What is keratoconus?
Keratoconus is a disorder of the cornea – the transparent ‘front window’ of the eye in which the normally round, dome-like cornea becomes thin and develops a cone-like bulge. Keratoconus literally means “cone-shaped cornea. This abnormal shape prevents the light entering the eye from being focused correctly on the retina and causes distortion of vision. Keratoconus can make some activities difficult, such as driving, typing on a computer, watching television or reading in severe cases.
In its earliest stages, keratoconus causes slight blurring and distortion of vision and increased sensitivity to glare and light. These symptoms usually appear in the late teens or late 20s affecting men and women. Keratoconus may progress for 10-20 years and then slow in its progression. One or both eyes may be affected differently. The main symptom is blurred vision even in glasses. The glasses prescription increases with time and usually shows high levels of myopia (short sight) and astigmatism. It is not possible to predict whether keratoconus will be progressive or at what rate it will worsen but in general the younger the age and the more severe the disorder when it begins, the more rapidly it is likely to deteriorate. In advanced cases ‘hydrops’ can occur: this is the sudden onset of discomfort, redness and reduced vision caused by a split in the inside of the cornea that leads to swelling. It usually clears after a few weeks but may leave permanent scarring.
In most cases of keratoconus, the cause is unknown. Keratoconus is usually not inherited, although there are exceptions, and is not lifestyle-related, although persistent heavy eye rubbing may be a risk factor. It is slightly more frequent in patients with severe asthma or eczema and patients with chromosomal disorders such as Down’s syndrome.
The protrusion on the cornea may be seen with a slit lamp microscope. Retinoscopes and keratometers are used for prescribing glasses and contact lenses. In keratoconus, they show abnormal readings. The cornea topographer is the most important diagnostic device which creates a map of the cornea surface and accurately measures the keratoconic protrusion. Pachymetry is also done to measure the thickness of the cornea.
Keratoconus treatment often depends on the severity of the symptoms. During early stages, vision can be corrected with eyeglasses or soft contact lenses. As the condition progresses, Rose K lenses which are rigid gas permeable contact lenses will be the primary treatment to correct vision adequately. The contact lenses must be carefully fitted accompanied by frequent checkups and lens change may be needed to achieve good vision. For many years, the only surgical treatment is a corneal transplant. A corneal transplant may be recommended only if good vision is no longer possible with other treatments.
The following newer technologies may delay or prevent the need for a corneal transplant:
- High-frequency radio energy (conductive keratoplasty) to change the shape of the cornea so contact lenses work better.
- Corneal implants (Intacs) which are small curved implantable corneal devices that can help flatten the steep cornea found in keratoconus.
- An experimental treatment called corneal cross-linking uses a laser and eye drops to promote “cross-linking” or strengthening of the collagen fibers that make up the cornea. This treatment may flatten or stiffen the cornea, preventing further protrusion.
In most cases, vision can be corrected with rigid gas-permeable contact lenses. If a corneal transplant is needed, results are usually good. However, the recovery period can be long and patients often still need contact lenses for better vision.
There is a risk of rejection after corneal transplantation, but the risk is much lower than with other organ transplants.
Patients with mild or borderline keratoconus should not have LASIK, the most common type of laser vision correction. Corneal topography is done before LASIK to rule out people with this condition.