What is astigmatism?
Astigmatism means the lens in the eye ( cornea) isn't perfectly curved so that vision is distorted or blurred.
This is called a refractive error and means the eye shape is more like a rugby ball than round. Only part of anything you are looking at is in focus and other things will be blurred.
Astigmatism can range from mild to severe. It can also be regular or irregular. Regular astigmatism is easier to treat than the irregular kind, where the curve can go in different directions. Astigmatism can affect one or both eyes.
Untreated astigmatism can lead to eye strain, fatigue and headaches. However, it can be corrected by glasses, contact lenses or laser eye surgery.
What causes astigmatism?
A person may inherit the tendency to have astigmatism, and babies can be born with it.
It is hard to diagnose vision problems in young children and so it may not be detected until a child is older and can explain their blurred vision to an optician or health professional during routine eye tests.
Astigmatism can also result from eye injuries, eye operations and other health conditions.
What are the symptoms of astigmatism?
As well as general blurred vision, additional astigmatism symptoms include:
- Difficulty reading small print
- Squinting some things that are close or far away
- Light sensitivity.
If your eyesight is not as clear as it could be, or if it seems to be causing problems like headaches, see an optician.
Tests used to diagnose it include:
Visual acuity test. This is the classic test where you are 6 metres away and are asked to read rows of letters that get smaller and smaller.
Refraction. A special lens machine called a phoropter is used to hold different corrective lenses in front of the eye. Lenses are changed in the phoropter until the letter chart is clearer. The lenses used in the machine form the basis of a glasses or contact lens prescription. The light reflex from the eye is also checked for refractive errors using a handheld device called a retinoscope.
Keratometry. This device measures the curvature of your central cornea lens to check if it is symmetrical, and if not, what is needed to correct the curvature.
Corneal topography. A computer is used to measure and form a 3-D image of the surface of the lens called a corneal map.
How is astigmatism treated?
Mild astigmatism may not need to be corrected, but it may be monitored to see if it gets worse over time.
If the astigmatism is moderate to high, special 'toric' corrective lenses will usually be recommended to improve vision, as well as dealing with any shortsightedness or longsightedness at the same time.
Eye surgery is another option to change the shape of the lens using a laser. The optician or ophthalmologist will be able to advise about whether this is an option, the risks and the costs – as the NHS is unlikely to fund the treatment. Refractive surgery is not usually recommended if a person has retinal problems, corneal scars or eye disease.
Astigmatism cannot be prevented.