Short-sightedness

Short-sightedness is a very common eye condition that causes distant objects to appear blurred, while close objects can be seen clearly.

Information written and reviewed by Certified Doctors.

Contents

Introduction

Short-sightedness is a very common eye condition that causes distant objects to appear blurred, while close objects can be seen clearly. Myopia is the medical term for short-sightedness.

Cases of short-sightedness can range from mild, where treatment may not be required, to very severe, which can significantly affect vision.

The symptoms of short-sightedness often start around puberty and get gradually worse until the eye is fully grown. Therefore it's important to have regular eye examinations.

If you notice that distant objects seem to be fuzzy or your child is struggling to see things in the distance, such as the blackboard at school, you should arrange for a sight test with an optometrist (optician).

What causes short-sightedness?

Short-sightedness is a refractive eye condition. Refractive eye conditions are caused when problems with the structure of the eye affects how light rays enter your eye.

Most people are born slightly long-sighted (where close objects appear blurred) because their eyes haven't grown to their full length. The eye then grows to their normal length, which should lead to the resumption of normal vision.

Generally, short-sightedness happens when the eye continues to grow and becomes too long from front to back As a result, light rays don't reach the retina at the back of the eye. They only focus in front of it. This means that objects in the distance seem blurred.

Most cases of short-sightedness are caused by a combination of genetic and environmental factors that disrupt the normal growth of the eye.

Read more about the causes of short-sightedness.

Treating short-sightedness

There are three main treatment options for short-sightedness. They are:

  • using corrective lenses, such as glasses or contact lenses, to compensate for the defect in the cornea
  • using laser surgery – to correct the defect (laser surgery can't be used in children because their eyes are still developing); most people will have to pay to have private laser surgery
  • implanting an artificial lens into the eye to compensate for the longer eye length

Read more about treating short-sightedness.

Who is affected by short-sightedness?

Short-sightedness is a refractive eye condition. Refractive eye conditions are caused when problems with the structure of the eye affects how light rays enter your eye.

Most people are born slightly long-sighted (where close objects appear blurred) because their eyes haven't grown to their full length. The eye then grows to their normal length, which should lead to the resumption of normal vision.

Generally, short-sightedness happens when the eye continues to grow and becomes too long from front to back As a result, light rays don't reach the retina at the back of the eye – they only focus in front of it. This means that objects in the distance seem blurred.

Most cases of short-sightedness are caused by a combination of genetic and environmental factors that disrupt the normal growth of the eye.

Short-sightedness is thought to be slightly more common in females than in males.

Read more about diagnosing short-sightedness.

Symptoms

When does short-sightedness occur?

Short-sightedness usually occurs around puberty, but it can start at any age, including very young children. It's unusual to start after the age of 30, although older people may become short-sighted due to cataracts (see below).

Younger children may think that blurred vision is normal, so their symptoms may only be noticed once they start school and find it difficult to read the blackboard.

Short-sightedness usually becomes worse as a child gets older because as the child grows, the eye grows longer. Short-sightedness tends to stabilise when a person is fully grown, though it may progress until the mid- to late- 20s.

In older people, the onset of short-sightedness can be an early indication that a cataract is forming. Cataracts are changes in the transparent lens in the eye causing it to be less clear, resulting in blurred or cloudy vision. They're usually associated with ageing.

If you notice the symptoms of short-sightedness in you or your child, you should arrange a sight test with an optometrist (optician).

Degrees of short-sightedness

Healthcare professionals use a measurement called dioptres (D) to describe how short-sighted a person is. The higher the measurement, the longer the eye and/or the more highly curved their cornea is (the transparent front of the eye). Dioptres in short-sighted eyes are written as a negative measurement (-3D) in contrast to long-sighted eyes which are written as a positive measurement (+3D).

Three classifications are used for describing the severity of short-sightedness. They are outlined below.

Mild myopia

Mild-degree myopia is a measurement of between -0.5D and -3D. This is the most common type of short-sightedness. While you may manage without glasses or contact lenses, these may be recommended for certain activities, such as watching television or driving.

Moderate myopia

Moderate myopia is a measurement of between -3D and -6D. It's likely that people with this type of short-sightedness will have to wear glasses or lenses full-time.

High myopia

High myopia is a measurement of more than -6D. People with this type of short-sightedness can only see close objects clearly without glasses if they hold them very close to their eye.

Other eye conditions

Short-sightedness is associated with some serious eye conditions. Generally, the more short-sighted you are, the higher the risk of these problems.

Short-sighted people have an increased risk of developing glaucoma, an eye condition in which increased pressure can lead to loss of the peripheral vision (field of vision). It's a reason why people over the age of 40 should have regular eye tests as you may be unaware of having early glaucoma.

There's also an increased risk of developing retinal detachment. This is where the lining at the back of your eye (the retina) begins to peel away from the deeper layers of the eye, rather like wallpaper peeling off a wall. Without prompt treatment, retinal detachment will cause blindness in the affected eye.

Highly short-sighted people can experience damage to the central part of the retina (the macula). This is known as macular degeneration. It can cause permanent poor vision for reading and close work, but this usually develops in older age.

Causes

The structure of the eye

To understand how short-sightedness (myopia) can develop, it's useful to learn about the overall structure of the eye. The eye is made up of the:

  • cornea – the transparent outer layer of the eye
  • lens – a curved, transparent structure that sits behind the cornea
  • retina – a thin layer of light-sensitive tissue at the back of the eye
  • optic nerve – the nerve that transmits signals from the eye to the brain

Rays of light pass through the cornea and into the lens, both of which focus the rays onto the retina to create an image. The image is converted into an electric signal, which is transmitted to the brain via the optic nerve. This in effect allows the brain to see.

To produce a perfectly clear image, the cornea should be smooth and evenly curved, and the eye the right length. However, in many cases of short-sightedness, the eye has grown too long. In a few people, it may be that the cornea is more curved than normal.

This means that when you try to look at distant objects, the light is not focused directly onto your retina but a short distance in front of it.

This results in the image that's sent to your brain being blurred.

It's unclear what makes the cornea develop abnormally, or the eye to grow longer than normal. However, the genes that you inherit from your parents seem to be involved because short-sightedness runs in families.

Inheriting short sight

If one of your parents is short-sighted, you have around a 40% chance of developing the condition yourself. The risk increases to around 60% if both of your parents are short-sighted.

Close work

There appears to be some truth to the ‘old wives’ tale’ that too much reading in bad light is bad for your eyes.

There certainly seems to be some connection between children or young adults who spend a lot of time doing ‘close work’, such as reading, writing and computer work, and an increased risk of developing short-sightedness.

One study found that children who read for 30 minutes or more per day were 1½ times more likely to develop short-sightedness than children who didn’t.

However, as reading brings personal enjoyment and educational achievement, many people who enjoy it, or parents who encourage their children to read, are willing to accept some risk of short-sightedness.

More recent research has found that outdoor activity, such as playing sports, can often help to prevent short-sightedness becoming worse.

This protective effect could be connected with the much higher light levels outside than inside and/or the fact that the child doesn't have to focus on close objects.

Most experts would recommend an ‘everything in moderation’ approach. Children should be encouraged to read, but also encouraged to spend time each day away from computer games and reading, and doing some activity outdoors.

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

Diagnosis

Most cases of short-sightedness (myopia) are diagnosed by an optician during an eye test. Opticians are healthcare professionals who specialise in diagnosing common eye conditions, such as short-sightedness. They also prescribe corrective lenses.

During an eye test, your vision will be tested with and without your glasses or contact lenses (if you wear them). So remember to take them with you.

Your optician will usually assess your distance vision, your near vision (for close work, such as reading) and your intermediate vision (for using a computer). A simple 'visual acuity' test helps the optician to assess how good your vision is. You will be probably asked to read from a chart displaying letters that become smaller on each line.

If you have problems reading the letters at a distance that most people can read easily, you're likely to be diagnosed with short-sightedness.

Further testing

To be able to measure how severe your shortsightedness is, your optician will use a test called a retinoscopy, where a bright light is shone in your eye to see how the retina reacts.

You may also be asked to look at a chart through a series of different strength lenses, to see how they affect your vision. This will help the optician to determine what strength your prescription should be.

How often should I have an eye test?

Adults and children are usually advised to have an eye test at least every two years. However, in some circumstances, your optician may recommend that you have an eye test more frequently. For example, this may be the case if you:

  • have diabetes (a long-term condition that's caused by too much glucose in the blood)
  • are 40 years old or over and have a family history of glaucoma (a group of eye conditions that affect vision)
  • are 70 years old or over

Free eye tests

Please ask your doctor for details of any free eye tests that may be available to you.

Treatment

The most common treatment for short-sightedness (myopia) is to correct your eyesight using glasses or contact lenses. Laser surgery to correct short-sightedness is also becoming increasingly popular.

A relatively new technique that can be used if laser surgery is not possible, or is ineffective, is to implant artificial lenses in the eyes.

Each treatment option is discussed in more detail below.

Corrective lenses

Glasses

Short-sightedness can usually be corrected using glasses that are made specifically to your prescription.

Concave lenses are used to correct short-sightedness. Concave lenses are thicker at the edge than at the centre. The curvature of the lens, its thickness and weight will depend on how short-sighted you are. Wearing a lens that's made to your prescription will ensure that light rays fall onto your retina and you can focus accurately.

The lens of the eye becomes less flexible with age, which means that you may need to use two pairs of glasses, with one pair for ‘close vision’ activities, such as reading, and the other pair for ‘distance vision’ activities, such as watching television.

Alternatively, some people use bifocal lenses, which allow them to see objects clearly that are both close up and far away, or use “monovision” with one lens set for distance and the lens in the other eye set for close work.

Contact lenses

Contact lenses can also be used to correct vision in the same way as glasses. Many people prefer contact lenses to glasses because they're lightweight and almost invisible.

There are two types of contact lenses – rigid gas-permeable contact lenses and soft contact lenses. However, there are many different lens materials and designs.

Contact lenses can be worn on a daily basis and discarded each day (daily disposables), or they can be disinfected and re-used, or they can be worn for a longer period of time. However, eye specialists generally recommend that they're not worn overnight because of risks of infection.

Your optician will be able to advise you about the most suitable type of contact lenses for you.

If you choose to wear contact lenses, it's very important that you maintain good lens hygiene to prevent eye infections.

A technique called orthokeratology is occasionally used by some opticians. This involves wearing a hard contact lens overnight to flatten the curvature of the cornea so that you can see better without a lens or glasses during the day. It's not a “cure” for short-sight, as the cornea recovers to its normal shape, but can reduce reliance on lenses for low or moderate short-sighted people.

Laser surgery

Laser surgery involves using a laser to burn away small sections of your cornea(s) to correct their curvature so that the light is less tightly focused through your lens and on to your retina. There are three main types of laser surgery, which are briefly outlined below.

Photorefractive keratectomy (PRK)

Photorefractive keratectomy (PRK) involves a small amount of the surface of the cornea being removed before a laser is used to remove tissue and change the shape of the cornea. The amount of tissue removed is controlled by a computer and will depend on how poor your eyesight is. The surface of the cornea is then left to heal.

Laser epithelial keratomileusis (LASEK)

Laser epithelial keratomileusis (LASEK) is a similar procedure to PRK but involves using alcohol to loosen the surface of the cornea before it's lifted out of the way. As with PRK, a laser is then used to change the shape of the cornea. Once the treatment is finished, the surface of the cornea is replaced and is held in place by natural suction.

Laser in situ keratectomy (LASIK)

Laser in situ keratectomy (LASIK) is similar to LASEK, but only a small flap of the cornea is involved. A surgical instrument is used to cut a flap in the surface of the cornea, which is then folded back rather than removed. A laser is then used to change the shape of the cornea. When the laser work is finished, the flap is folded back down to its original position and held in place by natural suction.

The laser surgery operation

Laser surgery is usually carried out on an outpatient basis. This means that you won't have to stay overnight in hospital, but you'll have one or more appointments at a clinic. The treatment takes around 30 minutes to an hour.

LASEK or LASIK are usually the preferred methods because they causes almost no pain and your vision recovers within one to two days. However, you may experience some fluctuations in your vision after this. It can take up to a month for your vision to stabilise completely and for you to feel the full benefits of the operation.

Laser treatment can only be carried out if your cornea is thick enough. If your cornea is thin, the risk of complications and side effects occurring, such as loss of vision, is too great.

LASEK and PRK may be possible if your cornea is not thick enough for LASIK surgery. However, the recovery time tends to be longer using these techniques – for example, it can take up to six months for your vision to stabilise after having PRK surgery.

Results

The results of all three techniques are usually good. While it may not always be possible to completely cure your short-sightedness, around 9 out of 10 people experience a significant improvement in their symptoms.

Most people who have laser surgery report that they are happy with the results. However, it's important to realise that laser surgery may not necessarily improve your vision to the same degree as wearing corrective lenses.

And as with any type of surgery, laser surgery carries risks of complications. Read more about the complications of laser surgery.

Who can't have laser surgery?

You shouldn't receive any sort of laser surgery if you're under 21 years old because your vision will still be developing and it would be dangerous to alter the structures of your eyes at this stage.

Your vision can also change if you're over 21 years old. Your clinic should check your glasses or contact lens prescriptions to confirm that your vision hasn't changed significantly over the last two years.

Laser surgery may also not be suitable if you:

  • have diabetes – this can cause abnormalities in the eyes, which can be made worse by laser surgery to the cornea
  • are pregnant or breastfeeding – your body will contain hormones that cause slight fluctuations in your eyesight and focusing power, making precise surgery too difficult
  • have a condition that affects your immune system, such as HIV or rheumatoid arthritis – these types of conditions may affect your ability to recover after surgery
  • have other problems with your eyes, such as glaucoma (a condition that can cause blindness) or cataracts (where the lenses of the eye hardens and become cloudy)

Availability

You will usually have to pay for surgery on a private basis.

Lens implant surgery

Lens implant surgery is a relatively new type of surgery for short-sightedness. It involves implanting an artificial lens into your eye.

The artificial lens is specially designed to compensate for any defects in the cornea so that rays of light are focused more clearly on to the retina.

There are two main ways of performing lens implant surgery. They are:

  • inserting a phakic implant, which is a contact lens that's permanently inserted into your eye without removing your natural lens ('phakic' means that the eye contains its natural lens)
  • replacing the natural lens with an artificial one – this is sometimes known as refractive lens exchange

These two types of lens implant surgery are described in more detail below.

Phakic lens implant

Phakic lens implants are generally used for people who are 25 to 45 years old and aren't suitable candidates for laser surgery (for example, people with high myopia), or for those who have difficulty wearing glasses – for example, due to a disability or professional requirement.

Phakic lens implantation is the preferred technique for younger people (those under 45) because their natural, unaided reading vision is preserved.

The procedure is carried out using a local anaesthetic (painkilling medication) 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 through a small cut in the cornea.

Depending on its design, the phakic lens will be attached to your iris (the coloured part of the eye), placed in the angle between your cornea and iris, or positioned so that it floats over the surface of your natural lens.

Artificial lens replacement

Artificial lens replacement is essentially the same as cataract surgery. During the procedure, your natural lens will be replaced with an artificial lens that corrects your short-sightedness.

Refractive lens exchange is usually a day case procedure, performed under a general or local anaesthetic. The operation is not painful. You'll be able to see clearly within two days of having surgery. The second eye will usually be treated about seven days after the first.

Results

Phakic lens implants usually achieve moderately better results, in terms of improving vision on a long-term basis, than a clear lens extraction. However, the technique carries a higher risk of complications, such as cataracts.

A refractive lens exchange may be more suitable for older adults with pre-existing damage to their eyes, or an eye condition other than short-sightedness, such as cataracts or glaucoma.

Also, as both techniques are relatively new, there's little information about whether they're safe or effective in the long term. Talk to your doctor about each procedure so that you're fully aware of any risks involved.

Read more about the complications of lens implant surgery.

Complications

Complications of short-sightedness

If you have severe short-sightedness (high degree myopia), you're more likely to develop eye disorders in later life. These might include:

  • retinal detachment – the retina begins to pull away from the blood vessels that supply it with oxygen and nutrients; left untreated, retinal detachment can cause permanent vision loss
  • glaucoma – fluid builds up inside the eye which, if left untreated, can also pose a threat to your vision
  • cataracts – cloudy patches that develop inside the lens of the eye
  • macular degeneration – the central section of the retina (the macular) becomes damaged, leading to some loss of central vision

Complications of laser surgery

As with all types of surgery, laser surgery carries a risk of complications. The most common complication is dry eyes after the procedure.

Dry eyes can occur if the lasers damage the nerves that help to stimulate the production of tears. The nerves will grow back after about six months. During this time, you may find it useful to lubricate your eyes with eye drops because it will lessen the dryness and irritation.

Other complications include:

  • removal of too much cornea tissue, which could leave you with an eye that's long-sighted (where nearby objects appear blurred); this occurs in around 1 in 20 cases
  • reduced night vision – this usually passes within six weeks
  • a haze-effect around bright lights – this will usually pass within six to 12 months

More serious complications are much rarer and include:

  • the flap cut into your cornea begins to grow into the main part of the cornea when replaced (known as epithelial in-growth); this can cause problems with your vision and further surgery may be required to correct it
  • the cornea becomes too thin and your vision is reduced or lost (ectasia)
  • the cornea becomes infected (microbial keratitis)

Lens implant surgery

The most common complication of lens implant surgery is called posterior capsule opacification (PCO). This is where part of the artificial lens becomes thickened and causes cloudy vision.

An estimated half of all people who have lens implant surgery will develop PCO. It usually occurs between six months and five years after having surgery. Treatment for PCO can involve laser surgery to remove the thickened part of the lens.

Other possible complications include:

  • retinal detachment
  • cataracts
  • seeing a halo of light around objects at night
  • reduced night vision
  • glaucoma

Eye test

Going for regular eye examinations not only makes sure you can see clearly, they can also detect certain health conditions in their early stages.

Dr Susan Blakeney, advisor to the College or Optometrists, tells us about having an eye test.

Why should I have an eye examination?
There are two main functions of a sight test. Firstly, to make sure you are seeing as clearly and as comfortably as you can. Secondly, to make sure your eyes are healthy. People often presume that just because they can see properly, their eyes are healthy. If you can see well, it doesn’t necessarily mean that you don’t have any eye disease and it’s important that any eye disease is picked-up early.

What diseases are you looking for? Glaucoma is one of the main eye diseases we look for. It is more common in older people and certain ethnic groups such as African Caribbean and people of Asian decent. It happens slowly, so a person might not realise they have it until it’s quite advanced, unless they have their eyes tested.

How often should I have my eyes tested?
It’s normally at least every two years, but this can vary depending on individual circumstances. It might be more often if you have a family history of eye disease, you’re from certain ethnic groups, or you’re getting older and the risk of eye disease is greater. At the other end of the spectrum, when you’re younger, your eyes can change quickly and your spectacles may need to be brought up to date more often. It’s best to ask your optometrist when they’d like to see you again.

What happens during an eye exam?

The optometrist will:

  • Test your vision by asking you to read a series of letters on a chart,
  • check how your eyes are working together,
  • check the health of your eyes by looking inside your eyes with a special light,
  • see what spectacles you need using different lenses,
  • the optometrist may also test your side vision by asking you to look into an instrument and indicate whether you see flashing lights,
  • if you are at risk of glaucoma, the optometrist will also test the pressure inside your eyes

Will it hurt or have an effect on my eyes?
An eye exam won’t hurt and it won’t affect your vision. There’s no need to worry about coming away with blurry eyes. You can fit an eye exam in to your lunch break and drive away afterwards. You might occasionally need eye drops to enable the optician to have a better look at the back of the eyes, but you will have plenty of warning and this can be done during a later appointment.

How long does an eye exam take?
It usually takes around 20 to 30 minutes.

How do I choose an optometrist?
Like many things, it’s best to go on personal recommendation. Ask your friends, neighbours or doctor if there’s a local optometrist they would recommend. Once you’ve found an optometrist you’re happy with, it would be better to stick with them. It’s really important to get the continuity of care, in the same way you wouldn’t go to a different dentist every two years. The optometrist will have the benefit of your past clinical notes to refer to, so they’ll be able to give you a better service.

How much does an eye exam cost?
This can vary from one practice to another. There is no national guideline as to how much practices should charge for their eye exam.

Some optometrists can offer additional services such as taking a photograph of the back of your eye. There may be an additional cost for this - ask your optometrist for further details.

Some people are entitled to have their employers pay for their sight test because they have to use computers or display screens to do their job. You would need to ask your HR department to find out if you fall into this category.

Content supplied by NHS Choices