Keratoconus
The cornea thins and bulges into a cone in young people, blurring vision. Cross-linking can stop it; rigid lenses or a transplant restore vision.
What it is
A progressive, usually bilateral but asymmetric thinning of the central cornea, which bulges forward into a cone. It causes increasing irregular astigmatism and myopia, usually starting in adolescence and progressing until the thirties. Early treatment with corneal cross-linking can stop it.
Who gets it
Begins in adolescence or early adulthood. It is more common in people with atopy, Down syndrome and some connective tissue disorders.
Causes
- Genetic predisposition
- Chronic eye rubbing
- Atopy (allergic conjunctivitis, eczema, asthma)
- Down syndrome and connective tissue disorders
Risk factors
- Vigorous, habitual eye rubbing
- Allergic eye disease
- Family history
- Down syndrome
Pathophysiology
The collagen of the corneal stroma weakens and loses its regular arrangement. Under normal eye pressure the thin cornea bulges, its curvature becomes irregular and the image is distorted. In advanced cases a break in Descemet membrane lets aqueous into the stroma (acute hydrops).
Symptoms and signs
- Progressive blurred and distorted vision
- Frequent changes of glasses prescription
- Glare, halos and ghost images
- Light sensitivity
Diagnosis
- Clinical
- Suspected from progressive irregular astigmatism and poor correction with glasses; at the slit lamp, central thinning and a cone may be seen in advanced cases.
- Tests
- Corneal topography and tomography (thickness maps) confirm it and show progression.
- Imaging
- Corneal tomography is the key study; no other imaging is needed.
Differential diagnosis
- Regular astigmatism
- Ectasia after laser refractive surgery
- Pellucid marginal degeneration
- Corneal scarring
Goal of treatment
Stop progression early and restore useful vision.
Treatment
- Lifestyle
- Stop eye rubbing and treat allergic eye disease.
- Procedure
- Corneal collagen cross-linking with riboflavin and ultraviolet light to halt progression.
- Conservative
- Glasses in early stages, then rigid gas-permeable or scleral contact lenses.
- Surgical
- Corneal transplant (keratoplasty) in advanced disease or after scarring.
Complications
- Severe visual loss from irregular astigmatism
- Acute hydrops and corneal scarring
- Contact lens intolerance
Prognosis
Progression usually stops by the thirties or forties. With early cross-linking most patients keep useful vision; transplant results are good.
Prevention
- Avoid eye rubbing
- Screen with topography before laser refractive surgery
Test yourself
Think of the answer, then tap the question to see it.
What is keratoconus?
A progressive thinning and cone-shaped bulging of the cornea that causes irregular astigmatism.
Which treatment stops its progression?
Corneal collagen cross-linking.
Which habit is a modifiable risk factor?
Habitual, vigorous eye rubbing.
Why it happens
In ophthalmology
- Corneal transplant (keratoplasty) and the artificial cornea
- Corneal topography, tomography and specular microscopy
Connections
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Keratoconus (StatPearls Publishing (NCBI Bookshelf), 2024); Collagen Cross Linking for Keratoconus (StatPearls Publishing (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.