Keratoconus is a progressive eye condition characterized by a thinning and forward bulging of the cornea, the clear front surface of the eye, causing it to take on a cone-like shape. The physical changes to the cornea are permanent, meaning Keratoconus does not go away or get better on its own. It is a chronic condition that cannot be cured or reversed without intervention, but its progression can be stopped. The disease typically stabilizes naturally at some point in adulthood, or it can be halted much earlier through medical procedures. Modern treatment focuses on stabilizing the cornea to prevent further worsening and then correcting the resulting vision problems.
Understanding Disease Progression
Keratoconus typically begins to manifest during puberty or young adulthood, often in the teenage years or twenties. This progressive condition involves a weakening of the corneal stroma, which makes up the thickest layer of the cornea. The cornea is normally rich in a protein called collagen, which provides the structural strength to maintain its rounded shape.
In Keratoconus, this collagen structure weakens, and the internal pressure of the eye causes the cornea to thin and bulge forward, resulting in irregular astigmatism and increasing nearsightedness. The rate of progression is highly variable among individuals, but it is generally more rapid in younger people. The disease often affects both eyes, though one eye is usually more severely affected than the other.
The natural history of Keratoconus suggests that the progression phase usually lasts for 10 to 20 years. It tends to slow down and eventually stabilize, often by the late 30s or early 40s. Once the cornea stabilizes, the conical shape remains, but it stops getting steeper.
Stopping Disease Progression
The primary medical intervention designed to halt the progression of Keratoconus is Corneal Cross-Linking (CXL). This minimally invasive procedure strengthens the cornea by creating new bonds between the collagen fibers, preventing the cone shape from becoming steeper.
The procedure involves applying riboflavin, a form of Vitamin B2, onto the cornea, which acts as a photosensitizing agent. The eye is then exposed to controlled ultraviolet-A (UVA) light. This combination initiates a photochemical reaction that increases the number of cross-links, or connections, between the collagen molecules.
The formation of these new bonds increases the tissue’s mechanical rigidity and stiffness by up to 300%, fortifying the structure against further bulging. CXL is primarily a stabilization procedure, not a vision correction surgery. While some patients may experience slight visual improvement, its main purpose is to stop the disease from worsening. CXL is most effective when performed early, particularly in younger patients where the risk of rapid progression is highest.
Corrective Options for Vision
Once Keratoconus has stabilized, either naturally or through CXL, the focus shifts to correcting the remaining visual distortion. In the mildest stages, the irregular shape of the cornea can often be corrected adequately with standard eyeglasses or soft contact lenses. However, as the conical shape becomes more pronounced, these options are typically insufficient because they cannot counteract the irregular astigmatism.
For moderate to severe Keratoconus, specialized contact lenses are the next step in vision rehabilitation. These lenses vault over the irregular corneal surface, creating a new, smooth front surface for light to pass through. Rigid Gas Permeable (RGP) lenses are often used because they maintain their shape and provide the necessary smooth refractive surface.
Scleral lenses represent a significant advancement. These large-diameter lenses rest entirely on the white part of the eye (the sclera), arching over the entire cornea without touching the cornea. This design creates a fluid-filled reservoir between the lens and the cornea, which neutralizes the surface irregularities and provides significantly better vision correction.
In severe cases, when the cornea has become too thin, scarred, or the shape is too irregular for successful contact lens wear, a corneal transplant may be required. This involves surgically replacing the diseased cornea with healthy donor tissue. Procedures include a full-thickness transplant or a partial-thickness procedure like Deep Anterior Lamellar Keratoplasty.