Astigmatism is a common refractive error that occurs when the eye’s primary light-focusing structures, the cornea or the lens, are imperfectly curved. Instead of a smooth, spherical shape, the affected structure is shaped more like a football, causing light to bend unevenly as it enters the eye. This condition can definitively develop later in life, as changes due to aging or medical factors frequently lead to the development or significant progression of astigmatism in adulthood.
Mechanisms of Age-Related Astigmatism
The most common way astigmatism develops gradually later in life is through the slow, natural changes that occur in the structure of the eye. Over decades, the eye’s tissues lose some of their elasticity and rigidity, directly impacting the curvature of the cornea. This physiological process is the primary driver of astigmatism that emerges independent of acute disease or injury.
This age-related change is often characterized by a shift in the astigmatism axis, moving from “with-the-rule” (WTR) to “against-the-rule” (ATR) astigmatism. WTR astigmatism, common in youth, means the steepest curvature is along the vertical meridian. With age, the cornea tends to flatten vertically and steepen horizontally, resulting in ATR astigmatism.
This axial shift is believed to be caused by long-term alterations in the tension exerted on the cornea. The constant pressure from the upper and lower eyelids over a lifetime can physically change the shape of the corneal surface. Studies suggest that this shift towards ATR astigmatism occurs at a measurable rate, sometimes progressing by approximately 0.45 diopters every ten years between the ages of 36 and 68.
Changes within the eye’s crystalline lens also contribute to this phenomenon, leading to lenticular astigmatism. As the lens hardens and becomes less flexible, a process associated with presbyopia, its internal structure can distort. This hardening and shifting of the lens alter the way light is refracted, modifying the existing corneal astigmatism.
Medical Conditions and Procedures That Induce Astigmatism
Specific medical events and conditions common in later life can acutely cause or significantly worsen astigmatism. Beyond the slow, natural aging processes, one frequent cause is the development of cataracts, the clouding of the eye’s natural lens. As a cataract forms, the lens swells and changes shape, inducing a refractive error that can manifest as new or increased lenticular astigmatism.
Astigmatism can also be an acquired result of necessary eye procedures, known as post-surgical astigmatism. Following cataract surgery, incisions made in the cornea can alter its curvature until the wound is fully healed. Surgeons often use special toric intraocular lenses during cataract surgery to address pre-existing astigmatism and prevent new astigmatism from developing.
Conditions that affect the corneal tissue can induce irregular astigmatism, characterized by an uneven curvature across the surface. Keratoconus, where the cornea thins and bulges into a cone shape, typically starts earlier but its progression becomes more significant in adulthood. Irregular astigmatism is also a potential outcome following corneal transplant surgery or scarring from an eye injury.
Chronic ocular surface issues can temporarily or permanently affect corneal shape. Eyelid problems, such as a large chalazion or severe dry eye, can exert localized pressure on the cornea. This external pressure can deform the corneal surface, leading to an induced astigmatism that may resolve once the underlying condition is treated.
Recognizing Symptoms and Treatment Approaches
The symptoms of late-onset astigmatism often manifest as a gradual decline in visual clarity at all distances. Vision is blurry or distorted, making it difficult to focus on fine details. This blurring can be accompanied by ghosting, where a faint secondary image appears slightly offset from the primary image.
Nighttime driving often becomes challenging because astigmatism causes light sources to appear stretched, or surrounded by glare and halos. To compensate for this distorted vision, individuals frequently experience eyestrain, fatigue, and persistent headaches as their eyes work harder to achieve a clear focus.
Diagnosis is straightforward and performed during a routine comprehensive eye examination using specialized instruments. An eye care professional uses a phoropter to precisely measure the refractive error and a keratometer or corneal topographer to map the curvature of the cornea. These measurements determine the axis and magnitude of the astigmatism.
The condition is managed effectively with several treatment options. For most people, the simplest solution involves corrective lenses, either eyeglasses or contact lenses. Toric contact lenses are specifically designed with different optical powers in different meridians to correct the uneven curvature.
In some cases, surgical correction may be an option for those who want to reduce their dependence on corrective lenses. Procedures like LASIK or photorefractive keratectomy (PRK) use lasers to reshape the cornea. These surgeries are generally reserved for stable astigmatism, though they are often integrated into cataract surgery to provide simultaneous vision and astigmatism correction.