The cornea is the clear front part of the eye that covers anterior chamber. The optical power of the eye depends on the degree to which the structures of the eye converge the light focusing it on the retina. The normal eye has the optical power of 60 diopters (D), 43 of which are provided by the cornea. The change of the shape of the cornea disturbs the process of light refraction and leads to vision impairment.
The cause of the disorder is not known, although several factors may be involved. An imbalance of the enzymes in the cornea causes damage to the connective tissues by the free radicals. Keratoconus occurs when the connective tissues of the eye are weak and the cornea progressively thins failing to hold the normal shape. Genetic predisposition is suggested as the condition is more common for persons who have a family history of keratoconus.
Keratoconus is more likely to occur among those whose relatives have the same condition. The disorders of the connective tissues are also associated with keratoconus such as Marfan syndrome, exposure to ultraviolet rays, eye rubbing and chronic irritation of the eye. Keratoconus is more frequent among Asian descendants.
Keratoconus affect one or both eyes and commonly begins when a person is in the teenage years or early 20s. The thinning of the cornea causes its bulging outwards. The vision impairment develops gradually, each eye may be affected differently.
The first symptoms of the condition are nearsightedness, slight blurring, distorted vision and sensitivity to light. A halo around lights may appear, affected persons experience eye pain and headache. In later stages the vision is distorted even more, the person has astigmatism and is not able to wear contact lenses, because they are not fitting the eye’s shape. The cornea can swell and later the scarring occurs.
[See also:Thyroid eye disease]
Examination with a help of the slit lamp is performed to evaluate the diagnosis of keratoconus.
1. In the early stages the condition may be corrected with the help of the eyeglasses or contact lenses. The progression of the disease requires other methods of treatment.
2. Custom soft contact lenses were designed to fit the shape of the one’s cornea based on the measurement of the person’s eye.
3. permeable contact lenses may be the treatment option when the soft contact lenses are unable to control the keratoconus.
4. To provide better fitting the “piggybacking” contact lenses are used. This implies a soft contact lens made of silicone hydrogel worn under the gas permeable lens.
5. Scleral and semiscleral lenses cover only a part of the cornea.
6. The corneal cross-linking (CXL) is performed to strengthen the tissues of the cornea. Two variants of CXL are known. Epithelium-off CXL implies the removal of the epithelium (outer layer of the cornea) that allows vitamin B2 to get into the cornea. The epithelial-on method or transepithelial CXL implies the penetration of the riboflavin into the cornea without removal of the epithelium. This method is harder to perform, although it is associated with the lessen risk of the side-effects.
7. Intacts are corneal inserts placed in the mid-layer of the cornea. This method is recommended when the lenses are not able to maintain vision anymore.
8. Topography-guided conductive keratoplasty help to smooth the bulging of the cornea.
9. Corneal transplant or penetrating keratoplasty is used in the late stages of keratoconus or when a person can’t tolerate the lenses.