Keratoconus and myopia are both conditions that affect how light is focused on the retina, leading to blurred vision. Although they share some visual symptoms, they are distinct in their causes and progression. However, there is a recognized connection between the two, as keratoconus often produces or worsens myopia due to changes in the shape of the cornea.
Understanding Myopia
Myopia, also known as nearsightedness, occurs when the eye focuses light in front of the retina instead of directly on it. This typically happens because the eyeball is too long or the cornea has too much curvature. Individuals with myopia see nearby objects clearly but have difficulty focusing on distant objects.
The degree of myopia can vary from mild to severe. Mild myopia can often be corrected with glasses or contact lenses, while higher levels may require more advanced treatments such as orthokeratology or refractive surgery. Myopia is extremely common and usually develops during childhood or adolescence, progressing gradually until early adulthood.
Understanding Keratoconus
Keratoconus is a progressive corneal disorder characterized by thinning and outward bulging of the cornea into a cone-like shape. This distortion prevents light from focusing correctly on the retina, leading to irregular astigmatism and blurred or distorted vision. Unlike simple refractive errors, keratoconus involves structural changes in the corneal tissue.
The exact cause of keratoconus is not fully understood, but it is believed to involve a combination of genetic, biochemical, and environmental factors. Chronic eye rubbing, allergies, and oxidative stress are known to contribute to its progression. The condition usually begins in adolescence or early adulthood and may worsen over time if not properly managed.
How Keratoconus and Myopia Interact
Keratoconus often leads to an increase in myopia as the cornea becomes steeper and thinner. The steepening of the cornea increases its refractive power, which causes light to focus in front of the retina, creating the same type of blur seen in myopia. As keratoconus progresses, this induced myopia typically becomes more severe and irregular.
In early keratoconus, patients are sometimes misdiagnosed as having simple myopia or astigmatism because vision can initially be corrected with standard glasses or contact lenses. Over time, as the corneal shape becomes more distorted, conventional corrective lenses no longer provide adequate vision. This is often the point at which keratoconus is accurately diagnosed through corneal topography or tomography, which measure corneal curvature and thickness in detail.
Shared Risk Factors
Although keratoconus and myopia are distinct conditions, they share several risk factors. Both are more common in younger individuals and can be influenced by genetics. A family history of either condition increases the likelihood of development. Eye rubbing, which can mechanically stress and thin the cornea, is a known risk factor for keratoconus and can also worsen myopia by altering corneal curvature.
Diagnostic Considerations
When evaluating patients with progressive or high myopia, clinicians often screen for keratoconus to rule out structural abnormalities of the cornea. Advanced diagnostic tools such as corneal topography, pachymetry, and tomography are used to detect early changes in corneal shape or thickness. Identifying keratoconus early is important because management strategies differ significantly from those for simple myopia.
Patients with rapidly changing prescriptions, especially for astigmatism, should be evaluated for possible keratoconus. Similarly, those who experience increasing difficulty obtaining clear vision with glasses or soft contact lenses may need specialized testing to confirm or exclude the condition.
Management of Coexisting Keratoconus and Myopia
When keratoconus and myopia coexist, treatment focuses on both improving vision and preventing further corneal distortion. In mild cases, glasses or soft contact lenses may correct vision effectively. As keratoconus progresses, rigid gas-permeable or scleral contact lenses are often needed to create a smoother optical surface and improve visual clarity.
To slow or stop progression, corneal collagen cross-linking is used to strengthen the corneal tissue. This procedure increases collagen bonding within the cornea, stabilizing its structure and reducing the risk of further thinning or steepening. Cross-linking does not reverse myopia but can prevent additional refractive changes caused by corneal deformation.
In advanced cases, when scarring or severe distortion occurs, corneal transplantation may be necessary. After transplantation, residual myopia and astigmatism are often corrected with glasses, contact lenses, or refractive procedures.