Astigmatism

About astigmatism

If you have astigmatism, the way that your eye bends and focuses light rays is uneven. This is known as a refractive error. Refractive errors cause blurred vision and are the most common reason for seeing an optometrist (a registered health professional who examines eyes, tests sight and dispenses glasses and contact lenses). If you have astigmatism you may also have other refractive visual problems, such as short-sightedness (myopia) or long-sightedness (hyperopia).

When you look at an object, light rays pass into your eye through your cornea and lens, towards the retina at the back of your eye. If your eyes are completely regular in shape, the cornea is round and bends the light rays evenly onto a small area of your retina so that you can see the object clearly.

With astigmatism, the curve on your cornea is oval shape. This means that when light enters your eye from certain directions, it's not bent in the correct way to focus sharply on the retina. This creates a blur rather than a clearly focused image and the object that you're looking at will seem distorted or stretched slightly.

Symptoms of astigmatism

Most people have a form of astigmatism, though it's usually mild and doesn't need treatment. However, some people have more severe astigmatism which causes symptoms. These may include:

  • blurred or distorted vision – this may happen when looking at objects close-up and far away
  • eye strains
  • headaches

Causes of astigmatism

Astigmatism is usually caused by an abnormal oval curvature of your cornea. However, sometimes, astigmatism can be caused by an unequal bending of light by the lens inside your eye.

Some other possible causes of astigmatism are listed below.

  • Stitches put into your eye after surgery can cause your cornea to wrinkle, resulting in astigmatism. This usually gets better once your wound has healed and your stitches have been removed.
  • Surgery to your eye may cause scarring on your cornea. This changes the way light enters your eye and focuses on the retina.
  • A chalazion is a lump caused by a blocked gland on the inside of your eyelid. It can put pressure on your cornea forcing it to change shape, which causes astigmatism. This can get better if the chalazion is treated.
  • Keratoconus. This is a condition where the structure of your cornea changes from its normal shape to a cone shape.
  • An injury to your eye may cause damage to your cornea, changing its shape.

Diagnosis of astigmatism

Astigmatism is usually diagnosed during a routine eye examination, carried out by an optometrist. He or she may use one or more of the following tests to find out if you have astigmatism.

  • A visual acuity test. This involves reading letters on a distance chart.
  • Keratometry. This measures the curve of your cornea.
  • Refraction. A series of lenses are placed in front of your eyes and your optometrist will measure how well they focus.
  • Corneal topography. This is occasionally used to give more detail about the shape of your cornea. It scans your eye and creates a three-dimensional image.

These tests will help your optometrist to choose the best treatment for you, and the correct prescription for contact lenses or glasses.

It's important to have regular eye tests. Your optometrist can give you advice about when to be tested. A regular eye test can help to diagnose any visual problems and health conditions like high blood pressure and diabetes.

Treatment of astigmatism

Glasses and contact lenses

Wearing glasses or contact lenses can correct astigmatism – your optometrist will discuss both options with you. Your glasses are likely to have a special lens prescription to adjust for your astigmatism.

You can wear rigid gas-permeable contact lenses or soft contact lenses to treat astigmatism.

Rigid lenses work because they hold their shape and correct your cornea. They may last for up to a year before they need replacing and you will need to remove and clean them daily.

Soft contact lenses for astigmatism, often called toric lenses, are made to fit the shape of your cornea. One half of a toric lens is shaped with a steeper angle to correct your astigmatism. You will need to replace these either daily, or every two or four weeks. Soft contact lenses also need to be removed and cleaned after each period of wear.

See our frequently asked questions for more information.

Orthokeratology

Orthokeratology uses specially designed rigid gas-permeable contact lenses to reshape your cornea and correct your astigmatism. You wear the lenses at night and remove them during the day. When you wake up in the morning and remove the lenses, your cornea has been re-shaped giving you perfect vision. This means you don't need to wear glasses or contact lenses during the day. However, your cornea is very elastic and will always return to its natural shape, so you will need to wear the lenses regularly. This usually means wearing the contact lenses every night.

This treatment is only available if you have mild astigmatism. Talk to your optometrist if you're interested in orthokeratology.

Surgery

There are a number of different types of surgery that can treat astigmatism. Most of the procedures involve reshaping your cornea to allow light to focus correctly on the retina. Some of the main types of surgery are listed below.

  • Laser refractive surgery. Your surgeon will use a laser to even out the curve of your cornea, to make it round rather than oval. For more information see our frequently asked questions.
  • Radial keratotomy. Your surgeon will make several small cuts in your cornea to flatten it.
  • Corneal transplantation. Your surgeon replaces your cornea with a healthy one from a donor.
  • Toric intraocular lens implant. If you're having cataract surgery, it may be possible to replace the natural lens of your eye with an artificial one that will focus the light in a way that corrects your astigmatism (a toric lens).

Talk to your optometrist to find out more about the different types of surgery available, or ask for a private referral to an ophthalmologist.

Is it possible to be long- or short-sighted as well as having astigmatism?

Answer

Yes. Astigmatism is common if you're also short-sighted (myopia) or long-sighted (hyperopia).

Explanation

With normal vision, when you look at something, light rays pass into your eye through your cornea, then through the lens towards your retina at the back of your eye. In a healthy eye, the lens and cornea focus the light rays on a small area of the retina so that you can see the object clearly.

With short-sightedness, your eyeball may be too long or the optical power of your eye too strong. This means that the light entering your eye is focused in front of, rather than on, your retina. If you're short-sighted, it means that you can't see objects in the distance very clearly.

If you're long-sighted, your eyeball may be too short and your cornea may not be curved enough. This causes light rays entering your eye to focus behind your retina. This means that you may not be able to see objects that are close to you very clearly.

With astigmatism, the cornea is curved unevenly, causing the light rays to focus either behind your retina (hyperopic astigmatism) or in front of your retina (myopic astigmatism).

If you have long-sightedness or short-sightedness and have astigmatism, your optometrist will suggest treatment to correct both problems.

Is it safe to wear contact lenses if I have astigmatism?

Answer

Yes, it's usually safe to wear contact lenses if you have astigmatism.

Explanation

Many contact lenses are available for people with astigmatism to correct their vision. Rigid (hard or gas-permeable lenses) or soft contact lenses can be used to correct astigmatism. Rigid lenses hold their shape and correct the shape of your cornea. Soft, toric contact lenses for astigmatism are made to fit the shape of your cornea. One half of a toric lens is shaped with a steeper angle to correct your astigmatism. You will need to replace these either daily, every two or every four weeks and clean them after every period of wear.

Most people wear contact lenses during the day. However, there are some special rigid gas-permeable contact lenses used to treat astigmatism that you wear during the night to re-shape your cornea. When you take these lenses out, it will temporarily correct your astigmatism. This is called orthokeratology.

This treatment is only available if you have a mild astigmatism. Talk to your optometrist if you're interested in orthokeratology.

It isn’t common to have problems with contact lenses. However, wearing contact lenses can sometimes cause mild discomfort because of a dirty, dusty or damaged contact lens.

You're more likely to develop an eye infection if you wear soft lenses or wear lenses overnight, compared with wearing lenses during the day. It's important that you care for your lenses and follow the instructions given by your optometrist or doctor. Eye infections can quickly become serious if they aren't treated. If your eye becomes red and painful, you should take out your contact lenses and get medical help straight away.

What types of laser eye surgery can be used to correct astigmatism?

Answer

Several types of laser eye surgery can be used to treat astigmatism; these include LASIK, LASEK and PRK.

Explanation

Laser eye surgery can be used to treat astigmatism. If you’re short-sighted or long-sighted, this can also be corrected at the same time. There are three main types of laser surgery that can be used to treat astigmatism:

  • LASIK (laser-assisted in situ keratomileusis)
  • LASEK (laser epithelial keratomileusis)
  • PRK (excimer laser photorefractive keratectomy)

All of the above techniques use a computer-controlled laser to even out the curve of your cornea, changing it from an oval shape to a round shape. This allows light rays entering your eye to correctly focus on the retina.

It’s often recommended that your vision should have remained unchanged for the past 12 months before you can have laser eye surgery.

Surgery is usually done under local anaesthesia. This completely blocks feeling from your eye and you will stay awake during the operation.

In LASIK surgery, your surgeon will use a laser to make an ultra-thin flap in your cornea. He or she will then 'open' the flap (like the cover of a book) so that the laser can be used to shape the cornea underneath. Your surgeon will use the laser to remove precisely the right amount of cornea to re-shape it and then put the flap back in place.

With LASEK, your surgeon will use alcohol to loosen the surface layer of the cornea which is lifted as a flap. He or she will then use a laser to re-shape your cornea and then put the flap back.

PRK is the oldest technique and is less commonly used than other types of laser surgery. It’s usually used if you can’t have LASIK surgery, for example, if you have scars on your cornea. Your surgeon will use a laser to re-shape your cornea without having to cut it.

Laser surgery isn't suitable for everyone. If you have a medical condition, such as diabetes or rheumatoid arthritis, your surgeon may suggest other types of treatment.

There are many benefits to having laser eye surgery. However, there are also possible side-effects and complications. Before deciding on treatment it's important to discuss these with your ophthalmologist (a doctor specialising in eye health, including eye surgery).