Keratoconus is a disorder causing progressive thinning of the cornea. Patients usually present in adolescence or early twenties with blurred vision. An optician will pick up high or increasing astigmatism and refer the patients to the Hospital Eye Service. In addition to blurring of vision, patients may see multiple images, ghosting of images and be abnormally light sensitive. Keratoconus occurs in about 1 in 2000 people and is more common in people of Asian extraction. A family history of keratoconus is present in about 8% of patients.
The underlying cause is unknown, although a defect in the collagen fibrils making up the cornea is likely. A decrease in the number of cells (keratocytes) in the corneal stroma has been reported, the sigificance of which is uncertain.
An ophthalmologist will diagnose keratoconus from corneal changes observed at the slit-lamp and by measuring the shape of the cornea using corneal topography.
Most patients only need glasses to correct their astigmatism. As this increases, patients may require gas-permeable contact lenses to see clearly. These are semi-rigid and need a bit of time to get used to. The reason they work better than soft lenses is that light is refracted by the rigid front end of the lens (which doesn’t mold to the irregular corneal surface like a soft lens) and the corneal irregularities behind the lens are filled in by tears. Unfortunately, not everyone can tolerate gas-permeable lenses. Alternatives at this stage include Intacs Ring Segments and corneal graft surgery. This may be either partial thickness (deep anterior lammellar graft) or full-thickness (penetrating keratoplasty). The latter generally results in better vision but carries a greater theoretical risk of rejection. Newer treatments which offer to stabilise the shape of the cornea (corneal cross-linking treatment) are becoming available and may reduce the need for corneal graft surgery. Our experience of these is currently limited, but they show great promise.
Factors at presentation predicting likelihood of corneal graft
i) Young age at presentation (15% for patients 40 years old and younger)
ii) Steeper cornea (28% for eyes with a steep keratometric value greater than 52 diopters)
iii) Worse visual acuity (33% for visual acuity less than 6/12)
iv) Presence of corneal scarring (24%)
v) Contact lens discomfort
Overall, 12% of newly diagnosed patients followed for 8 years required corneal graft surgery (American Journal of Ophthalmology 2006).