Visual Problems

Most people are concerned about problems affecting their eyes, particularly those affecting their ability to see clearly. This leaflet describes most conditions affecting the eye which can affect vision, either temporarily or permanently, and explains how they present and what can be done about them.

Visual loss can be partial (meaning the vision is impaired or hazy) of complete (meaning all or part of the vision in one or both eyes is too poor for useful function). It may occur with or without pain, suddenly or gradually, and all of these things are clues as to the cause. Some, but not all, visual loss is permanent and some, but not all, can be prevented.

What is your eye?

The eye is a ball in a bony socket, moved by muscles. Medically the whole of the eye is referred to as the globe bceause of its spherical shape. This globe has a transparent 'front window' (the pupil), and a series of magnifying parts - the clear window of the eye (the cornea), the fluid inside the eye, and the lens all play a part in magnifying. Then, at the back is a light-sensitive membrane called the retina, which sends information into the brain. This membrane is fed by a delicate network of blood vessels, called the choroid.

Problems arising in different parts of the eye can affect vision: generally speaking, the further towards the back of the eye that problems occur, the more likely they are to have a long-lasting or permanent effect on your eyesight.

Causes of sudden painful visual impairment

There are several problems which can affect the surface of the eye which can affect vision, although usually they mainly cause pain and redness. However, if severe they can cause permanent scarring of the clear window (cornea) which sits over the coloured part of the eye (the iris) and the pupil.


Conjunctivitis is inflammation or infection of the surface layer of the eye (the conjunctiva). The patient has red itchy eyes, which may be sticky if the eyes are infected. Most conjunctivitis does not affect vision but some forms, particularly viral conjunctivitis, can be severe and can spread to the cornea. Whilst rare, this can cause permanent scarring of the clear corneal tissues.

There is no curative treatment for viral conjunctivitis, which can take up to eight weeks to clear. However, the eyes need to be kept lubricated and antibiotic ointment is used to prevent secondary germ (bacterial) infection.

Foreign bodies - something in your eye

If you get something in your eye then your eye will water, the blinking reflex will be activated and your eye will be very irritable. Foreign bodies in the eye don't normally damage vision, but they can do so in certain circumstances:

Active chemicals, such as strong acid, alkali or plaster dust, may damage the surface of the eye and cause scarring. If chemicals get into your eye, you need to rinse your eyes very thoroughly and seek medical advice.

Penetrating injuries to the eye also affect vision. The eye is pretty tough and it's not easy for anything to penetrate its globe - but high-speed fragments from drilling or grinding can occasionally do so. This is not always painful - you may even not know it's happened. However, infection can then get right into the eye, which can permanently damage vision. If you think something flew into your eye whilst drilling or grinding it is important to have your eye properly examined by an eye doctor.

This serves to underline, powerfully, the need to protect the eyes when working with chemicals or with high speed drills and cutting instruments.

Corneal scratches

The cornea is very, very sensitive and if it is scraped it hurts. Eyes are red and watery, vision is blurry and it may feel as though there is something in your eye.

The layers of clear cells that form the cornea can spread to fill in a shallow scratch over about 24 hours, and they usually heal quickly. (Your eye will usually need to be padded shut for this to happen, so that healing is undisturbed.)

Deeper scratches, such as can be formed by contact lenses which are not well looked-after or cleaned, can leave a permanent scar which can permanently affect vision.

Corneal ulcers

The surface of your eye can become infected with cold sore virus (herpes simplex) and this can cause an ulcer on the surface of your eye. This causes redness, soreness and blurred vision. The pain can be very intense but the diagnosis can only be made by a doctor or nurse who stains your eye in order to see the ulcer. The treatment of these type of ulcers is with antiviral eye drops, and vision is not usually permanently affected.

Arc eye, snow blindness and photokeratitis

Photokeratitis is sunburn of the cornea. This is usually noticed several hours after exposure to the sun. Eyes are watery and feel gritty. Treatment is symptomatic. Cool, wet compresses and anti-inflammatory eye drops can be soothing. Eye protection such as eyepatches and sunglasses is helpful. Avoidance of light for two to three days is usually needed to settle things down.

Snow blindness is common in mountaineers and skiers who forget their sunglasses. The brightness of white snow reflecting the sunlight is one factor. Another it the thinner atmosphere up at altitude which reduces protection from the sun's rays.

Arc eye is a similar condition from exposure to the bright light of an arc lamp, and for this reason operators of these tools normally wear dark goggles.

Optic neuritis

Optic neuritis is uncomfortable, even painful (particularly on eve movements), and it can cause visual loss. This is sudden and may be partial or complete. Patients sometimes describe their vision as disturbed or blackened. It can also cause loss of colour vision whilst vision is maintained. Optic neuritis is caused by inflammation of the optic nerve in the eye, and it can involve one or both eyes. It can be a recurrent condition and there may be no underlying reason for it.

Multiple sclerosis (MS) is one possible cause, so if you have more than one attack of optic neuritis you will normally be offered testing to rule out MS. Other possible causes include Lyme disease, ulcerative colitis, and systemic lupus erythematosus (SLE - often just called lupus).

Optic neuritis usually resolves slowly by itself over a period of weeks or months, although vision may never return absolutely to normal.

Ophthalmic shingles

This condition occurs when shingles affects the eye and eye area. Shingles is better known for causing a painful one-sided blistering rash on the body, but can occasionally affect the eye. When it does so, the eyelid and surface of the eye become very inflamed and blistered, and the eye is watery and red, Sometimes the internal structures of the eye are also affected - this is called uveitis.

Shingles of the eye can cause visual worsening or visual loss. if the condition is not treated promptly and well then permanent scarring can occur inside the eye. In addition, after a bad attack of ocular shingles, you can be at risk of sudden-onset (acute) glaucoma (see below).

Acute glaucoma

Acute glaucoma is a sudden rise in the pressure inside the eye. This causes severe pain, often bad enough to cause you to be sick (vomit), with redness, watering and blurred vision. Patients often describe seeing rainbows around lights. The front of the eye can look cloudy and the pupil can look misshapen. The eye is said to feel as hard as a stone to touch.

Acute glaucoma is an emergency, as if it is not treated then the pressure on the nerves at the back of the eye can damage them beyond recovery, and the vision can be permanently lost.


Uveitis is a general term for inflammation of any or all of the structures in the eye. This means anything from the coloured part of the eye (the iris) backwards as far as the retina, including the rich layer of blood vessels which supplies the retina with nutrients. Uveitis causes a painful red eye. Vision is affected to differing degrees, depending on how far back the inflammation goes and how severe it is.

Anterior uveitis, involving mainly the iris, is the least serious, but all types of uveitis can cause scar formation inside the eye and damage to the retina, with loss of vision. Many conditions can cause uveitis, including infection, injury and autoimmune diseases such as ankylosing spondylitis, although sometimes the cause is unknown.


Ocular toxocariasis is a rare infection in humans, but it can cause permanent damage to the retina and loss of vision. Toxocara - also called dog roundworm - is a dog parasite which is widespread throughout the world. It usually causes no particular symptoms in dogs, but it can be spread fairly easily to humans, who usually catch it through contact with the stools (faeces) of infected dogs. Toxocariasis is one of the reasons for strong public health campaigns for dog owners to clear up their dog waste. It is possible, although unusual, to be infected simply by stroking an infected dog's fur, as the parasite eggs can be in the fur. Once we ingest them the worm develops in the liver, in the lungs and - most importantly for this article - in the back of the eye.

Toxocara eye infection usually occurs in children and the eye is usually red and painful with reduced vision, intolerance of light, and dark spots called 'floaters'. Patients are treated with medication to kill the worm plus anti-inflammatories for the eye, since much of the damage is caused by the inflammatory reaction to the worm. Some permanent damage to an area of the vision usually results.

Occasionally, old toxocara scars of undiagnosed past infection are found in the eye by chance.


Endophthalmitis is a term for a catastrophic eye infection - that is, bacterial infection of the globe of the eye internally, usually following perforating injury or after surgery. It is essentially an extreme form of uveitis and it needs urgent treatment if vision is to be saved.

Causes of sudden painless visual impairment

Sudden loss of vision is always frightening, perhaps even more so when it is painless, as there is then no obvious cause. The cause of sudden painless visual loss, however, is usually to do with the retina or with the blood vessels that serve it. Either they block, and cut off its blood supply, or they bleed, and block the ability of the retina to 'see out' of the pupil.

Brain causes can also produce painless visual loss, including migraines, strokes and, very rarely, brain tumours.

Retinal detachment

The retina is the light-sensitive membrane at the back of the eye. It is attached in place by the network of blood vessels that feed it. In retinal detachment, the retina pulls away from its fixings and, in the process, becomes detached from its blood supply. When this happens the retinal cells die quickly and vision is lost. Retinal detachment is more common in short-sighted people, who tend to have longer eyeballs. It is more common in middle age than in old age, although it can occur after eye surgery for cataract removal.

The most common symptom is a shadow spreading across the vision of one eye. People say it is like a grey curtain coming down. Prior to this there may be warning signs, including light flashes at the edge of vision, a feeling of vague heaviness in the eye and a sudden increase in showers of dark spots (floaters). These symptoms are never painful.

Many people experience flashes or floaters without retinal detachment, but if floaters are severe or suddenly worse then you should have the back of your eye examined by a specialist. The retina can be lasered back into place - but if more than 24 hours passes, it is usually beyond rescue and vision is lost.

Blockage of blood vessels at the back of the eye (retinal vein and artery occlusion)

The retinal artery supplies the retina with oxygen, and the retina is demanding and needs a good supply. If the retinal artery or one of its smaller branches blocks then the area of the retina it supplies quickly stops working. The loss of vision which results usually happens very suddenly with little or no warning. Some people may experience short periods of sight loss before the sight loss becomes permanent. The main cause of arterial blockage (occlusion) is partial blockage of larger arteries by cholesterol and fats (a condition known as atherosclerosis). Treatment of this condition is not usually very successful, and the visual loss is often permanent.

If a vein rather than an artery is blocked, the vision is lost more slowly and sometimes laser treatment can be used to prevent things from getting worse. Veins carry blood Away from the retina, so blockage of a vein only interrupts the supply gradually as the back pressure builds up from blood being unable to escape. This is rather like a sink flooding when the U-bend is blocked. Eventually, blood leaks out of the veins under pressure into the retina and its delicate structure may be permanently damaged.

Vitreous haemorrhage

This condition of sudden visual worsening or loss is caused by bleeding inside the eye. The jelly-like substance that fills the eye is called vitreous humour, and when bleeding occurs into it light can no longer get through and vision, so the affected eye goes totally dark. In itself, vitreous haemorrhage is not serious, as the blood is eventually taken up again (reabsorbed).  This can take weeks or even months; eventually, however, the vision clears. However,  it is a sign that the retina at the back of the eye is not healthy, and once the blood has cleared, treatment is likely to be needed to prevent it from happening again. Some patients with severe bleeds are offered a procedure which removes the cloudy vitreous and replaces it with saline. The procedure is called a vitrectomy.

Vitreous haemorrhage is most often a consequence of diabetes, where control has not been good and leaky blood vessels have developed inside the eye. Most patients with diabetes in the UK have regular eye monitoring in an effort to prevent this and other conditions occurring. Injury can also cause the eye to bleed in this way.

If you have a vitreous haemorrhage then first and foremost, don't panic, things will improve. To start with, you need to rest for a day or two, sitting upright in a chair during the day, and sleeping with extra pillows to raise your head. This will minimise further bleeding and start to persuade the blood cells to settle to the bottom of the eye and allow you to see a little. It is also important not to lift anything really heavy until you have been advised it is safe, as lifting can increase the pressure in the small blood vessels in the eye and if they remain fragile, they may bleed again..

Giant cell arteritis

This condition is generally only seen in patients over 50 years of age, and usually over 70. It is caused by inflammation of medium-sized blood vessels in the head and neck. When this affects the temporal artery, which supplies the optic nerve with nutrients, the artery can become blocked, and the nerve stops working.

The cause of giant cell arteritis (GCA) is unknown. Often the first sign is pain on chewing, or headache concentrated in the temple. Often the artery is tender to touch and combing hair may be painful. If you see your doctor before vision is lost then the condition can be treated, usually with steroids, and vision is usually saved, so it is important to be aware that soreness of the temples on combing the hair or touching, in combination with a headache, needs a doctor's review.


Migraine can cause a temporary loss of vision - usually patients experience a one-sided area of distorted or absent vision which affects both eyes on the same side. Visual symptoms in migraine do not usually last more than an hour. Patients may see wavy lines or blurred colours, and one-sided headache may follow the visual symptoms. Most patients who experience this will have had migraines before, as migraine is a recurrent condition.

Migraine is, obvously, painful. However the visual loss of migraine occurs before the headache begins. By the time the headache appears it has settled.


It is quite uncommon for stroke to cause blindness, as strokes do not commonly affect the part of the brain with which we see. However, if the back of the brain is affected by a stroke (which is a blood clot in the brain) then temporary or permanent loss of vision may occur. The same symptoms can also follow severe head injury if the back of the brain is damaged.

Gradual visual loss


A pterygium is a raised, yellowish, scar on the white part of the eye (the sclera), which can grow and occasionally spread over the clear window of the eye (the cornea), obstructing vision. Technically, therefore, it blocks vision rather than causing vision loss. It is painless and slow-growing (although when large it can cause irritation and dryness) and it usually requires surgery to correct it. Pterygium occurs as a reaction by the eyes to being exposed to hostile conditions of wind, dryness and sunshine (solar radiation).


A cataract is a clouding of the lens of the eye. Vision becomes blurred, often misty. Early or slight cataracts may not cause symptoms, and they generally get worse only slowly. Gradually, if they become more severe, you may be dazzled by lights, such as car headlamps, and colour vision may become washed out or faded.

The most common type of cataract is an age-related cataract. Cataracts can also result from diabetes, from using steroids (especially lots of steroid drops in the eye), and from injury to the eye.

Treatment is surgery to replace the cloudy lens with a clear plastic one - this should really be done as soon as eyesight interferes with daily life. Most people notice an instant improvement in sight after cataract surgery, although complete healing may take several months. Patients may still need glasses for reading.

Refractive error

Refractive error causes blurring, rather than loss of vision. This type of visual loss is very common, and it occurs in both children and adults. It is due to error in the optical power or focusing of the eye. It includes long-sightedness (when distance vision tends to be preserved but near focus is blurred), short-sightedness (the opposite!) and astigmatism (when a distortion in the shape of the surface of the eye distorts the vision). When the flexibility of the lens declines due to age, leading to a need for spectacles for near vision (reading), the condition is known as presbyopia.

Severe refractive errors can mean patients lack useful vision unless corrected with specacles or contact lenses. Some refractive errors can be corrected with laser treatment to the front of the eye.


Acute glaucoma causes sudden painful loss of vision. Chronic glaucoma, which is much more common, is different - it is silent and symptomless until vision is damaged. Chronic glaucoma results from gradual increase in the fluid pressure in the eye, and is often inherited.

Chronic glaucoma causes gradual but worsening damage to the optic nerve and a gradual loss of vision that occurs a bit at a time. Patients may notice very little at first, as central vision is not affected at first. By the time central vision is lost it is too late to improve it. Opticians perform regular eye pressure checks to look for glaucoma in people over 40 years of age, particularly those with affected relatives. Where glaucoma is detected, patients are put on drops for life. The aim of these drops is to lower the pressure in the eyes. Oddly enough a side-effect of one of the more popular medications is to make the lashes grow longer and the pupils darken. However they are not always well tolerated, and can cause itching and soreness of the eyes.

Macular degeneration

The macula is the spot on the back of the eye where central vision is made - that is, the place where you see the things that you look at directly. Macular degeneration (MD) occurs when this area of the retina degenerates and loses function. This results in gradual loss of central vision, although edge (peripheral) vision is not lost.

MD is the most common cause of blindness in the UK. It is caused by hardening of the arteries which nourish the retina, and it varies in severity. If central vision is completely lost, reading becomes impossible, but in milder cases only visual distortion results.

Most MD progresses only very slowly, and whilst the loss of central vision is disabling, peripheral vision will remain. However, there is a form of MD called wet MD which can progress rapidly. Recently, new medicines have been developed which can improve or even save vision in wet MD.

If you are affected by MD, you should be offered referral to a low vision aid clinic for help and advice, as using peripheral vision to see is a skill you can work on. Tips include using a halogen light, shining light directly on your reading material and using hand-held magnifiers and large-print books.

Diabetic retinopathy

This is damage to the retina caused by the complications of diabetes, particularly where the diabetes has been present for more than ten years, and particularly where control has been less good. Most patients who have had diabetes for more than ten years have some degree of diabetic retinopathy but the majority are mild. In the UK people with diabetes are monitored each year for signs of retinal damage. It is treated when it arises, with the aim of preventing the retinal bleeding and swelling that can lead to visual loss.

The condition often has no early warning signs unless vitreous haemorrhage occurs. Once the retina is badly damaged the visual loss cannot be reversed.

Rarer cause of visual loss

There are many rarer causes of visual loss, some caused by infections (such as fungi), inflammation (such as sarcoidosis) or damage to the optic nerve by drugs or chemicals including meths (methanol). Severe thyroid eye disease related to hyperthyroidism can affect vision through pressure on the optic nerve, and there are also a number of inherited rare causes of gradual visual loss including retinitis pigmentosa and albinism.

Brain or eye tumour

Brain or eye tumours are rarely the cause of loss of vision. Gradual loss of vision can be a symptom of a growing tumour - but it is important to keep a sense of proportion, and remember: gradual loss of vision is very common but brain and eye tumours are very, very rarely the cause.


The eye is a fantastic organ. It is a clever magnifying device that takes light and makes an image on a light-sensitive membrane which is then sent to the brain. essentially, the eye is a camera, the lens is the film (we are talking about old-fashioned cameras here!), and what happens beyond that is to do with the developing. Any interruption in the process - any damage to the component parts or blockage to the route of light - can affect vision. Visual loss is always taken seriously - it is frightening and it requires diagnosis - but it is rarely sinister in cause. The earlier you have it checked out by a doctor or optician, the greater the chance that something can be done.