Keratoconus / Conical cornea

Keratoconus (Conical cornea)
Manifestations:
  • Progressive corneal steepening, most typically inferior to the center of the cornea
  • Non-inflammatory bilateral ecstatic condition of cornea with Protrusion of anterior cornea and characterized paraxia/stromal thinning
  • Usually starts at puberty and progresses slowly
  • Progressive myopia, regular and irregular astigmatism — does not improve fully despite full correction with glasses
  • Eye rubbing is strongly associated with the development of keratoconus.
  • The cytokine interleukin-1 has been suggested as a mediator of eye rubbing and stromal degradation
Signs
  • Munson's sign – bulging of lower lid on downward gaze
  • Rizutti sign - focusing of a light beam shone from temporally across the cornea in an arrowhead pattern at the nasal limbus
  • Window reflex is distorted
  • Placido disc – irregular circles
  • Keratometry – extreme malalignment of mires
  • Photokeratoscopy – distortion of circle
  • Enlarged corneal nerves
Slit lamp examination
Hall mark -

  • Thinning and ectasia of central corner 
  • Fleischer's ring at the base of cone due to iron deposition
  • Folds in Descemet's and Bowman's membrane
  • Vogt lines–deep stromal striae (which disappear with external pressure)
Retinoscopy:
  • yawning reflex (scissor reflex)
 Distant direct ophthalmoscopy:
  • oil droplet reflex of Charleaux (a dark reflex in the area of the cone on observation of the cornea with the pupil dilated)
Complications:
  • Acute corneal hydrops due to rupture of Descemet's membrane (especially in Down syndrome)
Management of early cases:
  • spectacles, rigid gas permeable contact lenses, intacs (intracorneal ring segments)
  • Corneal collagen cross linking with riboflavin – slows the progression of disease
  • Late stages – Deep anterior lamellar keratoplasty or Penetrating keratoplasty
Exam Question
  • Non-inflammatory bilateral ecstatic condition of cornea with Protrusion of anterior cornea and characterized paraxia/stromal thinning
  • Progressive myopia, regular and irregular astigmatism
  • Munson's sign – bulging of lower lid on downward gaze 
  • Placido disc – irregular circles
  • Fleischer's ring at the base of cone due to iron deposition
  • Acute corneal hydrops due to rupture of Descemet's membrane (especially in Down syndrome)
  • Spectacles, rigid gas permeable contact lenses, intacs (intracorneal ring segments)
  • Late stages – Deep anterior lamellar keratoplasty or Penetrating keratoplasty
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