Keratoconus is an eye condition where the cornea, the clear, dome-shaped front surface of the eye, progressively thins and bulges outward into a cone shape. This structural change warps the eye’s focusing surface, leading to distorted vision, irregular astigmatism, and increased nearsightedness. The condition typically begins in the late teens or early twenties and can worsen over 10 to 20 years. This change in shape causes light entering the eye to be incorrectly focused on the retina, resulting in blurred and distorted sight.
There is currently no medical treatment that reverses the physical thinning and restores the cornea to its original, healthy shape. However, modern ophthalmology offers several effective strategies to manage the condition and prevent further vision loss. These interventions focus on stabilizing the cornea’s structure and providing clear vision through specialized optical devices or surgical procedures. The goal is to halt the disease’s progression and maintain the highest possible visual acuity.
Interventions to Halt Disease Progression
The most significant advance in the management of Keratoconus is Corneal Cross-linking (CXL), a procedure designed to stop the condition from advancing. CXL works by strengthening the collagen fibers that make up the cornea’s central structure.
The procedure involves applying a solution containing riboflavin, a form of Vitamin B2, to the eye. Once the riboflavin has saturated the corneal tissue, the eye is exposed to controlled ultraviolet-A (UV-A) light. This combination activates the riboflavin, generating new chemical bonds, or “cross-links,” between the collagen molecules. Increasing these stabilizing bonds makes the cornea physically stiffer and more resistant to progressive thinning and bulging.
CXL is recommended for patients who show evidence of progressive Keratoconus, meaning their corneal shape is actively worsening. The procedure’s primary outcome is the stabilization of the cornea, preventing further deterioration of vision. While the treatment cannot reverse existing damage, it is a powerful tool to preserve the current level of vision. Early intervention, particularly in younger patients, is a priority to maximize the long-term benefit of structural stabilization.
Non-Surgical Vision Correction
For many individuals with Keratoconus, the primary challenge is correcting the distorted vision caused by the irregularly shaped cornea. In the mildest cases, standard eyeglasses or soft contact lenses may be sufficient to correct mild nearsightedness and astigmatism. However, as the corneal irregularity progresses, the vision distortion becomes too complex for conventional lenses to correct effectively.
Specialized contact lenses are required because they create a new, smooth refractive surface over the irregular cornea, neutralizing the cone shape. Rigid Gas Permeable (RGP) lenses are a common option, as their hard material maintains a consistent, smooth front surface for light to pass through. The RGP lens vaults over the cone, with the space between the lens and the cornea filled with a tear film that smooths out the irregularity.
Scleral lenses are significantly larger than traditional contact lenses and rest on the white part of the eye, called the sclera, completely vaulting over the sensitive, cone-shaped cornea. This design provides superior comfort and a stable reservoir of fluid between the lens and the eye, which helps to correct advanced irregular astigmatism. Hybrid lenses combine a rigid center for clear vision with a soft skirt for enhanced comfort, offering a balance between the visual clarity of RGP lenses and the comfort of soft lenses.
Addressing Advanced Disease Through Surgery
When the cornea has progressed to a point where specialized contact lenses no longer provide sufficient vision, or if significant scarring has occurred, surgical options become necessary. One technique is the insertion of intrastromal corneal ring segments, commonly known as Intacs. These are small, arc-shaped plastic inserts placed within the middle layer of the cornea.
The purpose of Intacs is to physically reshape the cornea by flattening the central cone, which improves the overall curvature and can make the eye more amenable to vision correction with contact lenses or glasses. This procedure can improve vision in corneas that are not yet severely thinned or scarred. However, the most definitive surgical intervention for advanced Keratoconus is a corneal transplant, also known as keratoplasty.
There are two main types of corneal transplants used for Keratoconus: Penetrating Keratoplasty (PKP) and Deep Anterior Lamellar Keratoplasty (DALK). PKP involves replacing the entire diseased cornea with a full-thickness donor cornea. DALK is a partial-thickness transplant that replaces only the front layers of the cornea, preserving the innermost layer and offering a lower risk of graft rejection. While a transplant can restore sight, patients often still require specialized contact lenses after surgery to achieve their best visual outcome.