Keratoconus is a progressive eye condition where the normally round, dome-shaped cornea thins and gradually bulges outward into a cone-like shape. This alteration in corneal shape causes light rays entering the eye to scatter, leading to distorted and blurred vision. While there is no known cure that completely reverses the condition, various medical devices play a central role in managing keratoconus. These devices are designed to improve visual acuity and, in some cases, halt the progression of the corneal thinning.
Corrective Lenses for Vision Improvement
For individuals with early or mild keratoconus, standard eyeglasses or custom soft contact lenses may provide sufficient vision correction. Eyeglasses correct for mild astigmatism and nearsightedness that often accompany initial stages. Custom soft contact lenses offer a wider range of parameters, allowing for a better fit on slightly irregular corneas compared to conventional soft lenses. These options are suitable when the corneal irregularity is not yet pronounced.
As keratoconus progresses and the corneal shape becomes more irregular, specialized contact lenses are required to achieve clear vision. Rigid Gas Permeable (RGP) lenses are a common choice due to their firm structure. These lenses create a smooth, regular refractive surface over the irregular cornea, with a layer of tears filling the space between the lens and the eye. This tear layer neutralizes the corneal irregularities, allowing light to focus effectively onto the retina.
Hybrid contact lenses combine features of both RGP and soft lenses, with a rigid gas permeable center surrounded by a soft skirt. The RGP center provides clear vision, while the soft skirt enhances comfort and stability. These lenses can be a good option for patients who experience discomfort with traditional RGPs but still require significant vision correction due to corneal irregularity. The soft periphery helps with centering and overall lens awareness.
Scleral lenses are another advanced option, covering a larger area of the eye and resting on the white part (sclera) rather than directly on the cornea. These large-diameter lenses vault over the irregular corneal surface, creating a fluid-filled reservoir between the lens and the cornea. This fluid layer smooths out corneal irregularities, providing a clear optical surface for optimal vision. Scleral lenses are beneficial for advanced keratoconus cases or for patients with sensitive eyes, offering comfort and stable vision.
Surgically Implanted Devices
When corrective contact lenses no longer provide adequate vision, surgically implanted devices can reshape the cornea and improve vision. Corneal ring segments, such as Intacs, are small, transparent, arc-shaped pieces of plastic implanted into the middle layer of the cornea. Made of polymethyl methacrylate (PMMA), these segments are inserted through tiny incisions. The procedure aims to flatten the central cone of the cornea.
The placement of these segments alters the curvature of the cornea, making its surface more regular. This reshaping can reduce astigmatism and myopia caused by keratoconus. Patients who undergo this procedure often experience improved uncorrected vision or achieve better vision with less complex corrective lenses. This intervention is for patients with progressing keratoconus who can no longer achieve functional vision with non-surgical methods but do not yet meet criteria for a corneal transplant.
Devices for Corneal Cross-Linking
Another category of medical devices focuses on halting keratoconus progression rather than improving existing vision. Corneal cross-linking (CXL) procedures strengthen corneal tissue using specific medical devices. The process involves applying riboflavin eye drops, a photosensitizing agent, to the cornea. After riboflavin saturates the cornea, a device delivers a controlled dose of ultraviolet A (UVA) light.
The interaction between riboflavin and UVA light initiates a photochemical reaction within corneal collagen fibers. This reaction forms new chemical bonds, or “cross-links,” between collagen fibrils. These cross-links increase corneal stiffness and rigidity, making it more resistant to further thinning and bulging. The goal of this treatment is to stabilize the cornea, prevent worsening keratoconus, preserve current vision, and potentially delay the need for more invasive interventions like corneal transplantation.
Diagnostic and Monitoring Technology
Accurate diagnosis and ongoing monitoring of keratoconus rely on imaging technology. Corneal topography is a non-invasive diagnostic device that maps the outer surface of the cornea. It uses a Placido disc, projecting concentric rings of light onto the corneal surface, with a camera capturing the pattern. Distortions in these rings indicate corneal shape irregularities, analyzed to create detailed, color-coded maps. These maps highlight steepening and thinning characteristic of keratoconus.
Corneal tomography builds upon topography by providing a comprehensive three-dimensional analysis of the cornea, including its front and back surfaces and thickness profile. Devices like the Pentacam use a rotating Scheimpflug camera to capture multiple cross-sectional images. This technology detects subtle changes in corneal shape and thickness not visible with topography alone. These detailed maps are fundamental for initial diagnosis, tracking progression, and precisely guiding the custom-fitting of specialized contact lenses.