Astigmatism is a common refractive error. It occurs when the front surface of the eye, the cornea, or the lens inside the eye, has an imperfect curvature. Instead of being perfectly round, the affected part of the eye is shaped more like an egg or a football. This irregular shape causes light to bend unevenly, leading to blurred or distorted vision at various distances.
Understanding Genetic Predisposition
Astigmatism frequently presents with a significant hereditary component, tending to run in families. Individuals with parents or close relatives who have this eye condition often face an increased likelihood of developing it. This genetic predisposition arises because the eye’s intricate shape and structure, particularly the curvature of the cornea and lens, are influenced by inherited genetic factors. Twin studies consistently support a substantial genetic contribution, with heritability estimates for corneal astigmatism often ranging around 60% to 71%.
A genetic predisposition means an individual is more susceptible to developing astigmatism, but it does not imply a simple, direct inheritance pattern. It functions as a risk factor, meaning these genes increase susceptibility without certainty of developing the condition. Even with a family history, the condition may not manifest, or its severity can vary, highlighting the complex interplay between inherited traits and other influences. The genetic influence is not typically tied to a single gene but involves a more complex interaction of multiple genes.
How Astigmatism is Inherited
Astigmatism is considered a polygenic trait, meaning its development is influenced by multiple genes rather than a single one. This complex genetic architecture makes predicting its inheritance pattern more intricate than simple dominant or recessive models. While specific genes linked to astigmatism are still under investigation, research has identified variations in genes such as PDGFRA, CLDN7, ACP2, and TNFAIP8L3 as potentially associated with corneal astigmatism. The cumulative effect of these genetic contributions shapes the eye’s curvature and overall structure.
The familial tendency of astigmatism is well-documented: if one or both parents have the condition, their children face a significantly higher likelihood of developing it. Recent research underscores a clear dose-dependent relationship between parental and child astigmatism. For example, a study revealed that children with both parents having astigmatism of 1.0 Diopter (D) or more had increased odds of developing refractive astigmatism (1.62 times) and corneal astigmatism (1.94 times). This risk amplifies with greater parental severity; if both parents exhibited astigmatism of 2.0 D or more, the odds for their children rose to 3.10 for refractive astigmatism and 4.31 for corneal astigmatism. This suggests that more pronounced parental astigmatism leads to a higher risk for their offspring.
What is inherited is primarily the genetic predisposition for astigmatism, not necessarily the condition itself with guaranteed severity or onset. The intricate interplay of these multiple genes, combined with environmental factors, ultimately determines if and how astigmatism manifests. Therefore, while a strong family history signals an increased risk, it does not mean every child will inevitably develop the condition, and its expression can vary widely even within the same family.
Non-Genetic Causes of Astigmatism
While genetics play a significant role, astigmatism is not exclusively hereditary; other factors can cause or contribute to its development. Eye injuries are a notable non-genetic cause, as trauma to the eye can lead to scarring or irregular healing of the cornea, altering its shape. This can result from incidents including foreign objects, chemical exposure, or blunt force.
Certain eye diseases can also induce or exacerbate astigmatism. Keratoconus, for instance, is a progressive condition where the cornea thins and bulges outward into a cone shape. This irregular corneal surface leads to significant visual distortion and often severe irregular astigmatism. The natural aging process can also alter the curvature of the eye’s lens, and conditions like cataracts can contribute to or induce lenticular astigmatism as the lens changes shape.
Eye surgery, particularly procedures involving the cornea or lens, such as cataract surgery, can sometimes result in or worsen astigmatism. This is known as surgically induced astigmatism and can occur due to factors like incision size and placement, healing response, or intraocular lens positioning. Although astigmatism can be present from birth, these non-genetic influences demonstrate it can also develop or change in severity throughout a person’s life, independent of inherited predispositions.