Text author: Dr sc. Bojan Kozomara, dr med.
Keratoconus is the most common degenerative and progressive change of the cornea, characterized by non-inflammatory thinning of the corneal tissue, which takes on a conical shape. Its prevalence is 1:2000 individuals, being more common in males than in females. It occurs in all populations worldwide, although it is more prevalent in certain ethnic groups.
The exact cause of keratoconus is still unknown, but it is believed to be associated with poor enzymatic activity within the cornea itself. There is also a genetic predisposition, as it tends to occur more frequently in families where keratoconus has already been diagnosed.
The progression of keratoconus is faster in patients with Down syndrome. It is also believed that the disease usually affects both eyes, but one eye often has a more pronounced progression of the disease. It typically progresses in adolescence and then stabilizes (although this is not always the case).
Keratoconus can be classified into four stages (grades), with the first representing the mildest form of the disease and the fourth the most severe (often requiring corneal transplantation).
The primary symptom of keratoconus is a unilateral decrease in visual acuity due to progressive myopia (nearsightedness) and irregular astigmatism. The main sign is central and paracentral thinning of the corneal stroma (taking on a conical shape).
Treatment for mild to moderate cases of keratoconus involves wearing glasses and rigid gas-permeable or hard contact lenses, along with regular monitoring of disease progression. For progressive forms of the disease, corneal collagen cross-linking (CXL) is recommended. Patients who tolerate contact lenses well often have satisfactory vision, while those with advanced stages of keratoconus, unable to tolerate lenses, and with visual acuity below 30%, as well as those with pronounced corneal thinning, are candidates for surgical treatment. If corneal decompensation has occurred and it has irreversibly lost its transparency, corneal transplantation is the only method of choice for these patients. The best techniques used for diagnosing and monitoring the course of the disease are OCT (optical coherence tomography) of the anterior segment of the eye and Pentacam – computerized corneal topography.
Corneal collagen crosslinking (CXL) is a procedure aimed at strengthening weakened collagen bonds in the cornea to slow the progression of keratoconus. The emphasis is on the word “slow down” because the procedure has been used worldwide for about 20 years, so there is still not enough time elapsed to definitively determine whether crosslinking definitively halts the progression of keratoconus. According to current experiences, out of 5 patients who underwent this procedure, one eventually required corneal transplantation.
Individuals recommended for crosslinking are patients with keratoconus whose corneal thickness is not below 400 microns, patients with clear and unscarred corneas, and those with steep meridian corneal values of up to 58 diopters, while visual acuity with glasses can be 90% or lower. Patients with other corneal diseases, and of course pregnant patients, are not candidates for crosslinking.
The cross-linking procedure lasts about half an hour to 45 minutes. It is done under local anesthesia using drops and is completely painless. The corneal epithelial layer is gently removed from the surface of the cornea using a delicate instrument, and then the cornea is treated with high doses of vitamin B2 in the form of a thick liquid called Riboflavin for 20 to 30 minutes. Riboflavin serves a dual purpose here. Firstly, it strengthens the cornea, but equally importantly, it protects deeper segments of the eye from UV rays, which will later be applied to the eye during treatment. After the Riboflavin instillation is completed, the cornea is exposed to a UV lamp for the next half hour or 10 minutes (depending on the protocol being used), with breaks every five minutes. The lamp automatically switches off, and during a two-minute break, Riboflavin is instilled again. After the procedure, a soft contact lens is applied to the treated cornea, which remains in the eye continuously for 4 to 7 days. The patient receives local therapy in the form of corticosteroid drops to be instilled over the next two months. On the first day after the procedure, the patient may experience pain, which is duly warned about.
Actual results after crosslinking are evaluated 6 to 12 months post-procedure in adult patients, while in children, it may take up to 24 months. After recovery, the patient can continue wearing contact lenses, often with the same parameters as before crosslinking.
