What is Keratoconus ?
Keratoconus is derived from the Greek words Kerato (cornea) and Konos (kon) and was first defined as a disease of the cornea by Mauchart in 1748, its distinction from other ectatic conditions of the cornea and a detailed description of its clinical features were made by John Nottingham in 1854.
Keratoconus is an idiopathic, non-inflammatory progressive disease characterized by irregular conical shape and thinning of the central and paracentral parts of the cornea. Keratoconus is the most common primary corneal ectatic disease. Although corneal thinning is frequently seen in the central and inferior regions, involvement in the superior quadrants has also been described. The disease, which usually progresses with bilateral and asymmetrical involvement, causes irregular astigmatism and myopia, resulting in decreased visual acuity. Its incidence in the population varies according to geographical location, ethnicity and the criteria used in the diagnosis, but it is generally 1/2000. Keratoconus, which usually occurs between the ages of 10-20 and progresses, becomes stable at the age of 30-40.
What are the Causes of Keratoconus?
Protrusion of the thinned corneal area leads to irregular astigmatism and myopia, resulting in a decrease in visual quality. Although it generally starts with adolescence (mean age of onset 16) in the second decade of life, earlier or later disease development has also been reported. Its progression is highly variable, and this rate tends to be higher in younger individuals. The progression of the disease occurs mostly between the ages of 10-20. It is less common between the second and third decades and is unlikely over the age of 30. Eye rubbing has certainly been shown to be an important risk factor in progression.
Although keratoconus is often observed in isolation, it has also been shown that it can accompany other diseases. Keratoconus generally involves both eyes. In almost all cases, the involvement is bilateral, albeit only at the topographic level. Unilateral disease was reported in only 14% of cases. The disease usually starts in one eye and can occur years later in the other, with the highest risk in the first 6 years after onset.
Keratoconus generally involves both eyes.In almost all cases, the involvement is bilateral, albeit only at the topographic level. Unilateral disease was reported in only 14% of cases. The disease usually starts in one eye and can occur years later in the other, with the highest risk in the first 6 years after onset.
What Are the Symptoms of Keratoconus?
Although the symptoms of keratoconus vary depending on the severity of the disease, the initial complaints of the patients are usually decreased corrected visual acuity in one or both eyes, ocular irritation and the need to change glasses or contact lenses at frequent intervals.
Although corneal topography plays an important role in the diagnosis of the disease, early diagnosis by clinical signs, together with appropriate management, can significantly improve visual outcome.
Advanced keratoconus has 2 macroscopic manifestations. This finding indicates that the cornea protruding anteriorly in advanced keratoconus, It is the name given to pushing the lower eyelid forward and revealing a V shape in the downward gaze position. It is a symptom of advanced keratoconus, where the light falling from the temporal to the cornea falls beyond the nasal limbus due to high astigmatism and steep corneal inclination.
How Is Keratoconus Diagnosed?
Keratometry is a good tool for demonstrating irregular astigmatism. With the use of corneal topography devices, keratoconus can be diagnosed at much earlier stages, and these devices are very successful in the diagnosis and follow-up of keratoconus.
Placido disc-based corneal topography is the most commonly used device in the diagnosis of keratoconus today, and it can diagnose even before symptoms appear. Many numerical topographic indices have been determined to show the keratoconic pattern in corneal topography, and these indices have high sensitivity and specificity in diagnosing keratoconus.
Differential diagnosis of keratoconus should be made with diseases such as corneal steepening and irregular astigmatism, pellucid marginal degeneration, terrien marginal degeneration and keratoglobus that can cause non-inflammatory central corneal scarring.
What are Keratoconus Treatment Methods?
The most important factor determining the treatment management in keratoconus is the severity and stage of the disease. The goal of treatment is to prevent progression and, if possible, to achieve good visual acuity. For this purpose, early-stage cases can be followed with glasses and contact lenses, while patients in the middle and advanced stages often need surgical methods such as keratoplasty, intracorneal ring segments, corneal cross-linking, intraocular lens applications and laser treatments.
In the early stages of keratoconus and forme fruste keratoconus (subclinical keratoconus), correction with glasses may be sufficient initially, but when the disease progresses, adequate visual acuity cannot be achieved with glasses due to the increase in irregular astigmatism.
The purpose of applying contact lenses, which is another method used in the treatment of keratoconus in the early and middle stages, is to provide a more regular spherical anterior surface by covering the anterior surface of the ectatic cornea, whose optical properties are impaired due to irregular astigmatism. Contact lenses are not a treatment modality that prevents disease progression.
Corneal Collagen Crosslinking Treatment
Studies on the etiopathogenesis of keratoconus have shown that the number of cross-links between collagens decreases, the diameters of collagen fibers decrease, and the mechanical resistance of the cornea weakens. Collagen cross-linking treatment, which was developed based on this information, is widely applied today. With this treatment modality, especially in progressive keratoconus cases, it is aimed to increase the number of cross-links between the collagen fibers in the stroma of the cornea and to make the cornea more rigid and regular, as a result of which the progression can be stopped or at least reduced.
The average treatment depth is 320 micrometers, and a cornea of at least 400 microns thick is required after epithelial peeling to avoid possible endothelial damage after treatment. In a long-term study on patients with corneal crosslinking, a decrease in the mean spherical equivalent of approximately 2.5 D, an increase in best corrected visual acuity, an improvement in morphological symmetry, and a decrease in corneal aberrations were found, together with a decrease in topographically average keratometry values.
Prof.Dr. Ergün Dağlıoğlu (Eğitim Görevlisi), Beyin Cerrahı, Beyin Ve Sinir Cerrahisi