Refractive errors (myopia, hyperopia, astigmatism and presbyobia)

What are refractive errors?

Refractive errors are range of common conditions in which variations in your eye shape stop light from focusing correctly on the retina, the light-sensitive layer at the back of the eye. You can be short-sighted (myopia), long-sighted (hyperopia), or have astigmatism or presbyopia. 

What are the different types of refractive errors?

Refractive errors can be one of four different conditions – all of which make it harder to see clearly. The different types are:

Short-sightedness (myopia)

Short-sightedness (myopia) is a common refractive error where distant objects appear blurred. It happens when light focuses just short of the retina, usually because the eyeball is too long. Myopia often runs in families and is also more common in people with a Far Eastern heritage.

Research suggests that too much close-up work can cause short-sightedness, which often develops or worsens during the teenage years. Spending too little time outdoors during childhood is another important risk factor.

Myopia can develop in later life, too, including because of other eye conditions, such as cataracts.

Severe short-sightedness (high myopia) is associated with an increased risk of retinal degeneration (myopic maculopathy) or retinal detachment – a medical emergency that requires urgent treatment.

Long-sightedness (hyperopia)

Long-sightedness, or hyperopia, is the most common refractive error. It makes close-up objects appear blurry, especially when reading for a long time. It happens when light focuses too far beyond the retina - either because the front of the eye isn’t curved enough or the eyeball is slightly short. 

Long-sightedness also often runs in families and tends to be more common in people with a European heritage. Babies are often born with some degree of hyperopia, but most will grow out of it by around age two as their eyes develop. Children with severe long-sightedness are more likely to develop other eye problems, such as squint or amblyopia (or ‘lazy eye’).

Presbyopia

Everybody gets presbyopia as they get older. As you age, the lens inside the eye gets harder and less flexible, which makes it harder or impossible to correctly focus light on the retina – causing close objects to appear blurry.

Presbyopia usually develops after the age of 40 to 50. People with a combination of short-sightedness and presbyopia may still be able to read by taking their glasses off.

Astigmatism

Astigmatism can make both distant and close objects look blurry or distorted. It happens when the front of the eye is not evenly curved – so it is shaped a bit like a rugby ball rather than a football. As a result, light bends differently as it enters the eye

It causes more than one focal point on the retina, which makes certain areas of your field of vision look blurry.

As with long-sightedness, astigmatism is common in babies but often corrects itself as the eye develops. Many people also develop the condition as children or young adults, particularly after an eye injury or surgery. It often occurs alongside short or long-sightedness.

What causes refractive errors?

Refractive errors are mainly caused by small variations in the shape of the eye. These changes aren’t noticeable without close-up examination, but they are significant enough to affect how light is focused on the retina as it passes through the eye.

Causes of refractive error can be:

• Genetic: Refractive errors can run in families.
• Lifestyle: Growing evidence shows that too much close-up work and insufficient time spent outdoors can contribute to certain refractive errors.
• Ethnic background: There is a higher prevalence of refractive errors among specific populations, although this is thought to reflect differences in lifestyle.

A refractive error can occur because of one or some of the following variations or changes that affect the shape of the eye:

• Eyeball length: The eyeball is too long or too short, which can prevent the light entering the eye from focusing on the retina correctly.
• Irregular cornea: The cornea, which is the clear window at the front of the eye, is not curved equally in all directions, and it can’t focus the light onto the retina correctly.
• Ageing of the lens: The lens, which sits in the middle of the eye and helps to focus light onto the retina, becomes stiffer as we age – which may cause the eye to struggle to focus during daily activities.

What are the signs and symptoms of refractive errors?

Symptoms can vary depending on the type of refractive error and its severity. The most common symptom is blurred vision. Some people will experience very mild symptoms that are only noticeable during tasks that require a lot of focusing, such as reading, using a computer, or driving. Common symptoms of refractive errors include:

• Problems with focusing and seeing details: for example, when reading or looking at a computer.
• Blurred vision: This may affect distant or close-up objects or even both.
• Double vision: Seeing two images when looking at a single object.
• Headaches: Trying harder to focus and adjust the eyes often causes headaches.
• Eye strain: When the eyes feel tired or sore, particularly when performing tasks involving lots of focus.
• Squinting: This can be a sign that somebody’s having to work harder than normal to focus their vision.
• Seeing a glare or halo around bright lights: This is a result of diffraction, an effect that occurs when the light bends while entering the eye.

Children often aren’t aware there’s a problem with their vision as they may never have known any different. So it’s essential to look for possible signs they’re struggling to see clearly – such as sitting close to the television, squinting, or rubbing their eyes. 

Are refractive errors serious?

Refractive errors can be mild, causing only mild eye strain or the inconvenience of having to wear glasses or contact lenses. However, they can be more serious. Severe short-sightedness (high myopia) is associated with an increased risk of retinal degeneration (myopic maculopathy) or retinal detachment – a medical emergency that requires urgent treatment.

Early diagnosis is particularly important for children because it may impact their educational progress. And if they are not addressed promptly, it can affect the development of their eyesight and other conditions, such as amblyopia (lazy eye), might develop.

How are refractive errors diagnosed?

A refractive error is usually diagnosed during a routine eye examination. An optometrist will assess your ability to focus on both near and distant objects, which will help determine what type of refractive error you may have and how much it affects our eyesight. They will also examine how well your eyes work together and how they react to light.

What are the treatments for refractive errors?

If a refractive error is very mild, treatment may not be required, as your eyes may be able to adjust. However, working too hard to focus can cause eye strain and headaches, so treatment may still be necessary. The most common treatments are:

• Glasses or contact lenses: These will help correct blurred vision and may be required all the time or just to wear while carrying out certain tasks, like reading and driving. An optometrist will prescribe the right glasses or contact lenses to achieve the clearest possible vision. Some people find their vision worsens as they age and may need stronger prescriptions. For refractive errors associated with ageing, reading glasses can help.

  It's really important for young children to get appropriate treatment (usually glasses) as not correcting refractive errors while their eyes and brains are still developing may lead to problems later on. For their brains to ‘learn’ how to see correctly, both eyes need to be working clearly and equally.

• Surgery: For adults with more severe refractive error, some types of surgery, like laser eye surgery, can correct the shape of the cornea. However, this isn’t suitable for everybody and will usually need to be paid for privately. Short-sightedness is sometimes also treated with surgery to replace the lens with an artificial one. This relatively new procedure can be very effective but isn’t always suitable for everyone.

What research is there into refractive errors?

Fight for Sight’s goal is to help further the understanding of refractive error and use this knowledge to develop prevention techniques and better treatments. We're funding several projects, including:

• A genetic test for myopia: A research team at Cardiff University has developed a genetic test that will identify an increased risk of myopia.
• Research on short-sightedness in children: Dr. Horwood’s team at the University of Reading found that 4 in 10 children with normal eyesight focus at the wrong distance for seeing close work clearly.

See our research projects