Astigmatism is a common refractive error where the eye’s shape is irregular, causing light to bend unevenly as it enters the eye. This irregularity can occur in the cornea, the clear front surface of the eye, or the lens inside the eye. The result is blurred or distorted vision at all distances, as light cannot properly focus on the retina, the light-sensitive layer at the back of the eye. Instead of being perfectly round like a basketball, an eye with astigmatism is shaped more like a football or the back of a spoon.
How Astigmatism Develops and Evolves
Astigmatism can manifest at any point in life; some individuals are born with it, while others acquire it as their eyes grow and change. The prevalence of astigmatism in young children tends to decrease as their eyes develop, a process known as emmetropization. However, astigmatism does not remain stable throughout childhood, with some children losing it and others developing it.
Astigmatism can remain stable for many years, subtly progress, or change significantly. As individuals age, the prevalence of astigmatism generally increases, and the axis of astigmatism can shift. This progression may eventually require corrective lenses, even if they were not needed initially.
Factors Influencing Astigmatism Changes
Aging is a primary factor, as natural changes in the eye can alter the cornea’s shape and affect the flexibility of the lens. This can lead to increased astigmatism. Alterations in the position and tension of the eyelid, corneal stromal collagen, and extraocular muscles may also influence the shape of the cornea with age.
Certain eye conditions can induce or alter astigmatism. Keratoconus, a condition where the cornea progressively thins and bulges into a cone shape, can exacerbate astigmatism. Other conditions like pterygium, a growth on the white part of the eye, or chalazion, a cyst on the eyelid, can also cause irregular astigmatism. Complications from cataracts, which involve clouding of the eye’s lens, can lead to lenticular astigmatism.
Physical trauma to the eye can also change corneal shape, leading to new or worsened astigmatism. Injuries from foreign objects, chemical exposure, or blunt force can cause the cornea to heal irregularly, affecting how light refracts. Eye surgeries, such as cataract surgery or corneal transplants, are another factor that can induce or correct astigmatism due to alterations in the shape of the lens or cornea. Prior refractive surgeries like LASIK or PRK can sometimes lead to changes in astigmatism.
Managing Astigmatism and Its Changes
Regular eye exams are a very important step for monitoring astigmatism and detecting changes early. Consistent check-ups allow eye care professionals to track the condition’s progression and adjust treatment plans. This proactive approach helps ensure visual requirements are met and can prevent long-term vision problems, particularly in children where untreated astigmatism can lead to amblyopia, also known as “lazy eye”.
Eye care professionals use various instruments to detect and measure astigmatism. A phoropter allows the doctor to test different lens strengths, while a keratometer measures corneal curvature. Corneal topography provides a detailed map of the corneal surface, identifying irregularities. These diagnostic tools help determine the precise prescription needed for clear vision.
Corrective lenses are a primary treatment, with eyeglasses utilizing cylindrical lenses designed to compensate for the uneven shape of the eye. Toric contact lenses are specifically designed to provide stability and clarity for individuals with astigmatism. For those seeking a more permanent solution, refractive surgeries like LASIK (Laser-Assisted In Situ Keratomileusis) or PRK (Photorefractive Keratectomy) use lasers to reshape the cornea, improving how light focuses on the retina. In cases where cataracts are present, toric intraocular lens (IOL) implants can be used during cataract surgery to correct astigmatism. For specific conditions like keratoconus, specialized treatments such as corneal cross-linking may be employed to strengthen the cornea and prevent further bulging.