Keratoconus
A progressive eye disease where the clear front surface of the eye (cornea) thins and bulges into a cone shape, distorting vision.
Emergency Management: Acute corneal hydrops requires urgent ophthalmology evaluation. Managed conservatively with hypertonic saline (5% drops), cycloplegics, and occasionally injection of intracameral gas (SF6) to tamponade the rupture.
Keratoconus is a progressive, non-inflammatory, bilateral (though often asymmetric) ectatic corneal disease characterized by localized corneal thinning and steepening. This results in the cornea assuming a conical shape, causing irregular astigmatism and significant visual impairment.
Detailed Overview
The disease typically manifests at puberty and progresses until the third or fourth decade of life before stabilizing. The biomechanical weakening of the corneal stroma causes the cornea to bulge forward. Initial symptoms include blurred vision and frequent changes in spectacle prescription due to progressive myopia and irregular astigmatism. As the disease advances, glasses fail to correct the vision, necessitating rigid gas-permeable contact lenses. In advanced cases, Descemet's membrane can rupture causing acute corneal hydrops, or severe scarring can occur, eventually requiring corneal transplantation.
Epidemiology & Demographics
Estimated prevalence is roughly 1 in 2,000 in the general population, but much higher in certain ethnicities (e.g., Middle Eastern, South Asian). Onset is typically in the teens to early twenties.
Etiological Mechanism
Multifactorial; a combination of genetic predisposition (e.g., family history, Down syndrome) and environmental mechanical factors, most notably vigorous eye rubbing.
Primary Causes
["Genetic predisposition (associated with Down syndrome, Marfan syndrome, Ehlers-Danlos)", "Chronic mechanical trauma (vigorous eye rubbing)", "Atopic diseases (allergic conjunctivitis, eczema) which predispose to eye rubbing"]
At the cellular level, keratoconus involves increased degradative enzyme activity (matrix metalloproteinases) and decreased inhibitors, leading to the breakdown of collagen cross-links in the corneal stroma. The loss of stromal mass and structural integrity allows the normal intraocular pressure to push the thinned cornea outward, creating a paracentral conical protrusion. This induces high irregular astigmatism and higher-order aberrations, degrading retinal image quality.
Diagnostic Criteria & Guidelines
Diagnosis is established via corneal topography/tomography showing localized areas of abnormal corneal steepening (high keratometry values >47 Diopters) and pachymetry showing focal corneal thinning in the matching areas.
Visual rehabilitation: Spectacles for very early disease, transitioning to Rigid Gas Permeable (RGP) contact lenses or Scleral lenses to mask the irregular astigmatism. Disease stabilization: Corneal Collagen Cross-Linking (CXL) using topical Riboflavin drops and UV-A light to halt progression.
Second-Line & Adjunctive Therapy
Intrastromal corneal ring segments (ICRS, e.g., Intacs) implanted via femtosecond laser to flatten the cornea and improve contact lens tolerance in moderate cases.
Surgical & Procedural Management
Deep Anterior Lamellar Keratoplasty (DALK) or Penetrating Keratoplasty (PK) (full-thickness corneal transplant) for advanced disease with severe scarring or intolerance to contact lenses.
Patient Counseling & Advice
Inform the patient that CXL stops the disease from getting worse but does not reverse it; contact lenses will still be needed. Emphasize the absolute necessity of not rubbing the eyes.
Follow-Up & Monitoring Schedule
Serial corneal topography every 6-12 months to monitor for disease progression, especially in younger patients (<30 years) where the disease is most active.
Preventive Strategies
Early detection via screening topography in patients with changing astigmatism and strict avoidance of eye rubbing. Early CXL prevents progression.
Excellent with modern interventions. CXL successfully halts progression in >90% of cases. Visual outcomes with scleral lenses are outstanding. About 10-20% historically progressed to needing transplants, but this is decreasing due to widespread CXL use.