Ectasias

Keratoconus

• Most common corneal ectasia

• Progressive conical distortion of the cornea

  • Corneal steepening centrally
  • Vogt striae: disappear on pressure
  • Fleischer ring (iron deposition at the base of the cone)
  • Munson’s sign: conical distortion of the lid on downgaze
  • Rizzuti sign: sharply focussed conical reflection on the nasal cornea from a temporal light source due to total internal reflection
  • Charleaux’s sign: dark reflex at the cone on observing the cornea against a dilated pupil with direct ophthalmoscopy
  • Scissoring reflex on retinoscopy
  • Oil droplet reflex

• Irregular astigmatism: bilateral but asymmetric

• Axial stromal thinning

• Axial protrusion

• Increasing myopia

• Usually stabilises by mid-30s

Aetiology

• Eye rubbing (and contact lens wear also a risk factor)
• Stromal abnormality/connective tissue disorder
• Familial possibly autosomal dominant element but most are sporadic
• Fragmentation of Bowman’s layer leading to forward bowing of the cornea
• There is evidence of familial inheritance in 15% of cases (?abnormal superoxide dismutase)

Associations

• Primary/idiopathic

• Allergic

  • Vernal keratoconjunctivitis
  • Eczema/asthma/hayfever/atopy
  • Floppy eyelid syndrome

• Congenital disorders:

  • Retinitis pigmentosa
  • ROP
  • Aniridia
  • Lebers congenital amaurosis

• Connective tissue disease

  • Ehlers-danlos syndrome
  • Marfan’s syndrome
  • Osteogenesis imperfecta/blue sclera

• Down syndrome: higher incidence of hydrops

• Apert’s syndrome (craniosynostosis)

Complications

• Acute hydrops: Descemet's rupture leading to acute oedema and scarring

Tomography

• Inferior steepening or asymmetrical bow-tie appearance
• High central power (esp. Compared to fellow eye)
• Large difference between centre and periphery
• Steepness disparity between the eyes
• Inferotemporally displaced steep cone
• Mild: <48D; moderate: 48-54D; severe: >54D
• Thinnest portion is at the apex of the cone

Management

• Counselling

• Spectacle or CL correction

  • Rigid gas permeable lens for moderate astigmatism
  • Intracorneal ring segment insertion: support the ectatic area to reduce steepening but do not affect progression

• Collagen crosslinking: riboflavin photosensitises the eye and then UV-A light is applied at a wavelength of 365nm. The interaction between these two leads to crosslinking within the collagen and ECM of the stroma (and avoids affecting the endothelium).

  • Limited use to corneas with >400microns in thickness to avoid endothelial toxicity
  • Has also been shown to reverse astigmatism

• DALK: is Descemet’s intact, ie. never had hydrops

• PK

• Supportive management (steroid, lubricants, hypertonic saline) of hydrops: injection of SF6 or C3F6 gas into the AC has been shown to promote closure of the rupture in Descemet’s.

• LASIK is contraindicated (can lead to corneal ectasia)

• Compare to contact lens warpage: long-term contact lens wear inducing irregular astigmatism with a cone but no other feature of keratoconus. Can be managed by discontinuing contact lens wear

Pellucid marginal degeneration

• Rare bilateral progressive ectasia

  • Inferior thinning of the cornea
  • Protrusion above the area of thinning (cp. keratoconus)

• Non-hereditary, non-inflammatory

• M = F

• Affects the peripheral cornea

• Presents in the 3rd to 5th decades

Clinical features

• Painless visual distortion
• Crescentic thinning (no vascularisation or lipid deposition)
• Especially affects the inferior cornea: cornea protrudes above the area of maximal inferior thinning
• Marked against-the-rule astigmatism
• Hydrops is rare
• Topography: crab-claw appearance

Management

• Rigid CLs
• Surgery can be tried but is often disappointing

Keratoglobus

• Globular overall appearance of the cornea

• Thinnest in the periphery

• Generalised protrusion of the cornea

• Typically present at birth

• Complications: corneal perforation/rupture

• Associations

  • Ehlers-danlos
  • Blue sclera
  • Flexible joints
  • Fractures
  • Deafness