett

The lens is a ____ crystalline structure located between the ____ and _____.

Biconvex
Iris
Vitreous

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What us e power of an adult lens?

15-20D

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What is the refraction index of the lens and why?

Has a high protein content

Index of 1.4

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Define near accommodation:

Eye brings near objects closer into focus by contracting the ciliary muscles.
Zonules relax making the lens more spherical and increasing its power.

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Define far accommodation:

Eye brings far objects into focus by relaxing the ciliary muscles and increasing zonular tension - lens becomes flatter.

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What is the capsule composed of?

Outer transparent basement membrane
Thinnest posteriorly and thicker at the equators
Type 4 collagen and glycosaminoglycan
Anterior capsule thickens with age while the posterior one maintains its thickness

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What is the histology of the epithelium?

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

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Define cataract:

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

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Give some examples of age related cataracts:

Nuclear sclerotic
Cortical
Subcapsular
polychromatic (Christmas tree)

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What is the histology of the lens fibres

They elongate and push older fibres deeper into the lens. The nucleus is the innermost part and is present at birth - the cortex is outer part and contain the youngest fibres.
junction of the fibres for the anterior suture (Y shaped) and posterior suture (inverted y shape)

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Give the different types of cataract maturity:

Immature - partially opaque
Mature - fully opaque
hyper mature: shrunken anterior capsule due to leakage of material outside lens
Morgagnian: a specific form of hyper-mature cataracts which causes the nucleus to sink as the cortex liquifies.

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This type of cataract is characterised by a yellowing of the crystalline lens due to deposition of urochrome pigment:

Nuclear sclerotic

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How does a nuclear cataract affect the refractive index?

Increases due to the lens hardening. Causes a myopic shift allowing some elderly patients to read without glasses

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What type of cataract occurs due to the opacification of the lens cortex, characterised by wedge shaped opacities?

Cortical

Glare is the predominant symptom

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What is the main symptoms of a subcapsular (anterior or posterior) cataract?

Glare
Difficulty seeing in bright light
Near vision problems

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Acquired cataracts can be anterior or posterior. Give causes of each:

Anterior - Blunt trauma (flower shaped cataract)
- Atopic dermatitis (shield-like cataract)
- Wilsons disease
- Gold
- Infrared radiation
- Post congestive closed angle glaucoma
Posterior
- Corticosteroids
- Diabetes
- Retinitis pigmentosa
- NF2
- Chloroquine

What causes Christmas tree like cataracts?

Myotonic dystrophy

What disease can lead t pearly nuclear sclerotic cataracts?

Rubella

What type of cataract might be seen in hypothyroidism?

Polychromatic cataract

Downs Syndrome can lead to what type of cataract?

Blue dot cataract

What are the management options for cataracts?

Replacement of the diseased lens with an intraocular lens (IOL) using either of the following techniques:
Phacoemulsification
Extracapsular cataract extraction (may be used for very hard cataracts)

How is intraocular lens power calculated?

Measuring the corneal curvature and eye length.
Power = A - 2.5L - 0.9K

(A is a constant supplied by a manufacturer)
(L is axal length of eye)
(K is the average corneal power reading in diopters)

What are the two main types of Intraocular lens?

Rigid and Flexible

Describe rigid IOLs

Made from polymethylmethacrylate
Require larger incision
Higher rates of posterior opacification that flexible IOLs

Describe flexible IOLs:

Used in modern cataract surgery most Has 3 types: - Acrylic hydrophobic - has higher refractive index and lower rates of PCO but can cause dysphotopsia - Acrylic hydrophilic - higher biocompatibility but calcification may recur -Silicone - rarely used in Phacoemulsification

Give some advantages of using phacoemulsification over ECCE:

``` Smaller incision no sutures required faster recovery Less astigmatism Reduces complications ```

List some intraoperative complications which can occur from cataract surgery:

Posterior lens capsule rupture | Floppy iris syndrome

List some post op complications from cataract surgery:

Early - corneal oedema, elevated IOP, acute endophthalmitis | Late: PCO Irvine-Gass syndrome, retinal detachment, and delayed endophthalmitis

Define endophthalmitis:

This is inflammation of the vitreous and aqueous humour which is usually caused y an infection and is characterised by progressive vitritis. Main causative organism is staph aureus

How might you prevent endophthalmitis?

Using povidone-iodine 5% antiseptic to clean the eyes properly post op

How can endophthalmitis be managed?

Intravitreal antibiotics or pars plana vitrectomy

Give some features of posterior capsule opacification:

``` Gradual vision loss and increasing glare (patients feel cataracts have returned) Elschnig pearls (grape like collection of epithelial cells) Sommering rings (white annular proliferation of residual cells) ```

How is posterior capsule opacification managed?

Capsulotomy with an Nd:YAG laser

What are some secondary causes of congenital cataracts?

``` Galactosaemia Lowe syndrome Fabry disease Mannosidosis Downs TORCH intrauterine infections ```

How are congenital cataracts managed?

Observe for small <3mm ones In unilateral - past time occlusion of pharmacological mydriasis of god eye may help Surgery (Bilateral dense = surgery within 10 weeks of life) (Unilateral dense -surgery within 6 weeks of life)

Define lenticonus:

Anterior: this is when the anterior capsule thins bilaterally and has associated lens protrusion into the anterior chamber Posterior: Derformity of the posterior surface of the lens that is unalter.

What is anterior lenticonus often associated with?

Alport syndrome | Type IV collaged mutation disorder

What is posterior lenticonus often associated with

Lowe syndrome | Congenital cataracts

Define ectopia lentis:

This refers to the dislocation of the lens from its normal place and the most common cause is trauma. Can also be assoc. w/ ocular or systemic disease. Ocular - high myopia, hyper mature cataract, simple ectopia lentis, pseudoexfoliation syndrome Systemic: Marfans, homocystinuria