Keratoconus is a progressive eye condition affecting the cornea, the clear, dome-shaped front surface of the eye. The cornea’s role is to focus light as it enters the eye, allowing for clear vision. In keratoconus, the cornea thins and weakens over time. This causes it to bulge outward into a cone-like shape, which disrupts how light is focused on the retina, leading to distorted and blurry vision.
Symptoms and Progression
The initial signs of keratoconus often appear during the late teenage years or early twenties. Early symptoms commonly include mild blurring of vision, an increased sensitivity to bright lights and glare, and visual distortions, such as straight lines appearing bent. As the condition progresses, these symptoms become more pronounced and can interfere with daily activities like driving or reading.
The progression of keratoconus can continue for 10 to 20 years before it slows or stabilizes, often around age 40. During this active phase, individuals may experience frequent changes in their eyeglass prescription, increasing nearsightedness or astigmatism, and ghosting or double vision in a single eye. The condition affects both eyes, but the progression rate and severity can differ between them. In some cases, the cornea can swell suddenly, causing a rapid decrease in vision, a condition known as hydrops.
Causes and Risk Factors
The precise cause of keratoconus remains unknown but likely results from a combination of genetic and environmental influences. A family history of the condition is a significant risk factor, as about one in ten people with keratoconus has a parent with the disease. This genetic predisposition is thought to weaken the corneal structure.
Chronic and vigorous eye rubbing is strongly associated with the development and progression of keratoconus, as the pressure can weaken a predisposed cornea. The condition is also linked to certain systemic disorders, including allergic conditions like hay fever and asthma, and connective tissue diseases such as Ehlers-Danlos syndrome and Down syndrome.
The Diagnosis Process
An eye doctor can detect initial signs of keratoconus during a comprehensive eye exam. If keratoconus is suspected, specific diagnostic procedures are performed to confirm the diagnosis and assess the condition’s severity.
The most definitive tool for diagnosis is corneal topography, also known as corneal mapping. This imaging test creates a detailed, three-dimensional map of the cornea’s surface, revealing the characteristic cone-like bulge and any irregularities. Another procedure is a slit-lamp examination, where a microscope is used to view the cornea in high magnification to observe its shape and look for signs of thinning. A pachymetry test may also be used to measure the thickness of the cornea, which helps in tracking the progression of the thinning.
Treatment Approaches
Treatment for keratoconus is tailored to the individual and the stage of the condition, focusing on correcting vision and preventing further progression. In the earliest stages, mild astigmatism and nearsightedness can be managed with eyeglasses or standard soft contact lenses, which provide clearer vision for a time.
As the cornea becomes more irregular, eyeglasses and soft lenses may no longer provide adequate vision correction. Specialized contact lenses are then required to create a smooth refractive surface over the misshapen cornea. Rigid gas permeable (RGP) lenses are a common choice because their firm material vaults over the cone, neutralizing visual distortion. Other options include hybrid lenses, with a hard center and soft outer skirt for comfort, and scleral lenses, which rest on the white of the eye and vault over the cornea.
For patients whose condition is actively progressing, a procedure called corneal cross-linking (CXL) is recommended. CXL is the only treatment available that can slow or halt the advancement of keratoconus by strengthening the cornea’s structure. The procedure involves applying riboflavin (vitamin B2) eye drops to the cornea, which is then activated by ultraviolet light. This process creates new bonds between the collagen fibers within the cornea, making it stiffer and more stable.
In advanced cases where contact lenses are no longer effective or comfortable, surgical interventions may be considered. One option is the implantation of plastic inserts called Intacs, which are placed within the cornea to help flatten the cone and improve its shape. For patients with severe scarring or extreme thinning, a corneal transplant, or keratoplasty, may be necessary to restore vision.