Ideally, the surface of the eye should be curved like a sphere. This ensures light is focused onto a point on the retina and allows the brain to process images in focus, at any distance, from near to far.
Astigmatism is a condition where one or both eyes are not spherical like a soccer ball, but are shaped more like a rugby ball. The irregular shape does not allow light entering the eye to focus at a single point at the retina. Instead, the light is focused at multiple points, behind and/or in front of the retina, causing a blurred image to be sent to the brain.
Unlike myopia (near-sightedness) or hyperopia (long-sightedness), astigmatism causes blurred vision at all distances.
In actual fact, many people are born with a very mild form of astigmatism, but the effect on vision is negligible.
What causes astigmatism?
Astigmatism isn’t a disease and it isn’t contagious. Most people who have astigmatism are born with it although it isn’t known why this is the case. However, there is some evidence to suggest infants are more likely to be born with the condition if one or both parents have astigmatism.
Premature babies also have a higher percentage of astigmatism than full-term babies.
Astigmatism can also be caused by eye trauma as a result of an accident. There is also a degenerative condition called keratoconus, which causes the cornea to become thinner resulting in the development of high levels of astigmatism.
There are two common types of astigmatism:
- Corneal astigmatism: The cornea (the clear layer of tissue at the front of the eye) is oval in shape, rather than round and spherical. When this is the case, light rays focus on two different planes, with a blurred circle of vision forming on the retina. This results in a blurred image being sent to the brain resulting in images that are out of focus, both close up and far away.
- Lenticular astigmatism: This is when the lens of the eye, as opposed to the cornea, isn’t spherical in shape. In fact, most people with lenticular astigmatism tend to have a cornea that is regular in shape.
How is astigmatism diagnosed?
An optometrist will be able to perform the necessary tests, which may include the following:
- Assessment of corneal curvature using a device known as a keratometer.
- Computerised corneal mapping (also called topography), which looks at the shape of the corneal surface. This is performed with a keratoscope fitted with a video camera and is important in determining if Keratokonu is the cause of the astigmatism.
- A retinoscopy may be also used. It directs a beam of light into the eye to assess how effectively the eye can focus light.
- A device known as a phoropter may also be used and involves placing a series of corrective lenses in front of the eye. It is used to measure the exact level of visual correction required. The optometrist will exchange the lenses until the patient can clearly read the standard eye chart.
These tests assess the patient’s degree of refractive error and can accurately gauge the correct prescription for either glasses or contact lenses.
The most common treatment option is the prescription of glasses or contact lenses. This can be for astigmatism alone, or for a combination of astigmatism and short or long-sightedness.
An increasingly popular option for treatment of astigmatism is laser eye surgery. For many years now, there have been laser vision corrective procedures called LASIK and ASLA (also known as PRK).
LASIK is the most advanced and common form of laser eye surgery performed and is considered a safe and successful procedure. In fact, 99% of all people who have had LASIK are legally able to drive without glasses the day after surgery.
If a patient has irregular or thin corneas, then ASLA (PRK) may be recommended. The procedure is slightly different, but the end result is similarly effective.
Astigmatism is usually apparent from an early age, but children won’t necessarily know that it’s not normal to have blurred vision so might not complain. The effect on vision may be negligible in mild cases. However, all children should have regular eye tests to allow early detection and treatment of vision problems and avoid any negative impact on learning ability at school. There are a number of effective treatment options for astigmatism. Speak to your eye care professional for further information.
Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an apropriately qualified health practitioner.