Keratoconus is a progressive condition where the cornea, the clear, dome-shaped front surface, thins and begins to bulge outward into a cone-like shape. This change disrupts the cornea’s ability to focus light, leading to distorted and blurred vision. The condition begins in a person’s late teens to early thirties and can advance over 10 years or more. While it affects both eyes, the severity and rate of progression can differ between them.
Initial Symptoms of Keratoconus
The onset of keratoconus is subtle, with symptoms that can be mistaken for common vision issues. Individuals may first notice a slight blurring of their vision or that straight lines appear bent or distorted. This can be accompanied by an increased sensitivity to bright lights and glare, which may create difficulties with driving at night.
Another sign of early keratoconus is the need for frequent changes in eyeglass or contact lens prescriptions. As the cornea’s curvature becomes more irregular, previous prescriptions are no longer effective. Some people may also experience monocular polyopia, seeing multiple “ghost” images or halos around a single object. These symptoms can fluctuate and may worsen in one eye more rapidly than the other.
Associated Risk Factors and Causes
The precise cause of keratoconus is under investigation, but it is believed to result from a combination of genetic and environmental influences. A family history is a known risk factor, as approximately one in ten individuals with keratoconus has a parent with the disease, suggesting a genetic predisposition.
There is a strong association between keratoconus and chronic eye rubbing. The mechanical stress from persistent rubbing can weaken the cornea’s structural integrity over time, particularly in predisposed individuals. This habit is often linked to conditions that cause itchy eyes, such as allergies and atopic eye disease.
The condition is also linked with systemic disorders that may weaken corneal tissue. These include:
- Ehlers-Danlos syndrome, which affects collagen production
- Down syndrome
- Osteogenesis imperfecta
- Retinitis pigmentosa
The Diagnostic Examination
The diagnostic process for keratoconus often begins during a routine eye exam. An eye doctor may investigate further if a patient reports rapidly worsening vision or if there are frequent changes in an eyeglass prescription, particularly those involving high or irregular astigmatism.
For a definitive diagnosis, specialized imaging tests are used. Corneal topography is a non-invasive procedure that creates a detailed, three-dimensional map of the cornea’s surface. This map highlights irregularities like steepening or bulging, allowing for detection of the cone-like shape even in its earliest stages. This mapping is used for both confirming the diagnosis and monitoring the condition’s progression.
An eye doctor will also perform a slit-lamp examination. This involves using a high-magnification microscope to get a detailed, cross-sectional view of the cornea that can reveal signs like thinning. Another diagnostic test is pachymetry, which is used to measure the thickness of the cornea. Identifying the thinnest point of the cornea helps confirm the diagnosis and assess its severity.
Managing Early-Stage Progression
The management of early-stage keratoconus focuses on improving vision and halting the disease’s progression. In the mildest cases, vision can be corrected with eyeglasses or standard soft contact lenses. As the cornea becomes more irregular, glasses may no longer provide adequate clarity, and specialty contact lenses are required.
Rigid gas-permeable (RGP) lenses are a common option, as they create a smooth refractive surface over the cornea for sharper vision. Other specialty lenses include:
- Custom soft toric lenses
- Hybrid lenses, which combine a hard center with a soft outer skirt
- Scleral lenses, which are larger lenses that vault over the entire cornea
To address the progression of the disease, a procedure called corneal cross-linking (CXL) is the standard of care. This minimally invasive treatment is designed to strengthen the corneal tissue to prevent it from bulging further. The procedure involves applying riboflavin (vitamin B2) eye drops to the cornea, which is then activated by a controlled application of ultraviolet (UV) light. This process creates new bonds, or cross-links, between the collagen fibers within the cornea, making it more stable. CXL is intended to stop the condition from worsening, not to reverse existing damage or eliminate the need for corrective lenses.