Stages of Keratoconus
Keratoconus advances at varying rates and differently in each eye. Progression is generally more rapid, the earlier the age of onset. Keratoconus causes increasing blurriness and shortsightedness in vision, light sensitivity and halos and ghosting around light sources. Progression usually occurs to an age of around 40-45 years and then tends to stabilize. However some progression may be experienced by persons 50 or older. On average, the most significant progression occurs in the first 15-20 years after the time of onset.
Corneal collagen crosslinking, a procedure designed to harden the cornea and halt progression, is widely offered to patients today to prevent progression to the advanced and severe stages of keratoconus. It is hoped that in the future, crosslinking will significantly reduce rates of corneal transplantation and the difficulty of fitting contact lenses to keratoconus patients.
Early keratoconus
Forme Fruste keratoconus has only very slight corneal distortion; it has little or no effect on the quality of vision and exhibits minimal or no progression. Spectacles are usually successful in correcting the myopia and astigmatism and give adequate vision. Soft contact lenses, spherical or with a toric correction, can be a good option for general use or just for sporting activities.
Moderate keratoconus
Corneal distortion increases and corneal changes typical of keratoconus can be observed. As the vision quality with spectacles decreases, rigid gas permeable contact lenses become the option for better quality vision.
The rigid gas permeable contact lens covers the corneal irregularity with a regular hard surface and neutralises 90% of the corneal distortion. The focussing power of the contact lens can also compensate for any myopia, hyperopia and astigmatism resulting in better contrast, substantially reduced ghosting and flaring and overall much clearer vision.
Rigid gas permeable lenses are available in many diameters form 8.0mm up to 20.0mm in a miniscleral form. Hybrid lenses - RGP centre with a soft surround - can also give excellent vision with good comfort and stability. A new form of soft lens (KeraSoft) may also be effective in some cases.
Emergency spectacles can still be very useful as a back-up if an eye irritation arises or with lost lenses, even though the vision may not be 100%. Regular reviews are also essential to check that there has been no progression of the keratoconus, to check that the rigid gas permeable contact lenses are still fitting well, are in good condition, that the vision is stable and that the eye is healthy.
Advanced keratoconus
Substantial corneal distortion with moderate keratoconic corneal changes, slight to moderate corneal scarring present. Contact lens fitting as for moderate keratoconus except that there may be greater changes in the rigid gas permeable contact lens design, often using much steeper inside curvatures to maintain an appropriate fitting. Large miniscleral or scleral rigid gas permeable contact lenses may also be useful in unusually shaped corneae as they vault the cornea and improve stability and comfort.
Severe keratoconus
Dramatic corneal distortion, substantial corneal scarring and thinning. Often there is poor vision with rigid gas permeable contact lenses, substantially reduced contact lens tolerance and usually very difficult to fit an acceptable rigid gas permeable contact lens. Referral to an experienced corneal surgeon is recommended for consideration of a corneal transplant.