11.4.2 Lens

Question 1

What parts are responsible for refractive surfaces?

Answer 1

• Cornea (avascular)
• Lens
  responsible for focusing clear image on retina

Question 2

Cataract
Define
Categories
Epidemiology
Etiology

Answer 2

Def - any opacity or discolouration of the lens - varies from a localised opacity ↔ total loss of clarity. (Lens is not transparent)

• It is also known as lens sclerosis - described according to the part(s) of the lens which are involved:
  • Subcapsular - in the cortex immediately under the capsule
  • Cortical - in the deeper cortex
  • Nuclear – in the nucleus Cataracts are common in the elderly.

Epidemiology
- 65-75 years - 70% have some degree of lens sclerosis & 20% have visual disability
- 75-85 years - 90% have some degree of lens sclerosis & 40% have visual disability

Aetiology
- Age
- Infective causes (especially babies)
- Genetics
- Trauma (unilateral)
- Uveitis
- Drug (steroids)
- Metabolic causes (DM)
- Smoking

Question 3

Cataract symptoms

Answer 3

• gradual painless loss of vision (NB)
• Monocular diplopia may occur if the lens develops areas/foci of differing refractive power (double vision)
• Vision may vary with illumination - may improve in either bright or dim light
• A nuclear cataract often increases the refractive power of the lens and myopia results - the patient is once again able to read without reading glasses

Myopic- short sighted

Question 4

Cataract diagnosis

Answer 4

• ⬇️ VA in a comfortable white eye
• Inspection - leukocoria (if advanced)
• Ophthalmoscopy:
  • An opacity in the red reflex that is localised at or just behind the level of the pupil
  • If advanced the red reflex may be absent
  • Dull or absent image of the fundus

Question 5

Cataract complications

Answer 5

Phacolytic glaucoma
- In cataract which is so far advanced that lens is completely white = lens proteins leak through the lens capsule into the anterior chamber → macrophages swollen with phagocytosed lens material block the trabecular meshwork & obstruct aqueous outflow = 2°glaucoma.

Phacoanapylactic uveitis
- Rupture of the lens capsule releases large amounts of lens proteins into the anterior chamber.
- May occur spontaneously in an advanced cataract, or as the result of trauma.
- The lens proteins excite an inflammatory reaction → severe anterior uveitis

Question 6

Congenital cataract

Answer 6

• Every newborn must undergo a general physical examination just after birth, and this must include examination of the red reflex - if a normal red reflex is not present, a thorough eye examination with dilated pupils must be performed.
• If a cataract is present - surgery is (ideally) performed before the age of 3 months to prevent the development of amblyopia.
• Visual results are unfortunately often disappointing
• INFECTION (rubella, herpes, syphilis)

Question 7

Ectopia lentis
Types
Causes
Complications

Answer 7

Types
- Subluxation = the lens only partially displaced due to rupture of some of the zonules.
- Dislocation = the lens completely displaced into either the anterior chamber or the vitreous humour.

Causes
- Trauma
- Collagen/connective tissue disease(s) with weak zonules - Marfan’s syndrome/disease

Complications
- displaced lens may cause pupil block & acute angle-closure glaucoma