Myopia

Page last reviewed: 13/07/2011

Short-sightedness (myopia) is a problem of vision that causes distant objects to appear blurred, while close objects can still be seen clearly.

This is because light rays are being focused in front of the retina (the inside of the back of the eye), rather than directly on the retina.

Myopia is caused by the eye being too long from front to back, or the cornea (the front of the eye) being too steeply curved. The result is a mismatch between the length of the eye and its focusing power.

The degree of myopia is determined by the focusing power of the lens, which is measured in dioptres (D):

  • mild-degreemyopia is between 0.5D and 3.0D
  • medium-degreemyopia is between 3.0D and 6.0D
  • high-degreemyopia is 6.0D and over

How common is it?

In the UK at least 5 million people are short-sighted, and about 200,000 of them have high-degree myopia.

How is it treated?

Myopia can usually be corrected with glasses (spectacles) or contact lenses. Surgery to correct myopia is available, although most people pay for this privately (see Myopia - treatment for more information).

Page last reviewed: 13/07/2011

The main symptom of myopia is distant objects appearing blurred, while near objects can still be seen clearly. Other symptoms can include headache and tired eyes.

When does short-sightedness occur?

Myopia usually appears around puberty, but can appear at any age from early childhood up to 25 years of age.

Usually, the degree of myopia increases with age because the eyeball grows as the child grows. In most cases, myopia stops intensifying when the person stops growing.

In older people, the onset of myopia can be the earliest indication that a cataract (cloudy lens) is starting to form.

Some children who develop myopia may not realise at first that their vision has been affected. They may be able to read books and do 'close work' well, but may find it difficult to see distant objects, such as the blackboard at school. Often, they think this is 'normal' and do not tell anyone.

Children may have their vision checked at school. If not, parents should book their children for a sight test with an optometrist (optician). See Myopia - diagnosis.

Severe myopia

Myopia that starts in early childhood often gets worse in adult life and may become very severe. Known as high-degree myopia, it can create problems later in life because of associated changes at the back of the eye. 

There is a slight risk of reduced vision, which can be severe in some cases because the increased size of the eyeball 'stretches' the retina, thereby damaging it.

Page last reviewed: 13/07/2011

There is a tendency for myopia to run in families, although it is believed that a number of factors combine to cause myopia. 

A person's genetic make-up, and the environment they grow up in, are considered to be linked to the development of myopia.

Blurred vision can also be a symptom of other health problems (see box, right).

Genetic factor

Children have an approximately 30% chance of developing myopia if one of their parents has the condition, and a 55% chance if both have it.

Environmental factors

People who spend a lot of time reading, working at a computer or doing other close-vision work may develop temporary myopia (where vision returns after resting the eyes). Also, they may be more likely to develop permanent myopia.

Some people develop 'night myopia' - blurred distance vision that only occurs at night. This is because blue light makes the eyes artificially short-sighted, and a small degree of myopia becomes more significant at night.

Genes
Genes contain information that you inherit from your parents, such as eye or hair colour. They are carried by chromosomes.

Conditions that cause blurred vision

  • Blurred vision in people with diabetes can be a sign of diabetic retinopathy (damage to the tiny blood vessels that nourish the retina). For more information on this, go to the A-Z topic on Diabetic retinopathy.
  • Myopia may be a sign of a developing cataract (a cloudy patch in the lens) – see the A-Z topic on Age-related cataracts.

Page last reviewed: 13/07/2011

An optician will usually diagnose myopia after a sight test. The optician will use a letter or symbol chart to record the level of vision and see if lenses can correct it to normal.

Children may have their vision checked at school. If not, parents should book their children for a sight test with an optician.

Children should have their sight tested at least every two years.

Free sight tests

Undert the Treatment benefit Scheme run by the Department of Social Protection, insured workers and retired people who have the required number of PRSI contributions are entitled to optical services. Medical card holders are legally entitled to ophthalmic services from the HSE but,in practice the availability of these services may vary from area to area.

Page last reviewed: 13/07/2011

Glasses and contact lenses

Myopia can usually be corrected with glasses (spectacles) or contact lenses. These cancel out the increased curvature of your cornea or the increased length of your eye, so that distant objects no longer appear blurred.

Laser treatment

Laser surgery works by altering the shape of the cornea so that the eye focuses correctly. It is generally suitable for treating low degrees of myopia.

Most people pay for laser treatment privately.

Current evidence suggests that laser surgery for the correction of myopia is safe and effective for use in patients who have been appropriately selected.

However, as with any surgery, there are possible complications you need to be aware of (see Myopia - complications) The two available procedures are described below.

Laser in-situ keratomileusis (LASIK)

A small flap is made in the cornea, and a tiny piece of tissue is removed with a laser. It is usually performed as an outpatient procedure and takes about 15 minutes for each eye. Vision may be hazy or blurry for a few days after surgery.

Photorefractive keratectomy (PRK) 

A laser is used to remove tissue from the cornea and reshape it. The treatment may be painful for 48 hours afterwards. It can only be used to treat less severe myopia.

Lens implant surgery

In lens implant surgery a contact lens is implanted in your eye to correct severe short-sightedness (high-degree myopia). It is sometimes referred to as intra-ocular lens insertion or corneal implant insertion.

There are two main ways of performing lens implant surgery:

  • Inserting a phakic implant - a contact lens is permanently inserted into your eye without removing your natural lens ('phakic' means the eye contains its natural lens)
  • Replacing your natural lens with an artificial one, sometimes known as refractive lens exchange. 

Inserting a phakic lens implant

This procedure is generally used for people aged 25-45 for whom laser surgery is not suitable, or for people who have difficulty wearing glasses, for example because of a disability or professional requirement.

It is the preferred technique for younger (aged under 45) patients because their natural, unaided reading vision is preserved.

The procedure is carried out using a local anaesthetic, and you can go home the same day. Your pupil is dilated using eye drops and a phakic lens implant is inserted into your eye via a small cut in your cornea (front of the eye).

Depending on its design, the phakic lens is anchored to your iris (coloured part of the eye), placed in the angle between your cornea and iris, or positioned to float over the surface of your natural lens.

The second eye is usually treated about a week after the first.

The National Institute for Health and Clinical Excellence (NICE) published guidelines on lens implants (PDF, 58kb) in February 2009. It concluded that there is good evidence of short-term safety and efficacy, but there is an increased risk of cataract, corneal damage or retinal damage. There is no long-term data about this.

Therefore it is important to talk to your doctor about this procedure and understand the risks involved.

Replacing your natural lens with an artificial one 

This procedure is essentially the same as cataract surgery. Your natural lens is replaced with an artificial lens that corrects your short sightedness.

Refractive lens exchange is usually a day case procedure performed under general or local anaesthetic.

The operation is not painful, and you will be able to see clearly within two days of the surgery. The second eye is usually treated about seven days after the first.

 

Page last reviewed: 13/07/2011

Complications of myopia

If you have severe short-sightedness (high-degree myopia) you are more likely to develop eye disorders in later life, such as retinal detachment, glaucoma and cataracts.

Complications of surgery

Complications of surgery to correct myopia can include:

  • clouding of the cornea (although this tends to improve quickly)
  • glare around bright lights
  • over-correction (leading to long-sightedness) or under-correction
  • infection of the cornea
  • increased pressure in the eye (glaucoma)
  • puncture of the cornea or eyeball
  • retinal detachment (when the retinal lining separates from the back wall of the eye), which requires urgent surgical treatment to prevent permanent loss of vision

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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