The white ring or crescent which tends to form at the edge of the CORNEA with age. It is uncommon in the young, when it may be associated with high levels of blood lipids (see LIPID).
See under ERRORS OF REFRACTION.
A chronic inflammation of the lid margins. SEBORRHOEA and STAPHYLOCOCCAL infection are likely contributors. The eyes are intermittently red, sore and gritty over months or years. Treatment is difficult and includes measures to reduce debris on the lid margins. Intermittent courses of topical antibiotics, steroids or systemic antibiotics may help the sufferer.
Involuntary closure of the eye. This may accompany irritation, but may also occur without an apparent cause. Treatment involves removing the source of irritation, if present. Severe and persistent cases may respond to injection of Botulinum toxin into the orbicularis muscle.
Any opacity in the lens of the eye, from the smallest spot to total opaqueness. Cataracts are the most important cause of blindness worldwide. Their prevalence is age-related: 65 per cent of individuals in their sixth decade have some degree of lens opacity, while all those over 80 are affected. The extent of visual impairment depends on the nature of the cataracts. Early symptoms include difficulty in recognising faces and problems watching television or driving, especially at night. If only one eye is developing a cataract, it may be some time before the person notices it, though reading may be affected. Some people with cataracts become short-sighted, which in older people may paradoxically ‘improve’ their ability to read. If a bright light is shone on the eye, the lens may appear brown or, in advanced cataracts, white (see diagram above).
People with DIABETES, UVEITIS and those with a history of injury to the eye can also develop the disorder. Prolonged STEROID treatment can result in cataracts. Children may develop cataracts, and for them the condition is much more serious, since vision may be irreversibly impaired because development of the brain's ability to interpret visual signals is hindered. One of the physical signs which doctors look for when they suspect cataract in adults as well as in children is the ‘red reflex’, seen when looking at the eye through an OPHTHALMOSCOPE.
Cataract: the opaque lens of any eye with cataract (left) is replaced with an implanted artificial lens (right).
The treatment for established cataracts is surgery and the decision when to operate depends mainly on how the cataract(s) affect(s) the patient's vision. Most patients with a vision of 6/18 (6/10 is the minimum standard for driving) or worse in both eyes should benefit from surgery, though elderly people may tolerate visual acuity of 6/18 or worse. Younger people with a cataract will have more demanding visual requirements and so may opt for an ‘earlier’ operation. Cataract surgery in developed countries is usually done under local anaesthetic and uses the ‘phacoemulsification’ method. A small hole is made in the anterior capsule of the lens after which the hard lens nucleus is liquefied ultrasonically. A replacement lens is inserted into the empty lens bag (see diagram). Patients usually return to their normal activities within a few days of the operation.
A firm lump in the eyelid relating to a blocked MEIBOMIAN gland, felt deep within the lid. Treatment is not always necessary since some get better spontaneously. There can be associated infection when the lid becomes red and painful requiring antibiotic treatment. If troublesome, the chalazion can be incised under local anaesthetic.
Inflammation of the conjunctiva. Typically the eye is red, itchy, sticky and gritty but is not usually painful and not always red. It can occasionally be painful, particularly if there is an associated keratitis (see below) – for example, adenovirus infection, herpetic infection.
The cause can be infective (bacteria, viruses or CHLAMYDIA), chemical (e.g. acids, alkalis) or allergic (e.g. in hay-fever). Conjunctivitis may also be caused by contact lenses, preservatives or other constituents of eye drops or with other illnesses – for example, upper-respiratory-tract infection, Stevens-Johnson syndrome (see ERYTHEMA MULTIFORME) or REITER'S SYNDROME. The treatment depends on the cause.
Inflammation of the lacrimal sac. This may present acutely as a red, painful swelling between the nose and the lower lid. An abscess may form which points through the skin and which may need to be drained by incision. Antibiotics may be necessary. Chronic dacryocystitis may occur with recurrent discharge from the openings of the tear ducts and recurrent swelling of the lacrimal sac. Obstruction of the tear duct is accompanied by watering of the eye. If the symptoms are troublesome, the patient's tear passageways need to be dilated or surgically reconstructed.
The lid margin – usually of the lower lid – is everted (folded outwards). It is most commonly associated with ageing, when the tissues of the lid become lax. It can also be caused by shortening of the skin of the lids such as happens with scarring or mechanical factors – for example, a tumour pulling the skin of the lower lid downwards. Ectropion tends to cause watering and an unsightly appearance. The treatment is surgical.
The lid margin – usually of the lower lid – is inverted (folded inwards). It is most commonly associated with ageing, when the tissues of the lid become lax. It can also be caused by shortening of the inner surfaces of the lids, due, for example, to TRACHOMA or chemical burns. The inwardly directed lashes cause irritation and can abrade the cornea. The treatment is surgical.
Inflammation of the EPISCLERA, usually of unknown cause. It may respond to NON-STEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS) or topical CORTICOSTEROIDS.
(Ametropia.) These will occur when the focusing power of the lens and cornea does not match the length of the eye, so that rays of light parallel to the visual axis are not focused at the fovea centralis (see EYE). There are three types of refractive error:
or long-sightedness. The refractive power of the eye is too weak, or the eye is too short so that rays of light are brought to a focus at a point behind the retina. Long-sighted people can see well in the distance but generally require glasses with convex lenses for reading. Uncorrected long sight can lead to headaches and intermittent blurring of vision following prolonged close work (i.e. eye strain). The eye becomes gradually long-sighted with age, resulting in many people needing reading glasses in later life: this normal process is known as presbyopia. A particular form of long-sightedness occurs after cataract extraction (see above).
(Short sight or near sight.) Rays of light are brought to a focus in front of the retina because the refractive power of the eye is too great or the eye is too short. Short-sighted people can see close-to but need spectacles with concave lenses in order to see in the distance.
The refractive power of the eye is not the same in each meridian. Some rays of light may be focused in front of the retina while others are focused on or behind the retina. Astigmatism can accompany hypermetropia or myopia. It may be corrected by cylindrical lenses: these consist of a slice from the side of a cylinder (i.e. curved in one meridian and flat in the meridian at right-angles to it).
Inflammation of the cornea in response to a variety of insults – viral, bacterial, chemical, radiation, or mechanical trauma. The eye is usually red and painful, and light causes discomfort or pain (photophobia). Treatment is directed at the cause.
Involuntary rhythmic oscillation of one or both pupils. There are several causes including nervous disorders, vestibular disorders, eye disorders and certain drugs including alcohol.
Inflammation of the eye, especially the conjunctiva (see conjunctivitis above). Ophthalmia neonatorum is a type of conjunctivitis that occurs in newborn babies who catch the disease when passing through an infected birth canal during their mother's labour (see PREGNANCY AND LABOUR). CHLAMYDIA and GONORRHOEA are the two most common infections. Treatment is effective with antibiotics: untreated, the infection may cause permanent eye damage.
A benign degenerative change in the connective tissue at the nasal or temporal limbus (see EYE), visible as a small, flattened, yellow-white lump adjacent to the cornea.
Overgrowth of the conjunctival tissues at the limbus onto the cornea (see EYE). This usually occurs on the nasal side and is associated with exposure to sunlight. The pterygium is surgically removed for cosmetic reasons or if it is thought to be advancing towards the visual axis.
Drooping of the upper lid which may occur because of a defect in the muscles which raise the lid (levator complex), sometimes the result of ageing or trauma. Other causes include HORNER'S SYNDROME, third cranial nerve PALSY, MYASTHENIA GRAVIS, and DYSTROPHIA MYOTONICA. The treatment for a severely drooping lid is surgical, but other measures can be used to prop up the lid with varying degrees of success.
The retina can be damaged by disease that affects the retina alone, or by diseases affecting the whole body.
Retinopathy is a term used to denote an abnormality of the retina without specifying a cause. Some retinal disorders are discussed below.
Retinal disease occurring in patients with DIABETES MELLITUS. It is the commonest cause of blind registration in Great Britain of people between the ages of 20 and 65. Diabetic retinopathy can be divided into several types. The two main causes of blindness are from growth of new blood vessels into the retina, with resultant complications, and from ‘water logging’ (oedema) of the macula. Treatment is by maintaining rigid control of blood-sugar levels, combined with laser treatment for certain forms of the disease – in particular to destroy new blood vessels.
Retinal disease secondary to the development of high blood pressure. Treatment involves control of the blood pressure (see HYPERTENSION).
People with SICKLE CELL DISEASE can develop a number of retinal problems including new blood vessels from the retina.
Previously called retrolental fibroplasia (RLF), this is a disorder affecting low-birth-weight premature babies exposed to oxygen. New blood vessels develop which cause extensive traction on the retina with resultant retinal detachment and poor vision.
These result in damage to those areas of retina supplied by the affected blood vessel: the blood vessels become blocked. If the peripheral retina is damaged the patient may be completely symptom-free, although areas of blindness may be detected on examination of field of vision. If the macula is involved, visual loss may be sudden, profound and permanent. There is no effective treatment once visual loss has occurred.
This is the leading cause of poor sight in the elderly in the western world but does not always lead to complete blindness. The average age of onset is 65 years. Patients initially notice a disturbance of their vision, which gradually progresses over months or years. They lose the ability to recognise fine detail; for example, they cannot read fine print, sew, or recognise people's faces, and colours fade away. They always retain the ability to recognise large objects such as doors and chairs, and are therefore able to get around reasonably well. There are two types of the condition – ‘wet’ and ‘dry.’ The wet form involves new blood vessels growing behind the retina which may result in rapid, rather than gradual visual loss. Sometimes only one eye is affected. Genes, the effect of sunlight and smoking all have a role in its cause. There is no effective treatment for ‘dry AMD’. Wet AMD can be treated with photodynamic therapy; this involves infusing a drug into the bloodstream and then directing a laser onto the retina. An effective treatment for wet AMD is the use of anti-VEGF drugs, which, when injected directly into the eye can stop new blood vessels growing. Treatment is repeated every few weeks.
A group of rare, inherited diseases characterised by the development of night blindness and tunnel vision. Symptoms start in childhood and are progressive. Many patients retain good visual acuity, although their peripheral vision is limited. One of the characteristic findings on examination is collections of pigment in the retina which have a characteristic shape and are therefore known as ‘bone spicules’. There is no effective treatment.
usually occurs due to the development of a hole in the retina. Holes can occur as a result of degeneration of the retina, traction on the retina by the vitreous, or injury. Fluid from the vitreous passes through the hole causing a split within the retina; the inner part of the retina becomes detached from the outer part, the latter remaining in contact with the choroid. Detached retina loses its ability to detect light, with consequent impairment of vision. Retinal detachments are more common in the short-sighted, in the elderly or following cataract extraction. Symptoms include spots before the eyes (floaters), flashing lights and a shadow over the eye with progressive loss of vision. Treatment by laser is very effective if caught early, at the stage when a hole has developed in the retina but before the retina has become detached. The edges of the hole can be ‘spot welded’ to the underlying choroid. Once a detachment has occurred, laser therapy cannot be used; the retina has to be repositioned. This is usually done by indenting the wall of the eye from the outside to meet the retina, then making the retina stick to the wall of the eye by inducing inflammation in the wall (by freezing it). The outcome of surgery depends largely on the extent of the detachment and its duration. Complicated forms of detachment can occur due to diabetic eye disease, injury or tumour. Each requires a specialised form of treatment.
Inflammation of the sclera (see EYE). The affected eye is usually red and painful. Scleritis can lead to thinning and even perforation of the sclera, sometimes with little sign of inflammation. Posterior scleritis in particular may cause impaired vision and require emergency treatment. There is often no apparent cause, but there are some associated conditions – for example, RHEUMATOID ARTHRITIS, GOUT, and an autoimmune disease affecting the nasal passages and lungs called Wegener's granulomatosis. Treatment depends on severity but may involve NON-STEROIDAL ANTI-INFLAMMATORY DRUGS, topical CORTICOSTEROIDS or systemic IMMUNOSUPPRESSIVE drugs.
Infection of a lash follicle. This presents as a painful small red lump at the lid margin. It often resolves spontaneously but may require antibiotic treatment if it persists or recurs.
Haemorrhage between the conjunctiva and the underlying episclera. It appears as a painless red blotch on the white of the eye. There is usually no apparent cause and it gets better without treatment.
Inward misdirection of the lashes. Trichiasis occurs due to inflammation of or trauma to the lid margin. Treatment involves removal of the patient's lashes. Regrowth may be prevented by electrolysis, by CRYOTHERAPY to the lid margin, or by surgery.
For the subject of artificial eyes, see under PROSTHESES; GLAUCOMA, SQUINT and UVEITIS.