As well as a reduction of vision, you may experience other symptoms such as:

• eye pain,

• a burning, or gritty, sensation in your eyes, or

• a blurring, or distortion, of your vision.

However, symptoms such as these are usually caused by specific eye-related problems, such as:

• glaucoma (a group of eye conditions that affect your vision),

• dry eye syndrome (keratoconjunctivitis),

• cataracts (where a cloudy area forms in the lens of the eye), and

• macular degeneration (where your vision gradually begins to deteriorate over a long period of time).

Glaucoma

Chronic glaucoma

In cases of chronic (long-term) glaucoma there are not usually any noticeable symptoms because the condition develops so slowly. Your outer field of vision (peripheral vision) is affected first, and then the visual field towards the centre of your eye gradually begins to deteriorate.

As changes to vision are often linked to getting older, it is very important that you have regular eye tests. How often you need to have an eye test will vary depending on your individual circumstances and you should ask your optometrist (eye care specialist who carries out eye tests) for advice about this. However, for most people, it is recommended that they have an eye test at least every two years.

Acute glaucoma

If you have acute (short-term but severe) glaucoma, you may experience the following symptoms:

• intense pain in your eye,

• redness of your eye,

• headache,

• sore, tender eye area,

• seeing halos, or 'rainbow-like rings', around lights, and

• misty vision.

Congenital glaucoma

In cases of congenital glaucoma (where the condition is present at birth, or develops shortly after birth), the following symptoms may be present:

• large eyes (due to pressure that causes them to expand),

• sensitivity to light,

• a cloudy appearance to the eyes,

• watery eyes,

• jerky movements of the eyes, and

• a squint (where the eye turns inwards, outwards, upwards, or downwards).

Dry eye syndrome

The symptoms of dry eye syndrome can include:

• feelings of dryness, grittiness, or soreness, in both your eyes, which gets worse throughout the day,

• redness of your eyes,

• watery eyes, particularly when you are exposed to wind, and

• your eyelids stick together on waking.

Cataracts

If you have cataracts, your sight is likely to be affected by different light conditions. For example, you may find it more difficult to see:

• if the light is dim, or

• when the light is bright, such as on a very sunny day, or in bright artificial light.

Cataracts can also affect your sight in other ways including:

• the glare from bright lights may be dazzling or uncomfortable to look at,

• colours may look faded, or less clear, and

• reading, watching television, or other daily activities may become more difficult than they used to be.

Macular degeneration

The macular is located at the centre of the retina. The retina is the layer of light-sensitive tissue at the back of the eye that converts light into images and sends them to the brain.

The macular plays a very important role as it enables you to see what is directly in front of you, and allows you to see things in close-up detail and in colour.

If the delicate cells of the macula are damaged and stop working properly, your vision will be affected. This can sometimes occur as a person gets older, and it is commonly known as ‘age-related macular degeneration’ (AMD).

There are two types of AMD - dry AMD and wet AMD:

• Dry AMD - is the most common type of AMD, and it gradually causes a loss of your central vision.

• Wet AMD - is more serious than dry AMD. It often develops very quickly and is caused by new blood vessels growing behind the retina that cause bleeding and scarring. Wet AMD requires treatment as soon as possible.

Dry AMD

If you have dry AMD, you will:

• need brighter light than normal when reading,

• find it difficult to read printed or written text (because it appears blurry),

•  have difficulty recognising people's faces, or

• your vision will seem hazy, or less well defined.

Colours may also appear less vibrant.

Wet AMD

If you have wet AMD, you will have:

• visual distortions - for example, straight lines may start to appear wavy, or crooked (metamorphopsia), and

• a blind spot - which usually appears in the middle of your visual field (scotoma), and will become larger if left untreated.

You should seek immediate medical assistance if you, or someone you know, experiences any sudden changes in their vision, such as those described above.

Despite improved access to treatment over recent years, cataracts are still the leading cause of visual impairment in all areas of the world (apart from in developed countries).

In the least developed countries - in particular, those in sub-Saharan Africa (countries to the south of the Sahara desert) - the causes of avoidable blindness are:

• cataracts (50%),

• glaucoma (15%),

• corneal opacities (10%),

• trachoma (7%),

• childhood blindness (5%), and

• ochocerciasis (4%).

The World Health Organisation (WHO) is aiming to eliminate avoidable blindness by 2020 and have introduced a global initiative called ‘VISION 2020: The Right to Sight’. In particular, the strategy aims to target the six conditions listed above. 

Chronic blindness

Chronic (long-term) blindness can be caused by a number of different health conditions. For example, it can be caused by:

• cataracts - where a cloudy area forms in the lens of the eye,

• glaucoma - a group of eye conditions that affect your vision,

• age-related macular degeneration - where the vision gradually deteriorates with age (see below),

• corneal opacities - where continual scratching of the cornea (the transparent window at the front of the eye) causes it to become inflamed and then opaque (cloudy),

• diabetic retinopathy - where the tiny blood vessels that nourish the retina become damaged,

• trachoma - a bacterial eye infection, or

• childhood eye conditions - for example, those caused by vitamin A deficiencies, such as corneal scarring and visual loss.

Sometimes, blindness can also be caused following injury, or trauma, to the eyes.

Age-related macular degeneration (AMD)

In the UK, age-related macular degeneration (AMD) is the most common cause of visual impairment among older people.

About 2% of people who are over 50 years of age have AMD, with the number rising to 8% for those who are over 65 years of age, and 20% for those who are over 85 years of age.

The exact cause of AMD is unknown. However, a number of risk factors have been identified that will increase your chances of developing the condition. These are listed below.

• Age - as you get older your chances of developing AMD increase.

• Sex - women are more likely to develop AMD than men.

• Genetics - a number of genes have been identified which if inherited (passed on from a family member) may increase your likelihood of developing AMD.

• Smoking - if you smoke, you are more likely to develop AMD.

• Sunlight - prolonged exposure to sunlight may affect your retina. To protect your eyes, you should always wear a pair of good quality sunglasses in bright sun-lit conditions.

Vitamin and mineral supplementation

Certain types of vitamins and minerals may also provide some protection against the effects of AMD.

For example, studies have shown that dietary supplements that contain high amounts of vitamins A, C, E, and beta carotene may help to slow down the progression of AMD. The minerals zinc and copper have also been shown to have a positive effect.

However, vitamin and mineral supplementation should only be carried out on the advice of a doctor, or eye care specialist, and it is only recommended for people who are classed as being at high risk, such as those who already have AMD in one eye, or both eyes.

Basic eye test

When you go to have an eye test, your optometrist will carry out a number of different tests in order to check your vision and the overall health of your eyes. The types of test that you may have are described below.

Snellen test

A basic sight test - known as a Snellen test - is often used to determine how good your vision is, and to pick up any possible problems with your eyes.

The Snellen test involves reading rows of letters from an illuminated chart that become progressively smaller on each line. Your optometrist will take into account how far away from the chart you are when taking the test.

If you are taking a Snellen test for the first time, you may be asked not to use your glasses or contact lenses. However, if you have taken the test before, and you wear prescription glasses, or contact lenses, your optometrist may ask you to take the test while you are wearing them.

Further eye tests

If you do not currently wear glasses, or contact lenses, and your optometrist decides that you need to wear them, you will need to have further tests to determine what kind of glasses (or lenses) you need. During these tests, you will be asked to wear a number of special lenses and to look at various charts displaying different letters and colours.

During your eye test, your optometrist will also look for signs of eye conditions, such as glaucoma (a progressive eye condition) and diabetic retinopathy (damage to the tiny blood vessels that nourish the tissues of the eye). They will do this by shining a light into your eyes in order to see how well they react to light.

At the end of your eye test, your optometrist will discuss the results with you, and advise you about the best course of action. They will also either give you with a certificate to confirm that you do not need to wear glasses, or contact lenses, or they will give you a prescription for the type of glasses, or lenses, that you need. The prescription can be used at any optician.

Registering as blind or partially sighted

If, during your sight test, you are only able to read the top line of the eye chart, you may be eligible to register as blind, or partially sighted. To do so, you will need to be referred to an ophthalmologist (a specialist in diagnosing and treating eye-related conditions) by your GP, or optometrist.

After carrying out further tests, the ophthalmologist will write to your local social services department to confirm that you have been diagnosed as blind, or partially sighted. You may also be registered as blind, or partially sighted, if you are able to read the first three lines of the chart, but you have a severely restricted field of vision (you are unable to see to the side).

Other vision tests

If you have a high risk of developing eye conditions, such as glaucoma, or diabetic retinopathy, or if your optometrist has found signs of these conditions, you may need to have some more vision tests. Some of the vision tests that you may need to have are described below.

Visual field test

A visual field test is used to measure your peripheral (sideways) vision using a piece of equipment called a visual field screener. During the test, you will be asked to look at a small point in the middle of the screen (while keeping your eye still).

At random intervals, a light will flash on and off at different places on the screen around the central point. Each time you see the light flashing, you will be asked to respond by pressing a buzzer. The lights may also be of varying brightness.

The test will then be repeated with the other eye covered. It usually takes about 45 minutes to complete.

Tonometry

Tonometry is often used to test for eye conditions such as glaucoma. It involves using an instrument called a tonometer to measure the pressure inside your eyeball.

The optometrist or ophthalmologist will hold the tonometer close to your eye and will press a button to release a small puff of air against your eyeball. The tonometer has sensor which measures how much indentation the air has caused. The procedure is painless, but it may cause a very small amount of discomfort.

Ophthalmoscopy

Ophthalmoscopy is a test that is sometimes used by an ophthalmologist to examine the inside of the eye in detail, including the optic nerve. The ophthalmologist will use a small torch to look closely at your eyeball so that they are able to identify any abnormalities.