Keratoconus is a common, non-inflammatory eye condition that typically begins affecting people in their teens or early twenties. It involves a progressive change in the shape of the cornea, the clear, dome-shaped front surface of the eye. The disorder causes the cornea to thin and gradually bulge outward into a cone shape. This alters the eye’s ability to focus light correctly, leading to visual distortion. This article addresses the primary concern for those diagnosed: the true risk of severe vision loss.
What Is Keratoconus?
Keratoconus is a progressive corneal disorder characterized by the thinning and steepening of the corneal structure. The normally smooth, dome-like surface warps, resulting in irregular astigmatism. This irregular shape prevents light from focusing sharply onto the retina, reducing visual clarity.
Patients commonly experience distorted or blurred vision, often requiring frequent changes in eyeglass prescriptions. Other symptoms include increased sensitivity to light (photophobia) and the appearance of glare or halos around light sources. While the exact cause is not fully understood, it is thought to involve a combination of genetic predisposition and environmental factors, such as vigorous eye rubbing.
The Direct Answer: The Risk of Severe Vision Loss
Keratoconus does not typically result in absolute blindness, which is the total loss of light perception. The condition affects the cornea, not the optic nerve or retina, which are the structures involved in true blindness. However, if left unmanaged or if it progresses rapidly, keratoconus can lead to severe visual impairment or functional blindness.
Functional blindness means vision cannot be corrected enough to perform necessary daily tasks, sometimes meeting the threshold for legal blindness. This severe loss is almost always attributed to extensive corneal scarring in advanced stages. With modern diagnostic techniques and treatment options, this severe outcome is largely preventable.
Stages of Visual Deterioration and Scarring
The progression of keratoconus is typically categorized into stages, reflecting the degree of corneal change and visual deterioration. In the early stage, vision changes are subtle and often correctable with standard glasses or soft contact lenses. As the condition advances to the moderate stage, thinning becomes more pronounced, requiring specialized vision correction like rigid gas permeable (RGP) or scleral contact lenses.
Progression to an advanced stage involves significant corneal steepening and thinning, making vision correction extremely challenging. The constant outward pressure can lead to a breakdown in the corneal structure, resulting in scarring. This scarring is the main cause of irreversible vision loss because it makes the cornea opaque, blocking light from entering the eye.
A rare, severe complication is acute corneal hydrops, where a tear in the inner corneal layer allows fluid to rapidly enter and swell the cornea. This causes sudden, dramatic vision loss and subsequent scarring.
Modern Treatment Options for Halting Progression
The goal of modern management is to halt disease progression and restore the best possible functional vision. For mild to moderate keratoconus, initial treatment involves specialized contact lenses that mask the irregular corneal surface. Scleral lenses, which vault over the entire cornea, are often preferred, offering superior comfort and clarity compared to traditional RGP lenses.
The most impactful intervention for stabilizing the cornea is Corneal Cross-Linking (CXL). This minimally invasive procedure uses riboflavin eye drops and ultraviolet-A light to create new bonds within the corneal collagen fibers. CXL effectively stiffens the tissue, stopping progressive thinning and bulging, and preventing the disease from reaching the stage where scarring causes vision loss.
For patients with significant shape irregularity but clear corneas, Intrastromal Corneal Ring Segments (Intacs) can be implanted. These tiny plastic rings are inserted into the mid-layer of the cornea to flatten and reshape the cone. If keratoconus is diagnosed too late and extensive scarring has severely compromised vision, a corneal transplant becomes necessary.
Transplant options include a full-thickness transplant, Penetrating Keratoplasty (PKP), and the partial-thickness Deep Anterior Lamellar Keratoplasty (DALK). DALK is often preferred because it replaces only the diseased front layers, reducing the risks associated with tissue rejection. Since the widespread adoption of CXL, the percentage of patients needing a corneal transplant has dramatically decreased.