RISK FACTORS
Reported risk factors for keratoconus include eye rubbing, a family history of keratoconus, genetic predisposition, certain systemic disorders such as Down’s syndrome, ocular allergy, connective tissue disease, and long-term rigid contact lens wear. It is usually an inherited corneal disorder, often in an autosomal dominant fashion. This means that approximately 50% of family members may end up with it. But it also can be random with no other family members affected. It affects men and women in equal proportions and is bilateral in 90% of patients.
SYMPTOMS
At early stages, the symptoms of keratoconus may be no different from just having the need for spectacle correction. As the disease progresses, the vision deteriorates. Visual acuity becomes impaired at all distances, and night vision is sometimes quite poor. Some individuals have vision in one eye that is markedly worse than that in the other eye. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye. There is usually little or no sensation of pain. Keratoconus can cause substantial distortion of vision, with multiple images, streaking and sensitivity to light.
DIAGNOSIS
This is usually done by an ophthalmologist with a detailed eye examination. Diagnosing early keratoconus can be tricky, since mild disease often does not show any identifiable signs on slit-lamp examination; however, recent and a more definitive diagnosis can be obtained using corneal topography, in which an automated instrument projects an illuminated pattern onto the cornea and determines its shape from analysis of a digital image. The topographical map reveals distortions or scarring in the cornea, with keratoconus revealed by a characteristic steepness of curvature which is usually below or around the centre of the cornea. The topography record of the degree and extent of the deformation is used for assessing its rate of progression. Unilateral cases tend to be uncommon. Sometimes it’s a mild condition in the better eye, below the limit of clinical detection. It is common for keratoconus to be diagnosed first in one eye and not until later in the other.
At our hospital, we use a very sensitive Topography instrument called the ‘Topolyser’ from Wavelight Inc.
PROGRESS
However good the vision may be with the use of contact lenses, vision may be difficult to maintain at times as the condition progresses and contact lens tolerance varies. Contact lenses are used as temporary measures of treatment, but do not, unfortunately, slow down the rate of progression of the cone. In about 10% to 20% of keratoconus patients the cornea may become extremely steep, thin and irregular or the vision cannot be improved sufficiently with contact lenses. The cornea may then need to be replaced surgically with a corneal transplant or graft. Visual recovery after a transplant takes a long time - sometimes as long as a year to 18 months - to settle down and there is a strong possibility that the eye will still need to be fitted with a contact lens afterwards in order to see properly. Surgery is therefore not a shortcut to perfect vision and nor is it a way of avoiding contact lens wear.
There is also a risk of the transplant rejecting afterwards, although a majority of corneal transplants done for keratoconus are successful.
TREATMENT
Treatment of mild keratoconus is geared towards eliminating or reducing the myopia and astigmatism.
Temporary:
Permanent:
New modality of treatment:
- Corneal Collagen Crosslinking with Riboflavin (C3-R®*)
Contact lenses
Initial management is tried with rigid contact lenses by our contact lens specialist. In very early stages of keratoconus, spectacles can suffice to correct minor astigmatism. As the condition progresses, spectacles may no longer provide the patient with a satisfactory degree of visual acuity, and most doctors will move to managing the condition with contact lenses.
Rigid gas permeable contact lenses for keratoconus improve vision by means of tear fluid filling the gap between the irregular corneal surface and the smooth regular inner surface of the contact lens, thereby creating the effect of a smoother cornea.
Many specialized types of contact lenses have been developed for keratoconus, and our contact lens expert helps you with the best fit. The irregular cone needs expertise to produce a contact lens with optimal contact, stability and steepness. Some trial-and-error fitting might be necessary.
Traditionally, contact lenses for keratoconus have been the 'hard' or rigid gas-permeable variety, although manufacturers have also produced specialized 'soft' or hydrophilic contact lenses. A soft contact lens has a tendency to conform to the conical shape of the cornea, thus diminishing its effect. These do not however prove effective for every patient.
Some patients also find good vision correction and comfort with a "piggyback" contact lens combination, in which gas permeable rigid contact lenses are worn over soft contact lenses, providing clarity of vision and comfort.
Precaution with contact lenses: There is a small risk of infection when wearing contact lenses and the risk becomes much greater if the contact lenses are not kept clean, so it is important to strictly follow the hygiene instructions given when the contact lenses are fitted. |
