Astigmatism is a common eye condition defined by an imperfection in the curvature of the eye’s focusing surfaces, such as the cornea or the lens. Normally, these surfaces are spherical, but with astigmatism, they are curved unevenly. This causes light to refract irregularly, preventing it from focusing on a single point on the retina. The result is blurred or distorted vision at any distance. A worsening of vision can be a natural, gradual process or the sign of an underlying structural change.
Natural Changes Related to Aging
The most frequent reason for a change in astigmatism is the natural process of aging within the eye. Over time, the crystalline lens gradually hardens and loses flexibility, a process known as presbyopia. This change alters how light passes through the eye, often changing an existing astigmatism measurement.
The lens also begins to cloud as a cataract forms, which inherently changes the eye’s refractive power. As the cataract matures, the lens thickens, causing a shift in the overall refractive error that can significantly worsen the measured astigmatism. Minor changes to the cornea also occur with age due to shifts in eyelid tension and internal eye pressure.
Many people experience a slow shift in the astigmatism axis, moving from a pattern called “with-the-rule” to “against-the-rule” as the cornea gradually flattens along the vertical meridian. This progression necessitates changes to your prescription to maintain clear vision. These age-related changes demonstrate that a worsening prescription is frequently a sign of normal ocular maturation.
Structural Diseases Causing Progression
A significant, and sometimes rapid, worsening of astigmatism can be caused by underlying diseases that physically alter the structure of the cornea. Keratoconus is a progressive condition where the cornea thins and bulges outward, taking on a cone-like shape. This deformation causes a severe form of irregular astigmatism that often cannot be fully corrected with standard eyeglasses.
This structural deformation is a concern when astigmatism worsens noticeably, particularly in adolescents and young adults. Frequent changes in glasses prescription are a sign that the corneal curvature is unstable due to this progression. Corneal scarring from injury, infection (like herpes keratitis), or complications from past eye surgery can also create permanent, uneven alterations to the corneal surface.
The resulting scar tissue drastically changes the surface curvature, leading to a fixed, high degree of astigmatism. Less commonly, other thinning disorders, such as Pellucid Marginal Degeneration, can mimic keratoconus by causing structural changes in the lower periphery of the cornea. In these cases, the worsening astigmatism is a direct result of a pathological change in the eye’s shape.
External and Lifestyle Contributors
Certain habits and temporary conditions can contribute to a perceived or actual worsening of astigmatism. Chronic and vigorous eye rubbing is a significant mechanical stressor that can physically deform the cornea over time. This repeated trauma weakens the collagen fibers that maintain the cornea’s dome shape, leading to a permanent change in curvature and is strongly linked to the progression of keratoconus.
Severe dry eye disease can cause vision to fluctuate, making astigmatism symptoms feel worse even if the underlying eye shape is unchanged. Dryness creates an unstable tear film on the surface of the eye, which temporarily disrupts the smooth surface light must pass through.
Ill-fitting or old contact lenses can irritate the cornea, causing temporary warpage or exacerbating dryness, which leads to unstable vision. Furthermore, certain systemic conditions, such as poorly controlled blood sugar levels in diabetes, can also cause temporary fluctuations in the lens shape and overall refractive error. Addressing these external factors can often stabilize vision and reduce the perceived severity of astigmatism.