What Is Keratoconus?
Keratoconus is a progressive condition characterised by thinning of the cornea (the transparent layer at the front of the eye) and its forward bulging. It affects both eyes and is also known as “corneal cone.”
The cornea is the most important refracting layer of the eye. Changes in this region cause the light entering the eye to focus incorrectly, severely impairing vision quality. The disease is more common in people with a family history and in those with an allergic disposition. The most important symptom is a loss of vision that cannot be corrected with glasses.
Keratoconus usually starts in the mid-teens (15–16 years of age) and can continue to progress up to the age of 35. The course of the disease varies greatly from person to person. In the early stages the patient usually notices frequent changes in glasses prescription. As the disease progresses, glasses are no longer able to provide clear vision.
Treatment of Keratoconus
Because the course and rate of progression vary so much from one patient to another, the treatment of keratoconus is highly individualised.
Some patients see clearly without even needing glasses and are unaware of their condition, while others have a rapidly progressive form requiring a corneal transplant in their twenties.
Keratoconus is essentially a structural disease, so there is no definitive cure.
The aim of treatment is to bring patients to a level of vision that allows them to carry on their daily lives comfortably.
CCL — Corneal Cross-linking
Over the past five years, corneal cross-linking has been used with increasing frequency and is the technique that halts the progression of keratoconus. The treatment uses ultraviolet A light together with riboflavin (vitamin B2) to strengthen the structure of the cornea.
Whatever the stage of the disease and the patient’s level of vision, this is the first-line treatment whenever progression is documented. CCL not only stops keratoconus from progressing — in some patients it also produces a slight improvement in vision.
Procedure
After topical (drop) anaesthesia, the outermost layer of the cornea (the epithelium) is removed. Riboflavin solution is then applied every 5 minutes for 30 minutes. After that, 370 nm UVA light is applied to an area of approximately 8 mm at a distance of 4–5 cm from the corneal surface for 30 minutes.
During the UVA application, riboflavin drops are continued every 5 minutes. At the end of the procedure the eye is dressed with an antibiotic ointment.
The average recovery period is 2 days.
Contact Lenses
In keratoconus the shape of the cornea is distorted. In early keratoconus the mild astigmatism that develops can be corrected with soft lenses. As keratoconus progresses, even keratoconus-specific soft lenses can no longer improve vision.
For this reason semi-rigid, hybrid (rigid centre, soft periphery) and piggy-back (soft and semi-rigid lenses used together) contact lenses are used. However, contact lenses do not stop the progression of keratoconus. Patients using lenses must be followed up regularly and CCL treatment should be performed if necessary. After CCL the patient continues to wear contact lenses for good vision.
Intra-corneal Rings (Keraring, Ferrara Ring, Intacs)
These are transparent, biocompatible, glass-derivative implants that are inserted into the distorted corneal tissue of a keratoconus patient. As they are placed within the cornea they are not removed and reinserted like contact lenses.
They can remain in the eye without problem for the rest of the patient’s life, but can also be removed if necessary. Different brands and designs of ring segments are available, but they all work in the same way.
The aim is to make the distorted cornea more regular and ensure that the light entering the eye is correctly refracted.
Procedure
After topical anaesthesia, a femtosecond (Intralase) laser is used to create a tunnel at the desired depth and diameter within the cornea. This step takes about 10 seconds. The ring segments are then placed inside the cornea using special forceps. The eye does not need to be patched after the procedure.
We have been performing ring implantation in our clinic since 2006. Over the past few years we have combined this treatment with CCL, both stopping the progression of keratoconus and offering our patients an even better visual outcome.
Keratoplasty (Corneal Transplantation)
Keratoplasty is the option of choice in cases where the cornea has lost its transparency or where other treatments have failed. Although it is colloquially known as an “eye transplant,” keratoplasty is in fact a surgical procedure in which only the diseased cornea of the eye is replaced with a donor cornea.
In keratoplasty surgery, a 6–9 mm diameter circular piece is removed from the donor cornea and an equally sized piece is removed from the recipient’s cornea; the donor tissue is then sutured into place. The surgery is preferably performed under general anaesthesia.
Prepared by the Editorial Board of Eye Foundation Hospitals.
