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