The cornea is the transparent, dome-shaped outer layer at the front of the eye, responsible for bending and focusing light onto the retina. The term “ectasia” describes a group of conditions where this clear window progressively weakens, thins, and begins to bulge outward. This structural change distorts the cornea’s shape from a smooth dome into an irregular, often cone-like, protrusion.
An effective analogy is to think of the cornea as a tire wall; if a spot weakens, the internal pressure can cause it to bulge. In corneal ectasia, the weakened tissue can no longer withstand the normal pressure inside the eye, impairing its focusing power. This condition affects both eyes, though the severity and rate of progression can differ between them, resulting in a gradual decline in vision.
Causes and Risk Factors
Corneal ectasia arises from a combination of genetic, environmental, and sometimes surgical factors that compromise the cornea’s structural integrity. The most common form is keratoconus, a primary ectasia with a genetic basis that often manifests during puberty or early adulthood. Other primary forms include Pellucid Marginal Degeneration, characterized by thinning in the lower periphery of the cornea, and Keratoglobus, a rarer condition where the entire cornea thins and takes on a more globular shape.
Chronic and vigorous eye rubbing is strongly associated with the development and progression of ectasia. This mechanical stress is believed to weaken the corneal tissue over time, particularly in individuals with underlying susceptibilities like allergies. A different category, iatrogenic ectasia, can occur as a rare complication of refractive surgeries like LASIK or PRK. If too much tissue is removed or the remaining cornea is too thin, it can become structurally unstable.
Certain systemic disorders, such as Down syndrome and connective tissue diseases like Ehlers-Danlos syndrome, are also associated with an increased risk due to inherent weaknesses in the body’s collagen.
Symptoms and Diagnosis
The initial symptoms of corneal ectasia are often subtle, beginning with a gradual blurring and distortion of vision. Sufferers may notice frequent changes in their eyeglass prescription, with a steady increase in astigmatism that standard lenses struggle to correct. As the cornea’s shape becomes more irregular, people often experience ghosting, halos around lights, or multiple images from a single light source (monocular polyopia). Heightened sensitivity to light can make activities like night driving particularly challenging.
An ophthalmologist can diagnose corneal ectasia through a comprehensive eye examination, starting with a slit-lamp inspection of the cornea. The definitive diagnosis relies on corneal topography and tomography, which create detailed three-dimensional maps of the cornea’s structure. Topography provides a color-coded map of the surface to reveal the characteristic steepening and irregular shape. Tomography measures the thickness of the cornea (pachymetry) to identify the precise areas of thinning.
Non-Surgical Vision Correction
For many individuals, managing the condition begins with non-surgical methods aimed at improving vision. In the early stages, eyeglasses may provide adequate correction, but they become less effective as the cornea grows more irregular. As the condition progresses, specialized contact lenses become the primary method for vision correction. Rigid gas permeable (RGP) lenses are a common option made of a firm material that holds its shape on the eye. They create a new, smooth refractive surface over the irregular cornea, neutralizing distortions and providing much clearer vision.
For those who find RGP lenses uncomfortable or have more advanced ectasia, scleral lenses offer another solution. These are large-diameter lenses that vault completely over the cornea, resting on the less sensitive white part of the eye, the sclera. This design creates a fluid-filled reservoir that masks surface irregularities and keeps the cornea hydrated, often resulting in exceptionally sharp vision.
Hybrid contact lenses attempt to combine the benefits of both. These lenses feature a rigid central zone for crisp optics, surrounded by a soft outer skirt, aiming to deliver the clear vision of an RGP lens with the comfort of a soft lens.
Procedural and Surgical Treatments
When non-surgical options are insufficient or the disease is progressing, procedural and surgical interventions are considered. The primary goal of modern treatment is to first stop the condition from worsening. Corneal collagen cross-linking (CXL) is a minimally invasive procedure designed for this purpose. CXL strengthens the cornea by creating new bonds between its collagen fibers using riboflavin eye drops activated by ultraviolet A (UVA) light.
To improve vision by reshaping the cornea, surgeons may use intrastromal corneal ring segments (Intacs). These are small, crescent-shaped segments surgically placed within the cornea. The rings help to flatten the steep central cornea, which can reduce irregular astigmatism and improve visual acuity.
In advanced cases where the cornea is significantly scarred or too thin, a corneal transplant (keratoplasty) is the final option. A partial-thickness transplant known as Deep Anterior Lamellar Keratoplasty (DALK) is often preferred. In DALK, the surgeon preserves the innermost endothelial layer, which reduces the risk of graft rejection compared to a full-thickness transplant.