Astigmatism

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at May 5, 2016
StartDiseasesAstigmatism

Astigmatism is an eye condition that is extremely common. The most minor cases require no treatment and show no symptoms. An astigmatism of a higher degree may cause a number of symptoms related to vision problems, but there are many treatments available.

Contents

Definition & Facts

This very common eye condition occurs when the cornea or lens of an eye is irregularly shaped without the smooth natural curvature of the eye. Portions of the cornea or lens could be flatter or steeper in different directions. This causes light to be improperly focused and vision to become blurred.

This condition can be present at birth, and commonly occurs with nearsightedness or farsightedness. This optical problem is not contagious and occurs just as often in adults as it does in children. Types of astigmatism include corneal astigmatism, which is defined by the irregular shape of the cornea, and lenticular astigmatism in which the lens of the eye has an abnormal shape.

Symptoms & Complaints

As with many optical conditions, the main complaint from patients is blurry or distorted vision. The severity of visual distortion depends on the degree to which the curvature of the cornea or lens is irregular. Blurry vision is normally seen at all distances and can be more defined in one direction, whether horizontally, vertically or diagonally.

Headaches and eye strain are also common symptoms and can be caused by squinting or straining to increase visual focus. Sufferers may also notice difficulty driving at night or during bad weather conditions. The eyes can become more sensitive to light and an increase in blinking may occur. If these symptoms are present, proper testing from an ophthalmologist will determine the presence of an astigmatism rather than other optical conditions.

Causes

Astigmatism is caused by the irregularly shaped cornea or lens. This causes the light entering the eye to be improperly focused which creates the symptoms characteristic of astigmatism. This condition can be present at birth or develop later in life due to an injury to the eye, certain diseases, or as a side effect from surgery. However, the cause of the naturally occurring astigmatism is unknown. Some studies have found that astigmatism can be inherited from one's parents. It is also more apparent in babies who are born prematurely or with low body weight.

This abnormal curvature of the cornea cannot be caused by excessive reading, sitting too close to the television or squinting in low light situations. It is possible that lenticular astigmatism in which the lens is irregularly shaped, could be caused by diabetes. High sugar levels can be a factor in the lens changing shape. Proper diagnosis and treatment of these types of lenticular astigmatism can reverse the effect and the lens can possibly return to its normal shape. 

Diagnosis & Tests

A routine eye examination can detect an astigmatism using techniques commonly used for verification of nearsightedness or farsightedness. A retinoscopy is a test optometrists use to estimate the severity of an astigmatism. This simple test is done by shining a light into the eye while placing a series of lenses between the light and the eye.

After this preliminary test, a manual refraction is done. This is done by placing a phoropter in front of the patient's eyes and switching the lenses back and forth for easy comparison. The test's result is used to determine the optimal eyeglass or contact prescription to produce clear vision.

Keratometry can also be used to determine astigmatism of the cornea. A special device called a keratometer measures the steepest and flattest areas of the cornea and is essential to properly fit contact lenses. Corneal topography is another test used to gather information on corneal astigmatism. This device takes thousands of measurements of the cornea while the patient simply looks at an object. These measurements are then used by a computer to create a detailed picture of the affected cornea.

Treatment & Therapy

After the presence of astigmatism is confirmed, various treatments are used to help the eye evenly distribute light to produce a clear picture. Very minor cases require no treatment other than regular eye exams to monitor optical changes. One option for some cases is the use of prescription eyeglasses or specially developed contact lenses. The specific prescription is different for every patient as it counteracts the specific astigmatism shape. Depending on the degree of astigmatism, soft lenses or gas-permeable rigid contact lenses can be used. Usually the rigid contact lenses are prescribed for those with a high degree of astigmatism.

Another treatment option is laser eye surgery. This is done by surgically changing the shape of the cornea. A thin flap of cornea is cut, lifted and pushed back, exposing the deep corneal layers for treatment. After sculpting and reshaping is completed by a surgeon, the outer flap is intricately placed back into its original position. Antibiotics are commonly prescribed to prevent infection.

There are a few downsides to corrective laser eye surgery. Additional surgeries could be required due to an over-correction or under-correction of the cornea's shape. Glares could impair vision in low light situations. The eye could be subject to increased dryness. Patients over 40 years of age may still be required to wear glasses under certain circumstances, such as reading or using a computer. Laser eye surgery is not an option for all patients including:

Prevention & Prophylaxis

Unfortunately, astigmatism is often an optical phenomenon with no known cause. As a result, there is no proven way to prevent these irregularities of the eye. A possible way to prevent astigmatism due to eye injury is to practice good and hygienic optical care:

  • Do not rub the eye
  • Wear protective eye wear when working with hazardous machinery
  • Avoid blowing debris such as sand, sawdust and dirt
  • Properly care for and clean prescribed contact lenses