Keratoconus: Definition, Symptoms, Causes and Treatment Methods

What is Keratoconus?

Keratoconus is derived from the Greek words Kerato (cornea) and Konos (cone). Although it was first described as a corneal disease by Mauchart in 1748, its differentiation from other corneal ectatic conditions and detailed description of its clinical characteristics were made by John Nottingham in 1854.

Keratoconus is an idiopathic, non-inflammatory progressive disease characterized by the assumption of an irregular conical shape and thinning of the central and paracentral cornea. Keratoconus is the most common primary corneal ectatic disease. Although corneal thinning is most commonly seen in the central and inferior regions, involvement in the superior quadrants has also been documented. The disease, which typically presents with bilateral and asymmetric involvement, causes irregular astigmatism and myopia, resulting in decreased visual acuity. The prevalence in the population varies depending on geographic location, ethnic origin, and diagnostic criteria used, but is generally 1/2000. Keratoconus, which typically manifests in the second and third decades of life (10-20 years of age) and shows progression, becomes stable in the 30s to 40s.

What Are the Causes of Keratoconus?

The protrusion of the thinned corneal area causes irregular astigmatism and myopia, leading to decreased visual quality. Although generally beginning during adolescence (average onset age 16) in the second decade of life, earlier or later disease onset has also been reported. Its progression is highly variable and tends to be higher in younger individuals. Disease progression occurs most frequently between ages 10-20. It is less common between the second and third decades and unlikely after age 30. Eye rubbing has been identified as an important risk factor in disease progression.

Although keratoconus is often observed in isolation, it has been shown that it can accompany other diseases. It may be associated with systemic conditions such as Down syndrome, Turner syndrome, Ehlers-Danlos syndrome, Marfan syndrome, atopy, and osteogenesis imperfecta, and can also be accompanied by ocular diseases such as vernal keratoconjunctivitis, Leber's congenital amaurosis, retinitis pigmentosa, blue sclera, aniridia, and ectopia lentis.

Keratoconus generally affects both eyes; in almost all cases, involvement is bilateral, at least at the topographic level. Unilateral disease has been reported in only 14% of cases. The disease usually begins in one eye and can be seen in the other years later, particularly with the highest risk within the first 6 years following onset.

What Are the Symptoms of Keratoconus?

The symptoms of keratoconus vary depending on disease severity, but patients' initial complaints are generally decreased corrected visual acuity in one or both eyes, ocular irritation, and the need to frequently change glasses or contact lenses.

Although corneal topography plays an important role in disease diagnosis, early clinical recognition, combined with appropriate management, may contribute to better visual outcomes for some patients.

Advanced keratoconus has 2 macroscopic signs. These findings occur as the forward protruding cornea in advanced keratoconus pushes the lower eyelid forward in downward gaze, creating a V-shape. Light directed onto the cornea from the temporal side falling beyond the nasal limbus due to high astigmatism and steep corneal curvature is a finding seen in advanced keratoconus.

How Is Keratoconus Diagnosed?

Keratometry is a useful tool for demonstrating irregular astigmatism. With the use of corneal topography devices, keratoconus can now be diagnosed at much earlier stages, and these devices are widely used for diagnosing and monitoring keratoconus.

Placido disk-based corneal topography is currently one of the most commonly used devices for keratoconus diagnosis and can support diagnosis even before symptoms appear. Numerous numerical topographic indices have been determined to demonstrate keratoconic patterns on corneal topography, and these indices have high sensitivity and specificity in supporting the keratoconus diagnosis.

Keratoconus must be differentiated from conditions such as pellucid marginal degeneration, Terrien's marginal degeneration, and keratoglobus, which cause corneal steepening and irregular astigmatism and can lead to non-inflammatory central corneal scarring.

What Is the ICD Code for Keratoconus?

Keratoconus is a progressive eye disease that affects corneal shape and causes visual disturbance. Correct diagnosis and coding of this condition are important for proper medical billing and record keeping. In the past, the International Classification of Diseases, 9th Revision (ICD-9) was used to classify keratoconus. The ICD-9 code for keratoconus is 371.60.

However, it should be noted that the ICD-9 system has become outdated and has been replaced by the ICD-10 coding system. The ICD-10 code for keratoconus is H18.6. This new coding system provides more specific and detailed codes for various eye diseases, including keratoconus.

Correct coding of keratoconus is important for proper medical billing and documentation. This ensures that healthcare providers receive appropriate reimbursement for their services and facilitates accurate tracking of the prevalence and treatment outcomes of this condition.

In conclusion, while the ICD-9 code for keratoconus is 371.60, the transition to the ICD-10 coding system, which offers more precise codes for this eye disease, should be remembered.

What Are the Treatment Methods for Keratoconus?

The most important factor determining treatment management in keratoconus is disease severity and stage. The goal of treatment is to help prevent progression and support visual acuity where possible; outcomes may vary between individuals. For this purpose, early stage cases can be monitored with glasses and contact lenses, while moderate and advanced stage patients often require surgical methods such as keratoplasty, intracorneal ring segments, corneal collagen cross-linking, intraocular lens implantation, and laser treatments. Treatment decisions should be made in consultation with an ophthalmologist based on individual disease characteristics.

In early stages of keratoconus and forme fruste keratoconus (subclinical keratoconus), correction with glasses may be initially sufficient, but as the disease progresses, adequate visual acuity can no longer be achieved with glasses due to increasing irregular astigmatism.

Another treatment method used in early and moderate stages of keratoconus is the application of contact lenses. The goal of contact lens application is to cover the anterior surface of the ectatic cornea, whose optical properties are impaired due to irregular astigmatism, thereby creating a more regular spherical anterior surface. Contact lenses are not a treatment modality that prevents disease progression.

Corneal Collagen Cross-linking Treatment

Research on the etiopathogenesis of keratoconus has shown that the number of crosslinks between collagens is decreased, collagen fiber diameters are reduced, and corneal mechanical resistance is weakened. Based on this knowledge, corneal collagen cross-linking treatment, developed from these findings, is currently used relatively widely. This treatment modality aims to increase the number of crosslinks between collagen fibers in the corneal stroma, particularly in cases of progressive keratoconus, with the goal of making the cornea more rigid and regular, and thereby helping to stop or reduce progression; results may vary between patients.

The average treatment depth is 320 micrometers, and after treatment, the cornea must have a thickness of at least 400 microns after epithelial removal to protect against possible endothelial damage. In long-term studies conducted on patients who underwent corneal cross-linking, a decrease in average keratometry values, approximately 2.5 D reduction in average spherical equivalent, improvement in corrected visual acuity, improvement in morphologic symmetry, and reduction in corneal aberrations were reported topographically; individual results may vary, and patients are advised to consult their ophthalmologist for guidance specific to their condition.