Keratoconus

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Findings

  • progressive stromal thinning and protrusion
  • Irregular astigmatism; scissor reflex on retinoscopy
  • Vogt’s striae = very fine, vertical deep stromal striations, disappear with pressure applied over the eyeball
  • Oil drop sign in direct ophthalmoscopy
  • Fleischer ring = iron deposits around the base of the keratoconus
  • Central corneal opacity = tears in Bowman’s membrane and scarring (indicating progression of the keratoconus)
  • Salzmann’s nodule-like superficial scarring = Caused by rubbing from rigid contact lens
  • Munson’s sign = protrusion of the lower eyelid on downgaze
  • Hydrops = Descemet’s tear -> corneal oedema (usually closes on its own within 6 – 12 months)

Work-up

  • Clinical findings
  • Topography:
    • Shape: island-shaped elevation of the posterior surface > anterior surface = central ectasia
    • Corneal thickness/thinnest point
    • K-value: increase in refractive power (Kmax > 48dpt. not physiological)
    • D-value (Belin-Ambrosio coefficient): summarising overall parameter -> severity of keratoconus (the higher the value, the more pronounced the keratoconus)
  • Subclinical keratoconus
    • typically abnormal posterior elevation, abnormal pachymetry
    • Visual acuity normal, as anterior corneal surface typically not yet affected!

Management

  • Flowchart
  • Instruct patients to avoid eye rubbing!
  • Rigid contact lenses or mini scleral lenses -> possible up to Kmax of ∼70
  • Corneal Crosslinking (CXL) with riboflavin eye drops
    • Indication: Progression of keratoconus ectasia
    • Objective: Stabilisation/prevention of progression
  • Methods: epi-on = epithelium is not abraded beforehand or epi-off = with preceding epithelial abrasion
    • Contraindication: thinnest area of cornea = < 400µm
    • Risks: Scarring
    • Demarcation line between treated and untreated stroma
  • Keratoplasty: DALK or PKP (fitting of a mini-scleral lens after PKP after 4-6 months at the earliest).
  • (implantation of an intracorneal ring segment (Intacs))
  • in acute hydrops:
    • Consider NaCl Dispersa eye drops 5% 3-5 times daily (although usually not sufficient)
    • Consider cycloplegia (pain management)
    • Consider bandage contact lens
    • Consider bandage or glasses to protect against trauma/eye rubbing
    • usually spontaneous healing within 6-10 weeks
    • Consider corneal suture, air/gas injection
    • PKP not indicated in acute phase!

Follow-up

  • in young patients (between the ages of 12 and 18) and questionable progression of keratoconus: follow-up after 3 months, if stable 6-monthly
  • in older patients (> 20 years): follow-up every 6-12 months
  • Relevant progression of keratoconus is rare in patients above 35/40 years
  • Reliable progression parameters:
    • Form
    • K-value (Kmax not very reliable)
    • D (Belin-Ambrosio coefficient)
    • Corneal thickness
    • Astigmatism (not so meaningful, as average)

Possible concomitant diseases

  • Down’s, Turner’s, Ehlers-Danlos and Marfan syndromes, atopy, osteogenesis imperfecta, mitral valve prolapse
  • Pregnancy
  • Hyper-/hypothyroidism

Pellucid marginal degeneration

  • Important differential diagnosis!
    • might be a different phenotype of the same disease
  • painless peripheral corneal thinning inferiorly
    • crescent 1-2mm wide band inferiorly (typically from 4-8 o’clock), approx. 1mm distance from limbus
    • intact epithelium
  • no inflammation visible
  • corneal protrusion above the thinnest part
  • no Fleischer ring, no Vogt striae, hydrops very rare
  • Corneal topography: crab claw-like pattern with high astigmatism and “steepening” of inferior cornea
  • Therapy identical to keratoconus; PKP however more difficult due to peripheral thinning

Sources