Lens And Cataracts

Question 1

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

Answer 1

Biconvex
Iris
Vitreous

Question 2

What us e power of an adult lens?

Answer 2

15-20D

Question 3

What is the refraction index of the lens and why?

Answer 3

Has a high protein content

Index of 1.4

Question 4

Define near accommodation:

Answer 4

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

Question 5

Define far accommodation:

Answer 5

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

Question 6

What is the capsule composed of?

Answer 6

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

Question 7

What is the histology of the epithelium?

Answer 7

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

Question 8

Define cataract:

Answer 8

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

Question 9

Give some examples of age related cataracts:

Answer 9

Nuclear sclerotic
Cortical
Subcapsular
polychromatic (Christmas tree)

Question 10

What is the histology of the lens fibres

Answer 10

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)

Question 11

Give the different types of cataract maturity:

Answer 11

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.

Question 12

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

Answer 12

Nuclear sclerotic

Question 13

How does a nuclear cataract affect the refractive index?

Answer 13

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

Question 14

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

Answer 14

Cortical

Glare is the predominant symptom

Question 15

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

Answer 15

Glare
Difficulty seeing in bright light
Near vision problems

Question 16

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

Answer 16

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

Question 17

What causes Christmas tree like cataracts?

Answer 17

Myotonic dystrophy

Question 18

What disease can lead t pearly nuclear sclerotic cataracts?

Answer 18

Rubella

Question 19

What type of cataract might be seen in hypothyroidism?

Answer 19

Polychromatic cataract

Question 20

Downs Syndrome can lead to what type of cataract?

Answer 20

Blue dot cataract

Question 21

What are the management options for cataracts?

Answer 21

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)

Question 22

How is intraocular lens power calculated?

Answer 22

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)

Question 23

What are the two main types of Intraocular lens?

Answer 23

Rigid and Flexible

Question 24

Describe rigid IOLs

Answer 24

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

Question 25

Describe flexible IOLs:

Answer 25

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

Question 26

Give some advantages of using phacoemulsification over ECCE:

Answer 26

Smaller incision
no sutures required
faster recovery
Less astigmatism
Reduces complications

Question 27

List some intraoperative complications which can occur from cataract surgery:

Answer 27

Posterior lens capsule rupture

Floppy iris syndrome

Question 28

List some post op complications from cataract surgery:

Answer 28

Early - corneal oedema, elevated IOP, acute endophthalmitis

Late: PCO Irvine-Gass syndrome, retinal detachment, and delayed endophthalmitis

Question 29

Define endophthalmitis:

Answer 29

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

Question 30

How might you prevent endophthalmitis?

Answer 30

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

Question 31

How can endophthalmitis be managed?

Answer 31

Intravitreal antibiotics or pars plana vitrectomy

Question 32

Give some features of posterior capsule opacification:

Answer 32

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)

Question 33

How is posterior capsule opacification managed?

Answer 33

Capsulotomy with an Nd:YAG laser

Question 34

What are some secondary causes of congenital cataracts?

Answer 34

Galactosaemia
Lowe syndrome
Fabry disease
Mannosidosis
Downs 
TORCH intrauterine infections

Question 35

How are congenital cataracts managed?

Answer 35

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)

Question 36

Define lenticonus:

Answer 36

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.

Question 37

What is anterior lenticonus often associated with?

Answer 37

Alport syndrome

Type IV collaged mutation disorder

Question 38

What is posterior lenticonus often associated with

Answer 38

Lowe syndrome

Congenital cataracts

Question 39

Define ectopia lentis:

Answer 39

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