Corneal ectasia is characterized by a progressive change in the shape of the cornea, the clear, dome-shaped front surface of the eye. This alteration involves a thinning and outward bulging of the cornea, which can significantly impair vision. Understanding this condition is important for anyone experiencing changes in their sight, as early recognition can influence management and treatment outcomes.
Understanding Corneal Ectasia
The cornea normally functions as the eye’s primary focusing lens, bending light rays precisely onto the retina to create clear images. In corneal ectasia, the structural integrity of the cornea weakens, leading to a gradual thinning and an irregular, cone-like protrusion of its surface. This change profoundly affects how light enters the eye.
As the cornea becomes distorted, vision can become increasingly blurred and distorted, often accompanied by irregular astigmatism. Individuals commonly report symptoms such as increased sensitivity to light (photophobia), halos or starbursts around lights, and double vision in one eye. Frequent and rapid changes in eyeglass prescriptions also occur.
Causes and Risk Factors
Corneal ectasia can arise from primary conditions or develop as a secondary consequence. The most common primary form is keratoconus, a progressive disorder where the cornea thins and bulges into a cone shape, typically beginning in adolescence or early adulthood. Pellucid marginal degeneration (PMD) is another primary type, characterized by a crescent-shaped band of thinning in the lower part of the cornea, often appearing in individuals in their 20s, 30s, or 40s.
Secondary ectasia frequently occurs following certain eye surgeries, particularly laser vision correction procedures like LASIK and PRK. These procedures reshape the eye by removing corneal tissue. If too much tissue is removed or the cornea is predisposed, its structure can weaken, leading to bulging. This post-surgical ectasia can manifest months to years after the procedure.
Other factors contribute to ectasia development or progression. Chronic eye rubbing is often associated, and a genetic predisposition exists, with higher incidence in those with a family history. Connective tissue disorders can also increase risk.
Diagnosing Corneal Ectasia
Identifying corneal ectasia involves a thorough examination by an eye care professional. The diagnostic process begins with a comprehensive eye exam and a detailed review of the patient’s medical and family history. A slit-lamp examination allows the doctor to visually inspect the cornea for signs of thinning or bulging, particularly in more advanced stages.
Specialized imaging tests detect ectasia, especially in its early or subclinical forms. Corneal topography maps the surface contour of the cornea, revealing irregularities that indicate ectasia. Corneal tomography, utilizing devices like the Pentacam or Orbscan, provides a more advanced three-dimensional reconstruction of the cornea, including detailed maps of its anterior and posterior surfaces and its thickness.
These tomographic maps detect subtle changes in the posterior corneal surface or localized thinning, which may precede visible anterior changes. Early detection through these techniques is important for timely intervention and better visual outcomes.
Treatment and Management Options
Managing corneal ectasia aims to correct vision and halt its progression. In early stages, vision correction may involve eyeglasses or specialized contact lenses. Rigid gas permeable (RGP) lenses can provide a smooth, regular optical surface over the irregular cornea, significantly improving vision.
Scleral lenses are another effective option, particularly for more advanced ectasia. These larger, gas-permeable lenses vault over the cornea, resting on the sclera. They create a fluid-filled reservoir that neutralizes corneal irregularities and provides a smooth refractive surface.
To prevent the condition from worsening, corneal collagen cross-linking (CXL) strengthens the collagen fibers within the cornea. This treatment involves applying riboflavin eye drops to the cornea, followed by exposure to ultraviolet A light. This creates new bonds between the collagen fibers, stiffening the cornea and often stabilizing ectasia progression.
For some individuals, intracorneal ring segments (Intacs) can be implanted into the cornea to help flatten its shape and improve vision. For severe ectasia where vision cannot be corrected, a corneal transplant (keratoplasty) may be necessary. This involves replacing the diseased cornea with healthy donor tissue. Deep anterior lamellar keratoplasty (DALK) is a common approach that preserves some of the patient’s own corneal layers.