Keratoconus is a progressive disorder where the normally dome-shaped, clear cornea thins and gradually bulges outward into a cone-like shape. This structural change distorts the path of light entering the eye, leading to blurred and significantly impaired vision. Treatment strategies focus on two primary objectives: stabilizing the cornea to halt progression, and rehabilitating vision by correcting the resulting irregularity.
Vision Correction for Early Stages
The initial management of Keratoconus begins with non-invasive methods aimed at correcting refractive errors caused by mild corneal irregularity. In the earliest stages, standard eyeglasses are often effective for correcting mild myopia and regular astigmatism. Traditional soft contact lenses may also be prescribed, offering a comfortable option for vision correction.
These conventional corrective measures compensate for visual symptoms like blurriness and distortion but do not address the underlying structural weakness of the cornea. Since soft lenses conform to the irregular corneal surface, their effectiveness diminishes quickly as the cone shape becomes more pronounced. Eyeglasses and standard soft contacts offer a temporary solution for visual acuity but cannot prevent the progressive thinning and bulging characteristic of Keratoconus.
Stopping Disease Progression
Corneal Cross-linking (CXL) is the only established procedure designed to halt the progression of Keratoconus by strengthening the corneal tissue. This intervention works by increasing the number of cross-links between the collagen fibers that make up the corneal stroma. The procedure involves saturating the cornea with riboflavin (Vitamin B2), which acts as a photosensitizer.
Once the riboflavin has penetrated the cornea, the tissue is exposed to controlled ultraviolet-A (UV-A) light. This light activates the riboflavin, initiating a photochemical reaction that forms new covalent bonds between the collagen molecules. The result is a significant increase in the cornea’s biomechanical rigidity, which effectively prevents further thinning and bulging. CXL is most beneficial when performed early to stabilize the cornea before significant vision loss occurs.
There are two main approaches to the CXL procedure: Epithelium-off (Epi-off) and Epithelium-on (Epi-on).
Epithelium-Off (Epi-off)
The traditional Epi-off method involves gently removing the cornea’s thin outer layer, the epithelium, to allow for optimal riboflavin penetration. This technique offers the most robust biomechanical strengthening. However, it results in post-operative discomfort, a risk of infection, and a longer healing period.
Epithelium-On (Epi-on)
The newer Epi-on, or transepithelial, technique preserves the epithelium, leading to faster recovery and less pain. However, the intact epithelium acts as a natural barrier, historically limiting the riboflavin’s depth of penetration and the overall stiffening effect. Advances in riboflavin formulations are aimed at improving the efficacy of Epi-on CXL to provide comparable long-term stability to the Epi-off procedure while maintaining the safety benefits.
Advanced Vision Rehabilitation
When the corneal shape becomes too irregular for standard corrective lenses, specialized devices are necessary to achieve functional vision.
Specialized Contact Lenses
Rigid Gas Permeable (RGP) contact lenses are a common next step. Their firm structure does not conform to the corneal cone; instead, the RGP lens rests on the eye, creating a smooth, tear-filled layer between the lens and the cornea. This layer neutralizes the surface irregularity, providing a sharp refractive surface for vision.
Hybrid contact lenses offer a compromise for patients who find RGP lenses uncomfortable, combining a rigid, high-Dk gas permeable center with a soft peripheral skirt. The rigid center provides the necessary visual correction, while the soft skirt enhances comfort and stability. Scleral lenses represent a significant advancement, featuring a large diameter that vaults entirely over the irregular cornea. These lenses rest on the less sensitive sclera, creating a fluid-filled reservoir that protects and hydrates the cornea while offering exceptional comfort and stable vision.
Intracorneal Ring Segments (Intacs)
Intracorneal Ring Segments, known as Intacs, are a minor surgical option for vision improvement. These tiny, arc-shaped plastic inserts are placed within the corneal stroma in the periphery of the cone. The implantation of these segments works to flatten and reshape the central cornea, which can reduce the severity of the cone and improve visual acuity. Intacs can often make the subsequent fitting of specialized contact lenses easier and more effective.
Surgical Intervention for Severe Cases
Corneal transplantation, or Keratoplasty, is reserved for advanced Keratoconus cases where the cornea is severely scarred, dangerously thin, or vision cannot be restored by less invasive means. This treatment involves replacing the diseased cornea with healthy donor tissue. The two most common forms of transplantation are full-thickness and partial-thickness procedures.
Penetrating Keratoplasty (PKP)
PKP is the traditional, full-thickness transplant where the entire central cornea is replaced with a donor graft. While effective, PKP carries a higher risk of complications, including immune-mediated graft rejection. The recovery period is extensive, often requiring many months for sutures to be removed and final vision correction to be achieved.
Deep Anterior Lamellar Keratoplasty (DALK)
A preferred alternative is Deep Anterior Lamellar Keratoplasty (DALK), a partial-thickness transplant. The surgeon removes the diseased corneal stroma but preserves the patient’s own innermost layer, the Descemet’s membrane and endothelium. Retaining the host’s endothelium significantly reduces the risk of immune rejection, which is the most serious complication of full-thickness transplants. DALK generally offers a safer procedure with a faster recovery of the eye’s surface integrity, though visual recovery can still be slow.