Irregular Astigmatism: Causes and Risk Factors

Irregular astigmatism can be frustrating as you cannot see well at any distance without correction.

With normal astigmatism, the light entering the eye hits two different points instead of being refracted at just one. This is caused by the irregular shape of the eye or lens (the clear part inside the eye that directs rays to the light-sensitive retina at the back of the eye).

The problem is usually that the eye isn’t round and even, like a volleyball, but rather elongated, like a soccer ball, with more curvature in one area than another.

However, with irregular astigmatism, the surface of the eye can be uneven in many different ways, rather than just one. This can result in multiple different focus points, resulting in blurry vision.

This article examines common causes of irregular astigmatism and the role of genetics and lifestyle factors in the condition.

Common Causes

Irregular astigmatism can be caused by:

• Trauma at the surface, e.g. B. by an injury with a stick or branch
• Degenerative eye diseases such as keratoconusin which the cornea (the clear dome at the front of the eye) may develop a cone shape on the surface or anterior basement membrane dystrophy, in which the cornea loses firmness and becomes uneven
• Corneal surgery such as laser-assisted in situ keratomileusis (LASIK) with a complication such as a decentered ablation of the cornea (the clear surface reshaped by the excimer laser) or a flap problem

genetics

Certain diseases known to cause irregular astigmatism, like the following, have a genetic component. Such conditions can make the cornea prone to irregular astigmatism.

keratoconus

In keratoconus, the cornea thins and bulges forward, becoming cone-shaped. It causes refractive problems like myopia (where distance vision is blurry) and also irregular astigmatism. This is the result of both environmental factors, such as eye rubbing, and genetics.

Up to 23% of people with keratoconus have a family history. It appears that genes predispose some to keratoconus, usually when combined with environmental or other factors. Some genes that seem to play a role in keratoconus are:

• VSX1 gene: This gene is also associated with corneal dystrophy, in which one or more layers of the cornea are altered.
• SOD1 gene: This gene is linked to reactive oxygen species (produced by cellular metabolism) that can cause cell death.
• ZNF469 gene: This gene is linked to fragile corneal syndrome, a disease in which the cornea becomes thinner.
• TGFI Gene: This gene is linked to cell and collagen interactions.

Anterior basement membrane dystrophy

In anterior basement membrane dystrophy, the outer layer of the cornea does not develop properly and may erode. The epithelial basement membrane itself becomes thickened and very irregular, blurring your vision. This can be an inherited condition associated with the transforming growth factor-beta-induced gene (TGFBI).

Lifestyle Risk Factors

While the risk factors for irregular astigmatism are sometimes beyond your control, in others they can affect your lifestyle. For example, you can avoid having a refractive procedure like LASIK, where the development of an irregular astigmatism can be a complication.

Also, be sure to wear safety goggles when engaging in any activity (especially outdoors) that may cause eye injury. Environmental factors can affect people who are predisposed to keratoconus and those who are not.

Here are some possible factors to avoid:

• rub eyes: About half of people with keratoconus rub their eyes. This can last up to 180 seconds, as opposed to the typical five-second rub in people without the condition. It is believed that a small trauma to the epithelium from rubbing can contribute to an increase in inflammation and other activity in the area.
• sun exposure: People in hot, sunny places are more likely to develop keratoconus than those in shadier areas. This may be because reactive oxygen species can be caused by exposure to ultraviolet light.
• Nicotine use: Smoking cigarettes can in some cases increase the risk of keratoconus.

summary

An irregular astigmatism can cause your vision to be blurry at all distances. Blur occurs because the cornea (which focuses light onto the back of the eye) cannot bring focus to a single point. With irregular astigmatism, where the corneal surface is uneven, there may be several different focal points.

Irregular astigmatism can be caused by accidental trauma, a degenerative eye disease, or a complication of eye surgery such as LASIK. Genetics may play a role in the development of conditions such as keratoconus and anterior basement membrane dystrophy, which can lead to the development of irregular astigmatism.

Lifestyle factors such as eye rubbing, sun exposure, and smoking can also play a role in the development of some disorders associated with irregular astigmatism.

A word from Verywell

While avoiding irregular astigmatism is preferable and can be achieved in some cases, in others it is not. Still, paying attention to possible causes can help you minimize your difficulties with this condition.