Keratoconus
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Direct answer
Spectacle prescriptions that change every few months in a late teenager, with astigmatism the optician cannot fully correct, is how keratoconus usually announces itself — a bilateral, typically asymmetric, non-inflammatory thinning and conical protrusion of the cornea. Diagnosis is topographic before it is clinical: inferior corneal steepening on computerised videokeratography with thinning at the cone apex. Early disease manages with glasses, then rigid gas-permeable contact lenses once astigmatism escapes spectacles; progressive thinning is halted by collagen cross-linking (riboflavin plus ultraviolet-A, the C3R procedure), and the end-stage scarred cornea needs deep anterior lamellar or penetrating keratoplasty. Acute hydrops — a break in Descemet membrane with sudden corneal oedema — is managed expectantly, since the cornea usually clears in months.
What you must remember
- Eponymous signs: Munson sign (bulging of the lower lid on downgaze), Rizutti sign (a conical reflection at the nasal limbus when light is shone from the temporal side), Vogt striae (vertical stromal stress lines that disappear on pressure), Fleischer ring (iron deposition at the cone base), and the oil-drop red reflex plus scissoring on retinoscopy.
- Diagnosis: corneal topography showing inferior steepening is the standard; pachymetry documents apical thinning; the Amsler-Krumeich classification grades by refraction, keratometry values, corneal thickness and corneal haze.
- Associations: eye rubbing (atopy, vernal keratoconjunctivitis — common in India), Down syndrome, Leber congenital amaurosis, connective tissue disorders, and a family history suggesting genetic contribution.
- Acute hydrops: sudden pain, photophobia and hazy vision from a Descemet tear; treatment is supportive with cycloplegia, hypertonic saline and, when healing leaves a cleavage, later options — resolution takes weeks to months and often leaves a scar.
- Collagen cross-linking (C3R): riboflavin 0.1 per cent photosensitiser activated by ultraviolet-A (commonly 3 mW/cm² for 30 minutes) creates covalent bonds that stiffen the stroma and arrest progression — the only proven disease-modifying treatment.
- Surgical ladder: intrastromal ring segments (INTACS) flatten the cone in contact-lens-intolerant moderate disease; deep anterior lamellar keratoplasty suits stromal disease with healthy endothelium; penetrating keratoplasty is reserved for scars involving full thickness.
- Absolute red flag: keratoconus or abnormal topography contraindicates LASIK, which can precipitate catastrophic corneal ectasia.
From suspicion to cross-linking, step by step
An 18-year-old student reports that his right spectacle pair, made eight months ago, already blurs. Refraction shows myopic astigmatism of 3 dioptres that will not neutralise; retinoscopy scissors across the pupil; the corrected vision stalls at 6/12. Order corneal topography rather than a stronger prescription. The map shows inferior steepening with a difference of several dioptres between superior and inferior cornea, and pachymetry reads thin at the apex. He admits to rubbing his eyes hard every summer since childhood. Staging is mild to moderate; counsel him first about rubbing cessation, since mechanical trauma drives progression. Correct with glasses now; when vision fails again, fit a rigid gas-permeable lens that vaults the cone with a tear lens providing the optics. Because his topography over the next six months shows steepening of more than a dioptre, he qualifies for cross-linking: remove the epithelium, saturate the stroma with riboflavin, irradiate with ultraviolet-A, apply a bandage contact lens, and review the next day. The procedure does not remove the need for glasses; it freezes the disease. Were he instead to arrive with a painful white cornea and marked oedema after years of an unmanaged cone, that is hydrops — wait it out, then reassess refraction; only a dense central scar years later sends him to the keratoplasty list.
Where the exam frames it
Three question templates dominate. First, eponym matching — a clinical photograph or vignette is tagged Munson, Rizutti, Vogt or Fleischer, and candidates must pair sign with disease rather than merely reciting the list. Second, the management ladder is tested as a sequence: spectacles, rigid lenses, cross-linking, ring segments, keratoplasty — and the trap option is always LASIK, which sounds modern but is contraindicated. Third, hydrops appears as an acute painful eye in a known keratoconic, asking for supportive care rather than surgery; examiners reward cycloplegia and observation because operating on an oedematous cornea invites disaster. A viva favourite in Indian settings is the vernal catarrh link: the child who rubs itchy eyes for a decade is the cohort that presents with cones in the second decade, so treating allergy is keratoconus prevention in disguise.
Frequently asked questions
What is the most useful investigation for diagnosing keratoconus?
Corneal topography, which shows inferior or paracentral steepening long before slit-lamp signs appear, complemented by pachymetry demonstrating apical thinning.
What happens in acute corneal hydrops?
A break in Descemet membrane allows aqueous to flood the stroma, causing sudden pain, photophobia and oedema; treatment is supportive and the cornea usually clears over weeks to months, often with scarring.
How does collagen cross-linking work?
Riboflavin soaked into the stroma is activated by ultraviolet-A light, generating covalent cross-links between collagen fibrils that stiffen the cornea and halt progression.
Why is LASIK contraindicated in keratoconus?
Thinning and weakening ectatic cornea plus stromal laser ablation precipitates progressive iatrogenic ectasia and loss of vision.
Which corneal graft option suits advanced keratoconus?
Deep anterior lamellar keratoplasty is preferred when the endothelium is healthy, avoiding endothelial rejection; penetrating keratoplasty is reserved for full-thickness scars.