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Keratoconus

ROUTINE — Cornea

Symptoms

progressive decrease in vision (irregular astigmatism)

starbursts, ghosting, and halos around lights

onset typically during puberty; stabilizes in middle age

acute hydrops: sudden vision drop, pain, and profuse tearing

Clinical Findings

Classic slit-lamp tetrad

  • fleischer ring: brown-yellow epithelial iron deposit at the base of the cone
  • vogt striae: fine vertical deep-stromal stress lines (disappear with globe compression)
  • munson sign: v-shaped lower-lid indentation on downgaze due to cone protrusion
  • apical thinning: central or paracentral stromal thinning ± scarring

Early & optical signs

  • charleux "oil-droplet" red reflex on direct ophthalmoscopy
  • scissoring reflex on retinoscopy

Topography & tomography

  • topography: asymmetric inferior or inferotemporal steepening (i-s ratio > 1.4)
  • tomography (pentacam): posterior corneal elevation and thinning are earlier indicators than topography

Acute hydrops

  • dense central/inferior stromal edema from a rupture in descemet membrane
  • allows aqueous humor to flood the stroma; usually resolves over 2–4 months

Etiology

Pathogenesis

  • non-inflammatory progressive ectasia causing corneal thinning and protrusion
  • associated with chronic eye rubbing (strongest modifiable risk factor)
  • multifactorial: atopy, down syndrome, marfan syndrome, and ehlers-danlos
  • enzymatic imbalance leads to weakened stromal cross-linking

Red Flags

sudden pain and opacity (acute hydrops)

documented rapid topographic progression in a teenager/young adult

history of aggressive eye rubbing (requires immediate behavioral counseling)

severe thinning approaching the limbus (suspect pellucid marginal degeneration)

Investigations

Diagnostics

  • scheimpflug tomography (e.g., pentacam): mandatory for staging and CXL planning
  • computer-assisted topography: to map anterior curvature
  • pachymetry: to measure the thinnest point of the cornea
  • slit-lamp exam under cobalt blue light to highlight fleischer rings

Treatment

Non-surgical

  • behavioral: strict avoidance of eye rubbing
  • optical: glasses (mild), RGP lenses, or scleral lenses (moderate-to-severe)

Surgical & procedural

  • corneal cross-linking (CXL): uses riboflavin and UV-A to stabilize the stroma
  • intracorneal ring segments (icrs): to flatten the cone and improve lens tolerance
  • keratoplasty (dalk or pkp): for advanced scarring or contact lens intolerance

Hydrops management

  • conservative: cycloplegics, hypertonic saline (muro 128), and aqueous suppressants

Clinical Pearl

Keratoconus is a bilateral (though often asymmetric) progressive corneal ectasia. Onset typically puberty to 30s. Associated with eye rubbing, atopy, Down syndrome. Hydrops (acute stromal edema from Descemet rupture) presents with sudden vision loss and opacity — paradoxically reduces progression. CXL is the only treatment proven to halt progression.

Differential Diagnosis

  • pellucid marginal degeneration (inferior peripheral "crab-claw" thinning)
  • keratoglobus (global thinning from limbus to limbus)
  • post-refractive surgery ectasia
  • irregular astigmatism from corneal scarring

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