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Astigmatism





Astigmatism

Causes of astigmatism

The vision problems caused by astigmatism are a result of defects within the eye. In most cases, these defects are present from birth.

To understand the causes of astigmatism, it is useful to understand how the eye works.

How the eye works

The eye is made up of three components:

  • the optical system (cornea and lens)
    located at the front of the eye; they act like a camera lens, helping focus the light coming into the eye to form an image on the retina
  • the retina – located at the back of the eye; it is a light-sensitive layer of tissue that senses light and colour and converts them into electrical signals
  • the optic nerve – the ‘cable’ that transmits the electrical signals from the retina to the brain, where they are interpreted and understood

Astigmatism usually occurs as a result of problems with the cornea or lens.

The cornea and lens

The cornea is a transparent layer of tissue that covers the front of the eye. It helps to protect the eye from damage. The cornea and lens are also responsible for focusing incoming light onto the retina to create a clear image.

To work properly, the cornea needs to be perfectly curved, like a football. In cases of astigmatism, the shape of the cornea is irregular, like a rugby ball.

When light hits an irregularly curved cornea, the light is not focused correctly onto the retina. Instead, the incorrect focus blurs the image, resulting in blurred vision. Astigmatism caused by problems with the cornea is known as corneal astigmatism.

The same problem can also sometimes be caused by an irregular shaped lens that bends light unevenly in the eye. This is known as lenticular astigmatism.

It is not known why some people are born with astigmatism – there may be a hereditary element.

Other causes

Other possible causes of astigmatism include:

  • injuries to the cornea, such as an infection that scars the cornea 
  • changes to the cornea caused by eye surgery
  • keratoconus and keratoglobus – eye conditions that cause the cornea to bulge, get thinner and change shape
  • some conditions that affect the eyelids
  • other diseases that affect the cornea or lens

Published Date
2013-01-14 11:48:32Z
Last Review Date
2012-10-15 00:00:00Z
Next Review Date
2014-10-15 00:00:00Z
Classification
Astigmatism,Eye






Astigmatism

Diagnosing astigmatism

Astigmatism is usually diagnosed after a routine eye test.

Regular eye tests

Most people who have astigmatism are born with the condition, so it is important your children have regular eye tests.

If your child is born with astigmatism, they may not realise there is anything wrong with their vision. If their vision is not regularly tested, conditions like astigmatism could be undiagnosed for many years, which can cause a lazy eye. In addition, if a child has uncorrected astigmatism, they may have difficulty reading and concentrating at school.

When to get tested

Your baby will have their eyes checked at birth to ensure they are healthy.

Any later concerns regarding your child’s eyes can be raised with your GP or health visitor.

If your child has suspected vision problems, they may be referred to an orthoptist. An orthoptist specialises in problems relating to the development of vision in children. They usually work in local health clinics or hospital eye clinics.

Most orthoptic departments in NHS hospitals test children’s vision at three to four years of age and report any problems to an ophthalmologist. An ophthalmologist is a medical doctor who specialises in eye conditions and their treatment. They mainly work in hospitals and hospital eye departments.

You may also see an optometrist. Optometrists examine eyes, test sight and prescribe glasses and contact lenses. They are trained to recognise eye conditions and sight defects.

If your child’s vision has been checked and is normal, they should continue to have regular eye checks about once every year.

Adults should have an eye test at least every two years, unless advised otherwise by their optometrist.

Testing for astigmatism

A number of tests can be used to diagnose astigmatism. The two most common tests are described below.

Visual acuity test

A visual acuity test can be used to assess your or your child’s ability to focus on objects at different distances. It usually involves reading letters on a chart called a Snellen chart. The letters become progressively smaller on each line of the chart.

Keratometer

A device called a keratometer can measure the degree of corneal astigmatism. It measures how light is being focused by the cornea (the transparent layer of tissue at the front of the eye), and it can detect irregularities in the curve of the cornea.

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Published Date
2013-01-14 11:48:51Z
Last Review Date
2012-10-15 00:00:00Z
Next Review Date
2014-10-15 00:00:00Z
Classification
Astigmatism,Eye tests






Astigmatism

Introduction

Astigmatism is a common and usually minor condition of the eye that causes blurred or distorted vision.

It occurs when the cornea or lens is not a perfectly curved shape. Most people who wear glasses have astigmatism.

If left untreated, astigmatism can also cause:

  • headaches
  • eye strain and fatigue (tiredness) – particularly after doing tasks that involve focusing on something for a long period of time, such as reading or using a computer

Why does it happen?

Astigmatism is usually the result of an irregular-shaped cornea or lens.

The cornea is the transparent layer of tissue at the front of the eye. The cornea should be shaped like a football, but in cases of astigmatism it has an irregular curve, more like a rugby ball. This means that light rays entering the eye are not focused properly, creating a blurred image.

In most cases, astigmatism is present at birth. However, it sometimes develops after an injury to the eye or as a complication of an eye operation.

Read more about the causes of astigmatism.

How it is diagnosed

Astigmatism is usually diagnosed after a routine eye test, which often involves testing your ability to focus your eyes.

It is important both for you and and your children to have regular eye tests, as astigmatism can sometimes go undiagnosed for years and it can affect your or your child’s ability to read and concentrate.

Read more about diagnosing astigmatism.

Treating

In many cases, the symptoms of astigmatism are so mild that no treatment is needed to correct your vision. In cases where your vision is significantly affected by astigmatism, glasses or contact lenses can be used to correct it.

Laser treatment can be used to permanently correct astigmatism in adults. However, it is unlikely you will be able to receive laser treatment through the NHS.

Read more about treating astigmatism.

Published Date
2013-01-14 11:48:13Z
Last Review Date
2012-10-15 00:00:00Z
Next Review Date
2014-10-15 00:00:00Z
Classification
Astigmatism,Eye conditions

































































Astigmatism 

Introduction 

In many cases, the symptoms of astigmatism are so mild that no treatment is required 

Refractive errors

Astigmatism belongs to a group of related eye conditions known as refractive errors. Other common refractive errors include:

If you have astigmatism, it is likely you also have one of these conditions. 

Astigmatism is a common and usually minor condition of the eye that causes blurred or distorted vision.

It occurs when the cornea or lens is not a perfectly curved shape. Most people who wear glasses have astigmatism.

If left untreated, astigmatism can also cause:

  • headaches
  • eye strain and fatigue (tiredness) – particularly after doing tasks that involve focusing on something for a long period of time, such as reading or using a computer

Why does it happen?

Astigmatism is usually the result of an irregular-shaped cornea or lens.

The cornea is the transparent layer of tissue at the front of the eye. The cornea should be shaped like a football, but in cases of astigmatism it has an irregular curve, more like a rugby ball. This means that light rays entering the eye are not focused properly, creating a blurred image.

In most cases, astigmatism is present at birth. However, it sometimes develops after an injury to the eye or as a complication of an eye operation.

Read more about the causes of astigmatism.

How it is diagnosed

Astigmatism is usually diagnosed after a routine eye test, which often involves testing your ability to focus your eyes.

It is important both for you and and your children to have regular eye tests, as astigmatism can sometimes go undiagnosed for years and it can affect your or your child’s ability to read and concentrate.

Read more about diagnosing astigmatism.

Treating

In many cases, the symptoms of astigmatism are so mild that no treatment is needed to correct your vision. In cases where your vision is significantly affected by astigmatism, glasses or contact lenses can be used to correct it.

Laser treatment can be used to permanently correct astigmatism in adults. However, it is unlikely you will be able to receive laser treatment through the NHS.

Read more about treating astigmatism.

Page last reviewed: 16/10/2012

Next review due: 16/10/2014

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Astigmatism

Treating astigmatism

In many cases, the symptoms of astigmatism are so mild that treatment to correct your vision is not required.

If treatment is necessary, it usually involves wearing glasses or contact lenses.

Corrective lenses

Corrective lenses work by compensating for the irregular curve of the cornea (transparent layer of tissue at the front of the eye), so that incoming light passing through the corrective lens is properly focused onto the retina. The retina is the light-sensitive layer of tissue at the back of the eye.

Usually, glasses and contact lenses are equally as effective in treating astigmatism. Therefore, the type of corrective lenses you decide to use will depend on your personal preference and the advice of your optometrist. Your optometrist is the healthcare professional who examines your eyes, tests your sight, and prescribes and provides any glasses or contact lenses.

There is no medical reason why children cannot wear contact lenses, although the opinion of your optometrist will be important in deciding if they are suitable. Most children over 12 years old will be able to wear them. However, it is important your child is able to use their lenses correctly. They must be able to follow any instructions related to their lenses, such as how long to keep them in, and when to clean them.

Contact lenses

If you choose to wear contact lenses, it is important to keep good lens hygiene to prevent eye infections. Read more about contact lens safety.

There are three different types of contact lenses:

  • rigid contact lenses
  • gas permeable contact lenses
  • soft contact lenses

These are described in more detail below.

Rigid contact lenses

Rigid contact lenses are made from a combination of plastic and glass. The disadvantage of rigid contact lenses is that they prevent oxygen from getting into the eye. A lack of oxygen can make your eye produce new blood vessels, which may obscure your vision.

These are an old-fashioned type of lens, and may not be commonly used for astigmatism.

Gas permeable contact lenses

Gas permeable contact lenses use a type of plastic that allows oxygen to pass through the lens and into your eye. These materials are known as gas permeable or oxygen permeable.

Soft contact lenses

Soft contact lenses are made from a mixture of water and polymer, which is known as a hydrogel.

The water in the lens allows oxygen to enter your eye. In some soft lenses, the water evaporates quickly, so you can only wear them for a short time before they need to be replaced. However, newer materials, such as silicone gel, are oxygen permeable, so you can wear them for longer.

There are several varieties of soft contact lenses, such as:

  • lenses you wear for one day, then throw away after taking them out in the evening
  • lenses you wear every day for one month, taking the lenses out every evening and putting them in again in the morning 
  • lenses that you wear continuously for one month, then replace

While soft contacts can be helpful, they are not usually as effective at treating astigmatism as rigid or gas permeable contacts.

Laser eye surgery

Laser surgery involves using lasers (narrow beams of light) to remould the tissue of the cornea to change its curve.

Laser surgery to correct astigmatism is not usually available free on the NHS because it is not considered an essential medical treatment, and other effective treatments are available, such as glasses and contact lenses.

However, the National Institute of Health and Clinical Excellence (NICE) announced in 2011 that corrective laser surgery could be a treatment option on the NHS to improve vision after previous eye surgery.

Laser surgery is usually carried out on an outpatient basis. This means you will not have to stay in hospital overnight. Instead, you will have one or more appointments at a specialist eye clinic. The treatment usually takes 20 to 30 minutes.

There are three different types of laser surgery:

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

These are described below.

Photorefractive keratectomy (PRK)

During photorefractive keratectomy (PRK), the outer layer of cells of the corneal surface is removed. A laser is used to remove tissue to change the shape of the cornea. The surface of the cornea is then left to heal. PRK is quite an old procedure now and is not as common as the other two types of laser surgery.

Laser epithelial keratomileusis (LASEK)

Laser epithelial keratomileusis (LASEK) is a similar procedure to PRK, but it involves using alcohol to remove the layer of cells on the surface of the cornea. A laser is then used to change the shape of the cornea. After treatment has finished, the surface layer of cells will grow back naturally after a few days.

Laser in situ keratomileusis (LASIK)

During laser in situ keratomileusis (LASIK), a flap of tissue is created either mechanically, with a machine called a microkeratom, or with a specialised kind of laser called a femtosecond laser. The flap is lifted up to expose the underlying corneal tissue, which is then treated with laser reshaping.

The flap is then repositioned on the eye. LASIK is often the preferred laser treatment option because it causes little pain and your vision starts to recover within a few hours. Full recovery of vision can take a little longer, however.

LASEK and PRK are more painful procedures than LASIK. It can take up to a week for your vision to recover. Full vision recovery typically takes around three to four weeks after LASEK or PRK.

LASIK treatment can only be carried out if your cornea is thick enough. If your cornea is too thin, the risk of complications and side effects, such as a corneal ectasia (see below), is too high. LASEK and PRK may be possible if your cornea is not thick enough for LASIK surgery.

When laser eye surgery can be used

People under 21 years of age should not have corrective laser surgery of any type. This is because their vision may still be changing and it is unwise to alter structures of the eyes at this stage.

Your vision can also change when you are over 21. Before carrying out laser treatment, your eye care clinic should check your glasses or contact lens prescription to confirm your vision has been stable for at least two years.

Laser surgery may also not be suitable for you if:

  • you have diabetes, which can cause abnormalities in the eyes that can be made worse by laser surgery to the cornea
  • you are pregnant or breastfeeding – your body will contain hormones that cause slight fluctuations within the eye, making precise surgery too difficult
  • you have a condition that affects your immune system (the body’s natural defence system) – conditions such as HIV and AIDS or rheumatoid arthritis may affect your ability to recover after surgery
  • you have other problems with your eyes, such as glaucoma (an eye condition that damages the optic nerve) or cataracts (where the lens of the eye becomes cloudy); these conditions will need to be treated before laser surgery to avoid the risk of any damage

Risks of laser eye surgery

As with all surgical procedures, laser surgery carries some risks. Possible complications of laser surgery include:

  • your vision may get worse if the amount of tissue taken from your cornea is more or less than intended; this is known as a correction error
  • the surface of your cornea can begin to grow into the other layers of the cornea; this is known as epithelial ingrowth and it can cause problems with your vision that may need to be corrected with more surgery 
  • your cornea becomes too thin and your vision is reduced or lost; this is called ectasia
  • your cornea becomes infected; this is called microbial keratitis

All of the above risks are very rare. For example, in 2006, NICE found that after laser surgery there was around a 1 in 100 chance of one of these complications occurring. 

Although information about the risks of LASEK and PRK is not as comprehensive as it is for LASIK, the risk factors are thought to be similar.

More recent research into laser eye surgery has also found the risks of complications to be low. Ask your surgeon to explain possible risks before your operation.

Read more about laser eye surgery.

Published Date
2013-01-14 11:49:09Z
Last Review Date
2012-10-15 00:00:00Z
Next Review Date
2014-10-15 00:00:00Z
Classification
Astigmatism,Diabetes,Eye,Eye specialists,Immune system,Laser eye surgery,Laser surgery,Spectacles