Keratoconus (conical cornea) is a disease in which thinning, ectasia (bulging), and scarring of the cornea occurs. It usually affects both eyes, but not always equally. The ectasia progresses over a variable period of years. This process often results in irregular astigmatism and blurred vision which cannot be corrected with spectacles. Eye rubbing may accelerate the progression of keratoconus.
Keratoconus may be difficult to diagnose in its initial stages. The onset is often around puberty. The most common early symptoms are progressive myopia (nearsightedness) and astigmatism.
Slit lamp examination in the office may reveal corneal stress lines (Vogt’s striae), iron deposition in the surface epithelial layers at the base of the cone (Fleischer ring), characteristic thinning, and corneal scars. A keratometer will demonstrate the higher curvature seen in keratoconus. Corneal topography provides a more detailed measurement of the corneal curvature and is one of the best ways of confirming the diagnosis.
The heredity of keratoconus is not fully established. Different inheritance patterns – dominant, recessive, or none – have been described. The overall chance of a blood relative developing keratoconus, especially significantly symptomatic keratoconus, is fairly low.
Keratoconus may be associated with other conditions. These include:
- Atopic disease (atopic dermatitis, asthma)
- Down’s syndrome
- Marfan’s syndrome
- Ehlers-Danlos syndrome
- Vernal keratoconjunctivitis
- Eye rubbing
- Mitral valve prolapse
In advanced cases of keratoconus, the innermost layer of the cornea (Descemet’s membrane) can rupture, resulting in rapid corneal swelling (corneal hydrops). Symptoms of blurred vision, light sensitivity, and pain can occur. Eye drops are used to control some of the symptoms. The swelling, with resultant blurred vision, almost always resolves over time, but may last up to 3 months. The visual acuity end-result may be worse, better, or the same as before the hydrops occurred.
Treatment of keratoconus must be individualized for each patient. In early stages, vision may be corrected with spectacles. Patients should be counseled to avoid eye rubbing and to control causes of ocular itching which may lead to excessive eye rubbing.
When clear, comfortable vision with spectacles is not possible, a rigid gas permeable (RGP) contact lens is recommended. The RGP lens masks the irregular corneal surface by becoming the new refractive surface of the eye, with the tear film filling in the irregularities between the back of the contact lens and the front of the cornea. Fitting these lenses may be difficult and time-consuming, requiring an experienced contact lens fitter.
INTACS are arc-shaped segments that can be implanted surgically to improve the ability to wear contact lenses comfortably. Some improvement in uncorrected vision may also be achieved. INTACS may delay corneal transplant surgery. One of the advantages of INTACS is their reversibility.
Collagen Cross Linking (CXL) is an advanced treatment to stabilize the cornea in patients with keratoconus and prevent progression of vision loss. Any patient diagnosed with keratoconus, especially if younger than 40 years old or with worsening disease, should be seen quickly and considered for CXL before their cornea becomes too thin to safely perform CXL.
A corneal transplant (penetrating keratoplasty or deep anterior lamellar keratoplasty) may be considered to restore vision when keratoconus progresses to the point where a contact lens cannot be fitted successfully, or corneal scarring is severe enough to preclude good vision with a contact lens. Corneal transplant surgery has a very good prognosis in the treatment of keratoconus. Potential risks and complications exist. Corneal transplants are generally recommended if contact lenses are unsatisfactory.