A-Z of Eye Health
A-Z of Eye Conditions
Acanthamoeba Keratitis is an infection of the cornea, the clear 'window' at the front of the eye, that can be very painful. The infection is caused by a microscopic organism called Acanthamoeba, which is common in nature and is usually found in bodies of water (lakes, oceans and rivers) as well as domestic tap water, swimming pools, hot tubs, soil and air.
Many different species of Acanthamoeba exist. Acanthamoeba organisms do not generally cause harm to humans (we come into contact with them when we wash, swim, drink water etc), but they can cause a serious eye disease if they infect the cornea. Not all species of Acanthamoeba have been found to cause corneal infections. AK is most common in people who wear contact lenses, but anyone with a corneal injury is susceptible to developing the infection.
Age-related macular degeneration (AMD)
Age-related macular degeneration involves damage to the macula and affects central vision.
The macula is a small, but extremely important area located at the centre of the retina, the light-sensing tissue that lines the back of the eye. It is responsible for seeing fine details clearly.
If you have AMD, you lose the ability to see fine details, both close-up and at a distance. This affects only your central vision. Your side, or peripheral, vision usually remains normal. For example, when people with AMD look at a clock, they can see the clock's outline but cannot tell what time it is; similarly, they gradually lose the ability to recognise people's faces.
There are two types of AMD. Most people (about 75%) have a form called "early" or "dry" AMD, which develops when there is a build-up of waste material under the macula and thinning of the retina at the macula. Most people with this condition have near normal vision or milder sight loss.
A minority of patients with early (dry) AMD can progress to the vision-threatening forms of AMD called late AMD.
The commonest form of late AMD is "exudative" or "wet" AMD. Wet AMD occurs when abnormal blood vessels grow underneath the retina. These unhealthy vessels leak blood and fluid, which can prevent the retina from working properly.
Eventually the bleeding and scarring can lead to severe permanent loss of central vision, but the eye is not usually at risk of losing all vision as the ability to see in the periphery remains. There is a rarer form of late AMD called geographic atrophy, where vision is lost through severe thinning or even loss of the macula tissue without any leaking blood vessels.
Amblyopia (lazy eye)
Amblyopia develops in childhood and results in reduced vision in one eye. It happens when one eye is used less than the other from birth to seven years of age, which leads the brain to prefer the better eye.
Amblyopia can be caused by:
- A turn in the eye (a strabismus or squint)
- A difference in the glasses prescription between the two eyes
- An obstacle blocking visual stimulation to the eye, such as a droopy eyelid or cataract (cloudy lens); the amblyopia might persist even after the obstacle has been removed.
Astigmatism is a common and treatable eye condition. The front surface of a normal eye is round like a football, but people with astigmatism have eyes shaped more like an oval rugby ball. This changes the path of light so that the image formed at the back of the eye is not sharply focused.
People with astigmatism will usually also be short or long sighted. People can be born with astigmatism or it can develop later in life. Many people have a little astigmatism and their sight is unaffected. If the astigmatism is more severe, you might notice:
- Blurring and distortion of near or far-away objects
- Headaches when trying to focus
- Tired eyes
Blepharitis is inflammation of the rims of the eyelids, which causes them to become red and swollen. It is a common condition which can develop at any age but is more common in young children and people over 50. Most people experience repeated episodes followed by periods with no symptoms. It is not possible to catch blepharitis from someone else who has it.
A cataract is clouding or opacity of the lens inside the eye. It causes gradual blurring of vision and often glare.
Inside your eye, behind the iris and pupil is a lens. In a normal eye, this lens is clear. It helps focus light rays on to the back of the eye (the retina), which sends messages to the brain allowing us to see.
Cataract usually forms slowly and most people experience a gradual blurring of vision.
Charles Bonnet syndrome
Charles Bonnet syndrome (CBS) is a common condition among people who have lost their sight. It causes people who have lost a lot of vision to see things that aren't really there, known as visual hallucinations.
People who have CBS may have lost a lot of their vision from an eye condition, such as age-related macular degeneration, cataract, glaucoma or diabetic eye disease. Many of these conditions are more common in older people so many people who have CBS are older.
Conjunctivitis is a common condition which causes the surface of your eye to go red and, often, sticky or watery and your eye becomes sore.
Conjunctivitis can be caused by infection from bacteria, viruses or other organisms, and also by allergy or inflammation.
Viral conjunctivitis tends to cause a watery red eye and can last for two to three weeks even with the correct treatment. In most cases viral conjunctivitis does not affect your vision but rarely you might notice your vision becomes blurry or you may see glare when looking at lights. This is due to an inflammatory reaction causing small white dots on the cornea, the transparent window at the front of the eye.
These usually fade with time, but it can take a few weeks or even months. Bacterial conjunctivitis is more likely to cause a red eye with a sticky yellow discharge. There is no antiviral medication for viral conjunctivitis and it does not respond to antibiotic drops as it is not caused by bacteria.
The best treatment for viral conjunctivitis is to use artificial tears and simple painkillers, with regular lid cleaning and cold compresses. The conjunctivitis disappears when your body becomes immune to the virus and fights the germs off, just as in a cold or 'flu. Very rarely, steroid drops are given for severe cases of viral conjunctivitis or when the cornea is affected.
Antibiotic drops can be helpful in cases of bacterial conjunctivitis and are often prescribed for a one or two-week course.
Contact lenses should not be worn during any type of conjunctivitis.
Corneal abrasions are a small scratch on the cornea, the clear window at the front of the eye. They are generally a result of trauma (injury) to the surface of the eye. Common causes include a fingernail scratching the eye, walking into something, and getting grit in the eye, particularly if the eye is then rubbed. Injuries can also be caused by contact lens insertion and removal.
Abrasions are very painful because there are many nerves that supply the cornea. The pain gets better as your eye heals, but this can take between 24 and 48 hours. If the abrasion involves the central part of your cornea, your vision could also be temporarily affected. Apart from the pain, your eye might be watery, red and sensitive to light.
If your eye becomes increasingly red or painful after treatment or your sight becomes much more blurred, you should see an eye doctor again or contact the hospital.
Diabetic retinopathy is a complication of diabetes, and causes damage to the blood vessels in the retina.
Many diabetics – particularly those with poor diabetic control which results in too-high blood sugar levels over long periods of time – have damaged blood vessels in the retina, the tissue lining the back of the eye that detects light and allows us to see. This condition, called diabetic retinopathy, affects up to eight out of 10 patients who have had diabetes for 10 years or more.
Many people with mild diabetic retinopathy have good vision, but there are two types of sight-threatening diabetic retinopathy: diabetic macular oedema (DMO) and proliferative diabetic retinopathy (PDR).
In DMO, fluid leaks out of the tiny damaged blood vessels in the back of the eye, and accumulates in the macula, the central part of the retina which is responsible for seeing fine details and central vision. This leads to swelling of the tissue and blurred vision. Eventually, patients with diabetic macular oedema can develop poor central vision and be unable to read or drive, but the vision to the side usually remains normal.
Proliferative diabetic retinopathy (PDR) is when the retinal blood vessels close resulting in the retina being starved of blood. This causes abnormal and very fragile blood vessels to grow on the surface of the retina which can lead to permanent loss of vision from bleeding into the eye, retinal scarring and retinal detachment.
Double vision, diplopia, is seeing two images of a single object. The two images may be one on top of the other, side by side, or a mix of both.
Double vision may be constant, it may come and go, or it may only occur when you're looking in a particular direction.
The cause of your double vision depends on whether your double vision is coming from one eye (monocular) or both eyes (binocular). This also affects which treatment you receive.
Treatment ranges from special glasses and eye exercises, to surgery to remove a cataract.
Dry eye is an eye condition caused by a problem with tears. Dry eye can make your eye feel dry, scratchy, irritated and uncomfortable. Dry eye is caused by a problem with your tears. When you blink you leave a thin layer, called the tear film, over the front of your eye.
The tear film keeps the front of your eye healthy and it also helps the eye focus properly, giving you clear vision. The tear film is a complicated structure made up of three layers. If you don't produce enough tears, if your tears aren't of the right quality or your tears aren't spread across the front of your eye properly then you may develop dry eye.
Dry eye is usually a natural symptom of getting older. As you get older your eyelids are less effective at spreading the tears each time you blink. The various glands in your eye that produce the three layers of the tear film become less effective, so the quality of your tear film is affected as you get older.
Endophthalmitis is an inflammation of the internal eye tissues, most commonly caused by an infection.
If you have recently had an operation on your eye, a procedure such as an intravitreal injection or an injury to your eye and you experience any of the following symptoms, please report immediately to your nearest eye accident and emergency department:
- Sensitivity to light
- Vision reduction
The earlier the eye is treated, the better the recovery.
The main danger is the risk of eyesight being reduced or lost if treatment is not started as early as possible.
Flashes and floaters
Flashes of light or black floaters that look like spiders or tadpoles and move around as you move your eye are quite commonly seen by people with normal eyes.
They happen because of changes in the vitreous, the clear, jelly-like substance that fills the inside of your eyeball. The vitreous jelly shrinks as you get older, and slowly pulls away from the inside surface of the eye. This shrinking and separation or detachment of the vitreous from the retina is a common phenomenon, particularly in people over 50 years of age, and causes no retinal damage in nine out of 10 patients. It is known as a posterior vitreous detachment.
Flashes and floaters rarely lead to any serious complications, so you generally don’t need any treatment for them. If they are troublesome, the effect of floaters might be minimised by wearing dark glasses. This will help especially in bright sunlight or when looking at a brightly lit surface. In many cases, the flashes disappear with time and the floaters get less noticeable as your brain adjusts to the jelly change.
If your flashes or floaters become much worse, you should consult your GP, your optometrist (optician) or visit your local A&E department to exclude any serious problems. If you see a black shadow or curtain effect or you suddenly lose vision, you should go to your nearest A&E without delay.
Glaucoma is the name given to a group of eye conditions in which the optic nerve is damaged where it leaves the eye.
Glaucoma is the name given to a group of eye conditions in which the optic nerve is damaged where it leaves the eye. Although any vision which has been lost to glaucoma cannot be recovered, with early diagnosis, careful monitoring and regular use of the treatments, further damage to vision can be prevented and most patients retain useful sight for life. While there are usually no warning signs, regular eye tests will help detect the onset of the disease.
Glaucoma is one of the world's leading causes of blindness. In the UK, about two per cent of the population over 40 have the condition. Glaucoma involves loss of vision due to damage of the optic nerve. The optic nerve carries sight images to the brain and any damage to the nerve results in damage to sight.
For the eye to work properly a certain level of pressure is needed for the eye to keep its shape but if the eye pressure gets too high, it squeezes the optic nerve and kills some of the nerve fibres, which leads to sight loss. The first areas to be affected are the off-centre parts of the vision. If the glaucoma is left untreated, the damage can progress to tunnel vision and eventual loss of central vision, although blindness is rare.
Usually, but not always, the damage occurs because pressure within the eye increases and presses on the nerve, which damages it.
Hypermetropia is when people cannot see clearly close up without glasses or contact lenses.
It is a common problem with the eye’s focusing that can affect your vision at all distances, but especially close-up.
Usually, light comes in through the lens and focuses on the retina at the back of the eye. In hypermetropia, the light is focused too far back in the eye, behind the retina, which causes things to look blurred close-up.
Many very young children have mild hypermetropia that gets better by itself as they grow older.
The percentage of people with hypermetropia increases with age.
Long sight can be easily corrected with glasses or contact lenses, using convex (curved outwards) lenses, which move the focus of the light forward onto the retina, allowing you to see clearly.
Keratoconus is an eye condition in which the normally round dome-shaped clear window of the eye (cornea) progressively thins causing a cone-shaped bulge to develop. Exactly why this happens is unknown, but genetic factors play a role and it is more common in people with allergic diseases such as asthma, in Down's syndrome and in some disorders of connective tissue such as Marfan's disease. It affects up to one in 1,000 people and is more common in people of Asian heritage. It is usually diagnosed in teenagers and young people.
The change in shape and thinning of the cornea and, in later stages, scarring causing loss of transparency of the cornea impairs the ability of the eye to focus properly, causing poor vision.
A macular hole is a small hole in the macula which is in the centre of the retina. Think of your eye as a camera, the retina is like the photographic film. It is a very thin layer of tissue, which is sensitive to the image focused on it, and sends the information to the brain.
At the very centre of the retina is the macula. This is a very special area of the retina, which we use for reading and recognising complex shapes. Sometimes, a hole forms in the macula, which prevents it from working normally. This affects your vision, particularly for reading and other visually demanding tasks, but it does not cause total blindness.
Myopia, often known as "being short sighted", causes your vision to be blurry in the distance but clearer when looking at things up close. It’s a very common condition and for most people it can easily be dealt with using contact lenses or glasses, which will make your vision clear and crisp.
This is because of a focusing problem. Usually, light comes in through the lens and focuses on the retina at the back of the eye. In myopia, the light is focused too far forward in the eye, in front of the retina, which causes things to look blurred in the distance.
About three in 10 people in the UK are short-sighted and about 5% of those have severe myopia.
People typically become short-sighted in their teenage years or twenties. Several factors probably combine to cause myopia. There is a tendency for myopia to run in families. Myopia usually appears around puberty, but can appear at any age from early childhood.
In most cases, myopia stabilises in once the body is fully grown, usually in the mid-twenties or earlier.
A widely held misconception is that myopia corrects itself with age. Although patients with low-level myopia can read without glasses throughout life, their distance vision remains poor.
Presbyopia causes a loss of reading vision due to age.
The natural lens, which is the flexible element of focus in the eye, enables most young people to see clearly in the distance and up close. Flexibility of the natural lens diminishes with age, and by the mid-forties, even people who have never previously needed spectacles start to need reading glasses.
This age-related loss of reading vision is called 'presbyopia'.
Retinal detachment occurs when the thin lining at the back of your eye begins to pull away from the blood vessels that supply it.
The retina is a thin layer of nerve cells that lines the inside of the eye. It is sensitive to light (like the film in a camera) and you need it to be able to see properly.
Retinas detach because they have one or more holes in them, which allows fluid to pass underneath them. This fluid causes the retina to become separated from the supporting and nourishing tissues underneath it. Small blood vessels might also be bleeding into the vitreous (the jelly-like substance in the centre of the eye), which might cause further clouding of the vision.
Without treatment, a retinal detachment usually leads to blindness in the affected eye.
Strabismus is the medical term of a squint, a condition where the eyes point in different directions. One eye may turn inwards, outwards, upwards or downwards while the other eye looks forward.
Squints are common and affect about one in 20 children. They usually develop before a child is five years old, but can appear later, and adults can also be treated for the condition.
The most obvious sign of a squint is eyes that look in different directions. Squints can also cause: double vision; lazy eye(amblyopia) in young children where the vision is poor in the eye with the squint; and a squint can cause people to develop an abnormal position of the head.
If a squint is left untreated in young children, lazy eye (amblyopia) can develop. The vision in the affected eye gradually deteriorates because the brain ignores the weaker message being sent from that eye. A lazy eye can be treated up until about six or seven years of age, but it is important that it is treated as soon as possible.
A stye is a small abcess (painful collection of pus) on the eyelid and is an infection at the root of an eyelash. It appears as a small painful red lump, often with a yellow spot in the middle, on the outside of the eyelid.
Other symptoms include a watery eye and a red eye or eyelid. It's not always necessary to see a doctor if you develop a stye, although if you have a painful and very swollen eyelid with a stye, you should have it checked.
Most styes get better without treatment within a few days or weeks. Styes may burst and release pus after three or four days. A warm compress (a cloth warmed with warm water) held against the eye encourages the stye to release pus and heal more quickly.
Further treatment is not usually needed unless you have a very painful stye that is not getting better or a very swollen red lid indicating spreading infection. In this case, see your doctor who may decide to treat it with antibiotics, drain it or refer you to an ophthalmologist. You should never attempt to burst a stye yourself.
Uveitis is an eye condition where there is inflammation (swelling) in a part of your eye called the uvea. Uveitis affects different people in different ways depending on which part of the uvea is affected. The symptoms of uveitis may include pain, sensitivity to bright lights and poor vision. Most cases of uveitis get better with treatment. Some types of uveitis are more difficult to treat and may cause more permanent changes to your vision.
Around two to five in every 10,000 people are affected by uveitis in the UK every year. Uveitis affects people of any age, but most commonly between the ages of 20 and 59 years. Some children develop uveitis.
Get it in perspective
We have two eyeballs in order to give us depth perception - comparing two images allows us to determine how far away an object is.