Unit 4: Refractive Error
3: Refractive Errors
Keratoconus
Keratoconus is a bilateral (85% of cases) acquired, corneal collagen disorder , in which the cornea, thins and distorts. Peak onset is usually in late teens to twenties.
Systemic associations include:
- Downs syndrome
- Ehlers-Danlos syndrome
- Marfans syndrome
Signs
- Increase in corneal astigmatism and often myopia
- Abnormal retinoscopy reflex (appears like a oil droplet)
- Retinoscope reflex shows scissors movement
- Central corneal thinning and conical shape (steepening of corneal curvature)
- Bulging of the lower lid on down gaze
- Vertical lines in the corneal stroma (striae)
Management
- Contact lenses, fit with Rigid gas permeable for optimum visual acuity, often better than spectacles.
- Often photorefractive surgery is contraindicated
- Can require corneal graft in late stages if scarring present
- Monitor regularly for progression.
