Causes and risk factors
The exact cause of keratoconus is unknown. Genetic, structural, and environmental factors are responsible for this condition. Keratoconus runs in the family. It is a common finding in identical twins. The condition is associated with genetic abnormalities like Down’s syndrome, Marfan’s syndrome, Turner’s syndrome. It is also associated with diseases like atopic dermatitis, ectopia lentis, vernal conjunctivitis, retinitis pigmentosa, blue sclera. The condition usually starts around puberty.
Clinical presentation
The condition usually starts around puberty. It progresses slowly. The involvement is bilateral, but asymmetrical. Initial symptom is impaired vision. There is irregular retinoscopic reflex. There is thinning of central cornea with protrusion just below and nose to the centre. When patient looks down, there is bulging or tenting of the lower lid. This sign is called as Munson’s sign. In moderate cases, night vision is poor. There is photophobia. Multiple images is a common feature, also called as ghost images or monocular polyopia. Person sees halos around light sources. Streaks of light are seen. Symptoms become worse in low lights due to pupillary dilatation. Noticeable corneal abnormalities develop in this stage. Corneal nerves become prominent. Scarring, thinning, and shape deformity can be seen easily on eye examination. Epithelial iron deposition at the base of cone is seen. This is known as Fleischer’s sign. In advanced cases, considerable vision loss is observed.
Investigation
Medical history by the patient and clinical examination by the ophthalmologist helps in diagnosis. Ophthalmic tests include keratometry [measurement of corneal curvature with the help of keratometer]. Videokeratography/corneal topography [three-dimensional mapping of curved surface of cornea] is done. Tests to detect extent of visual impairments and refractive errors. Retinoscopy is recommended. Slit lamp biomicroscopy examination [to obtain stereoscopic magnified view of eye structures] is advised.
Treatment
In early stages of keratoconus, vision problems can be corrected by use of soft contact lenses and spectacles. If contact lenses prove inefficient, after some time there is necessity for rigid gas-permeable lenses. A piggyback contact lens is effective. Surgical treatments for keratoconus include penetrating keratoplasty; CXL or collagen cross-linking is a procedure to correct collagen fibre weakening and hence used to stabilize the progress of keratoconus; deep anterior lamellar keratoplasty [DALK] and intrastromal corneal ring placement [INTACS] help in treating the condition; corneal transplant may be helpful in the treatment.
