Causes and Risk Factors of Irregular Astigmatism

Having irregular astigmatism can be frustrating since you can't see well at any distance without correction.

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

The problem usually is that instead of the eye being round and even, like a volleyball, it's somewhat stretched out, like a football, with more of a curve in one area than another.

But with irregular astigmatism, the eye's surface can be uneven in many different ways instead of just one. This can cause several different points of focus, leading to blurred vision.

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

Common Causes

Irregular astigmatism can be caused by the following:

• Trauma to the surface, such as from an injury with a stick or branch
• Degenerative eye diseases such as keratoconus, in which the cornea (the clear dome at the front of the eye) can develop a cone shape on the surface, or anterior basement membrane dystrophy, in which the cornea loses strength 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 that is reshaped by the excimer laser) or a flap issue
  

Genetics

Certain diseases known to cause irregular astigmatism, such as the following, have a genetic component. Such conditions can leave the cornea vulnerable to irregular astigmatism.

Keratoconus

With keratoconus, the cornea thins and bulges forward, steepening into a cone shape. It causes refractive issues such as nearsightedness (in which distant vision is blurry) and also irregular astigmatism. This is the result of both environmental factors such as eye rubbing, as well as genetics.

As many as 23% of people with keratoconus have a family history of it. It seems that genes may predispose some to keratoconus, usually when this is combined with environmental or other factors. Some genes that appear to play a role in keratoconus include:

• VSX1 gene: This gene is also associated with corneal dystrophy, which involves changes to one or more of the layers of the cornea.
  
• SOD1 gene: This gene is associated with reactive oxygen species (generated by cell metabolism) that may cause cell death.
• ZNF469 gene: This gene is linked to brittle cornea syndrome, a disease involving the thinning of the cornea.
• TGFI gene: This gene is associated with cell and collagen interactions.

Anterior Basement Membrane Dystrophy

With anterior basement membrane dystrophy, the outside layer of the cornea does not develop properly and may erode. The epithelial basement membrane itself becomes thickened and very irregular, causing your vision to become blurred. This can be a hereditary condition that is associated with the transforming growth factor beta-induced gene (TGFBI).

Lifestyle Risk Factors

While risk factors for irregular astigmatism may be out of your control in some instances, in others, how you lead your life may have an impact. You can, for example, avoid undergoing a refractive procedure such as LASIK, in which the development of irregular astigmatism can be a complication.

Also, if you are engaging in activities (particularly outside) that can cause eye injury, be sure to wear protective eye gear. Environmental factors can affect people predisposed to keratoconus and those who are not.

Here are some potential factors to try to avoid:

• Eye rubbing: About half of people with keratoconus rub their eyes. This may go on for as long as 180 seconds, as opposed to a typical five seconds of rubbing in people without this condition. There's some thinking that small trauma to the epithelium from rubbing may contribute to a rise in inflammation and other activity in the area.
• Sun exposure: Those in hot, sunny locales are more likely to develop keratoconus than those in shadier areas. This may be the result of the fact that reactive oxygen species can be caused by exposure to ultraviolet light.
• Use of nicotine: Smoking cigarettes can heighten the risk of developing keratoconus in some cases.

Summary

Having irregular astigmatism can leave you with blurry vision at all distances. Blurriness occurs because the cornea (which focuses light onto the back of the eye) cannot get the focus down to a single point. With irregular astigmatism, where the corneal surface is uneven, there may be several different points of focus.

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

Also, lifestyle factors such as eye rubbing, exposure to sunlight, and smoking can play a role in developing some conditions related to irregular astigmatism.

A Word From Verywell

While avoiding irregular astigmatism is preferable and can be accomplished in some cases, in others this will not be possible. Still, being alert to potential causes may help you minimize difficulties with this condition.