BMA Concise Guide to Medicine & Drugs

EYES AND EARS

The eyes and ears are the two sense organs that provide us with the most information about the world around us. The eye is the organ of vision that converts light into nerve signals, which are transmitted to the brain for interpretation into images. The ear not only provides the means by which sound is detected and communicated to the brain, but it also contains the organ of balance that tells the brain about the position and movement of the body. It is divided into three parts: the outer, middle, and inner ear.

WHAT CAN GO WRONG

The most common eye and ear disorders are infection and inflammation (sometimes caused by allergy). Many parts of the eye may be affected, notably the conjunctiva (the membrane that covers the front of the eye and lines the eyelids) and the iris. The middle and outer ear are more commonly affected by infection than the inner ear.

The eye may also be damaged by glaucoma, a disorder in which pressure of fluid within the eye builds up and may eventually threaten vision. Eye problems such as retinopathy (disease of the retina) or cataracts (clouding of the lens) may occur as a result of diabetes or for other reasons, but both conditions are now treatable. Disorders for which no drug treatment is appropriate are beyond the scope of this guide.

Other disorders affecting the ear include build-up of wax (cerumen) in the outer ear canal and disturbances to the balance mechanism within the ear (vertigo and Ménière’s disease, see Anti-emetics).

WHY DRUGS ARE USED

Doctors usually prescribe antibiotics to clear ear and eye infections. These may be given by mouth or topically. Topical eye and ear preparations may contain a corticosteroid to reduce inflammation. When inflammation has been caused by allergy, antihistamines may also be taken. Decongestant drugs are often prescribed to help clear the eustachian tube in middle-ear infections.

Various drugs are used to reduce fluid pressure in glaucoma. These include diuretics, beta blockers, and miotics (to narrow the pupil). In other cases, the pupil may need to be widened by mydriatic drugs. (See also Drugs affecting the pupil.)

MAJOR DRUG GROUPS

· Drugs for glaucoma

· Drugs affecting the pupil

· Drugs for ear disorders

Drugs for glaucoma

Glaucoma is the name given to a group of conditions in which the pressure in the eye builds up to an abnormally high level. This compresses the blood vessels that supply the nerve connecting the eye to the brain (optic nerve) and may result in irreversible nerve damage and permanent loss of vision.

In the most common type, called chronic (or open-angle) glaucoma, reduced drainage of fluid from the eye causes pressure inside the eye to build up slowly. Progressive reduction in the peripheral field of vision may take months or years to be noticed. Acute (or closed-angle) glaucoma occurs when drainage of fluid is suddenly blocked by the iris. Fluid pressure usually builds up quite suddenly, blurring vision in the affected eye. The eye becomes red and painful, and a headache and sometimes vomiting also occur. The main attack is often preceded by milder warning attacks, such as seeing haloes around lights in the previous weeks or months. Elderly farsighted people are particularly at risk of developing acute glaucoma. The angle may also narrow suddenly following injury or after taking certain drugs such as anticholinergic drugs. Closed-angle glaucoma may develop more slowly (chronic closed-angle glaucoma).

Drugs are used in the treatment of both types of glaucoma. These include miotics (see Drugs affecting the pupil), beta blockers, and the diuretics, carbonic anhydrase inhibitors and osmotics.

WHY THEY ARE USED

Chronic (open-angle) glaucoma In this form of glaucoma, drugs are used to reduce pressure inside the eye. These drugs will prevent further deterioration of vision, but they cannot restore damage that has already been sustained and may therefore be required lifelong. In most patients, treatment is begun with eye drops containing a beta blocker to reduce fluid production inside the eye. Miotic eye drops to constrict the pupil and improve fluid drainage may be given. The prostaglandin analogues, such as latanoprost, are also used to increase fluid outflow. If none of these drugs is effective, dipivefrine, apraclonidine, or brimonidine may be tried to reduce secretion and help outflow. Sometimes a carbonic anhydrase inhibitor such as acetazolamide or dorzolamide may be given to reduce fluid production. Laser treatment and surgery may also be used to improve fluid drainage from the eye.

Acute (closed-angle) glaucoma In acute glaucoma immediate medical treatment is required in order to prevent total loss of vision. Drugs are used initially to bring down the pressure within the eye. Laser treatment or surgery is then carried out to prevent a recurrence of the problem so that long-term drug treatment is seldom required.

Acetazolamide is often the first drug administered when the condition is diagnosed. It may be injected into a vein for rapid effect and thereafter administered by mouth. Frequent applications of eye drops containing pilocarpine or carbachol are given. An osmotic diuretic such as mannitol may be administered. This draws fluid out of all body tissues, including the eye, and reduces pressure within the eye.

HOW THEY WORK

Drugs for glaucoma act in various ways to reduce fluid pressure in the eye. Miotics improve drainage of fluid out of the eye. In chronic glaucoma, this is achieved by increasing the outflow of aqueous humour via the drainage channel called the trabecular meshwork. In acute glaucoma, the pupil-constricting effect of miotics pulls the iris away from the drainage channel, allowing the aqueous humour to flow out. Prostaglandin analogues act by increasing fluid flow from the eye. Beta blockers and carbonic anhydrase inhibitors act on the fluid-producing cells inside the eye to reduce the production of aqueous humour. Sympathomimetics such as brimonidine and apraclonidine are also thought to act partly in this way and partly by improving fluid drainage.

HOW THEY AFFECT YOU

Drugs for acute glaucoma relieve pain and other symptoms within a few hours of their being used. The benefits of treatment in chronic glaucoma, however, may not be immediately apparent since treatment is only able to halt a further deterioration of vision.

People receiving miotic eye drops are likely to notice darkening of vision and difficulty in seeing in the dark. Increased shortsightedness may be noticeable. Some miotics also cause irritation and redness of the eyes.

Beta blocker eye drops have few day-to-day side effects but carry risks for a few people. Oral acetazolamide usually causes an increase in frequency of urination and thirst. Nausea and a pins-and-needles sensation are also common.

RISKS AND SPECIAL PRECAUTIONS

Miotics can cause alteration in vision. Beta blockers are absorbed into the body and can affect the lungs, heart, and circulation. As a result, a cardioselective beta blocker, such as betaxolol, is prescribed with caution to people with asthma or certain circulatory disorders and, in some cases, such drugs are withheld altogether. The amount of the drug absorbed into the body can be reduced by pressing on the lacrimal (tear) duct in the corner of the eye while applying the number of eye drops prescribed by your doctor. Acetazolamide may cause troublesome adverse effects, including tingling of the hands and feet, the formation of kidney stones, and, rarely, kidney damage. People with existing kidney problems are not usually given this drug.

COMMON DRUGS

Miotics Carbachol, Pilocarpine

Carbonic anhydrase inhibitors Acetazolamide, Brinzolamide, Dorzolamide

Prostaglandin analogues Bimatoprost, Latanoprost, Travoprost

Beta blockers Betaxolol, Carteolol, Levobunolol, Metipranolol, Timolol

Sympathomimetics Apraclonidine, Brimonidine, Dipivefrine

Drugs affecting the pupil

The pupil of the eye is the circular opening in the centre of the iris (the coloured part of the eye) through which light enters. It continually changes in size to adjust to variations in the intensity of light; in bright light it becomes quite small (constricts), but in dim light the pupil enlarges (dilates).

Eye drops containing drugs that act on the pupil are widely used by specialists. There are two categories: mydriatics, which dilate the pupil, and miotics, which constrict it.

WHY THEY ARE USED

Mydriatics are most often used to allow the doctor to view the inside of the eye – particularly the retina, the optic nerve head, and the blood vessels that supply the retina. Many of these drugs cause a temporary paralysis of the eye’s focusing mechanism, a state called cycloplegia. Cycloplegia is sometimes induced to help determine the presence of any focusing errors, especially in babies and young children. By producing cycloplegia, it is possible to determine the precise optical prescription required for a small child, especially in the case of a squint.

Dilation of the pupil is part of the treatment for uveitis, an inflammatory disease of the iris and focusing muscle. In uveitis, the inflamed iris may stick to the lens, severely damaging the eye. This complication can be prevented by early dilation of the pupil so that the iris is no longer in contact with the lens.

Constriction of the pupil with miotic drugs is often required in the treatment of glaucoma. Miotics can also be used to restore the pupil to a normal size after dilation is induced by mydriatics.

HOW THEY WORK

The size of the pupil is controlled by two separate sets of muscles in the iris, the circular muscle and the radial muscle. The two sets of muscles are governed by separate branches of the autonomic nervous system: the radial muscle is controlled by the sympathetic nervous system, and the circular muscle is controlled by the parasympathetic nervous system.

Individual mydriatic and miotic drugs affect different branches of the autonomic nervous system, and cause the pupil to dilate or contract, depending on the type of drug.

HOW THEY AFFECT YOU

Mydriatic drugs – especially the long-acting types – impair the ability to focus the eye(s) for several hours or even days after use. This interferes particularly with close activities such as reading. Bright light may cause discomfort. Miotics often interfere with night vision and may cause temporary short sight.

Normally, these eye drops produce few serious adverse effects. Sympathomimetic mydriatics may raise blood pressure and are used with caution in people with hypertension or heart disease. Miotics may irritate the eyes, but rarely cause generalized effects.

ARTIFICIAL TEAR PREPARATIONS

Tears are continually produced to keep the front of the eye covered with a thin, moist film. This is essential for clear vision and for keeping the front of the eye free from dirt and other irritants. In some conditions, known collectively as dry eye syndromes (for example, Sjögren’s syndrome), inadequate tear production may make the eyes feel dry and sore. Sore eyes can also occur in disorders where the eyelids do not close properly, causing the eye to become dry.

Why they are used Since prolonged deficiency of natural tears can damage the cornea, regular application of artificial tears in the form of eye drops is recommended for all of the conditions described here. Artificial tears may also be used to provide temporary relief from any feeling of discomfort and dryness in the eye caused by irritants or exposure to wind or sun, or following the initial wearing of contact lenses.

Although artificial tears are non-irritating, they often contain a preservative (such as thiomersal or benzalkonium chloride) that may cause irritation. This risk of irritation is increased for wearers of soft contact lenses, who should ask their optician for advice before using any type of eye drops.

COMMON DRUGS

Sympathomimetic mydriatics Phenylephrine

Miotics Carbachol, Pilocarpine

Anticholinergic mydriatics Atropine, Cyclopentolate, Homatropine, Tropicamide

Drugs for ear disorders

Inflammation and infection of the outer and middle ear are the most common ear disorders treated with drugs. Drug treatment for Ménière’s disease, which affects the inner ear, is described under Anti-emetics.

The type of drug treatment given for ear inflammation depends on the cause of the trouble and the site affected.

INFLAMMATION OF THE OUTER EAR

Inflammation of the external ear canal (otitis externa) can be caused by eczema or by a bacterial or fungal infection. The risk of inflammation is increased by swimming in dirty water, an accumulation of wax in the ear, or scratching or poking too frequently at the ear.

Symptoms vary, but in many cases there is itching, pain (which may be severe if there is a boil in the ear canal), tenderness, and possibly some loss of hearing. If the ear is infected there will probably be a discharge.

Drug treatment A corticosteroid in the form of ear drops may be used to treat inflammation of the outer ear when there is no infection. Aluminium acetate solution, as drops or applied on a piece of gauze, may also be used. Relief is usually obtained within a day or two. Prolonged use of corticosteroids is not advisable because they may reduce the ear’s resistance to infection.

If there is both inflammation and infection, your doctor may prescribe ear drops containing an antibiotic combined with a corticosteroid to relieve the inflammation. Usually, a combination of antibiotics is prescribed to make the treatment effective against a wide range of bacteria. Commonly used antibiotics include framycetin, neomycin, and polymyxin B. These are not used if the eardrum is perforated and are not usually applied for long periods because they can irritate the skin that lines the ear canal.

Sometimes an antibiotic given as drops is not effective, and another type of antibiotic may also have to be taken by mouth.

INFECTION OF THE MIDDLE EAR

Infection of the middle ear (otitis media) often causes severe pain and hearing loss. It is particularly common in young children in whom infecting organisms are able to spread easily into the middle ear from the nose or throat via the eustachian tube.

Viral infections of the middle ear usually cure themselves and are less serious than those caused by bacteria, which are treated with antibiotics given by mouth or injection. Bacterial infections often cause the eustachian tube to swell and become blocked. When a blockage occurs, pus builds up in themiddle ear and puts pressure on the eardrum, which may perforate as a result.

Drug treatment Doctors usually prescribe a decongestant or antihistamine to reduce swelling in the eustachian tube, thus allowing the pus to drain out of the middle ear. Usually, an antibiotic is also given by mouth to clear the infection.

Although antibiotics are not effective against viral infections, it is often difficult to distinguish between a viral and a bacterial infection of the middle ear, so your doctor may prescribe an antibiotic as a precautionary measure. Paracetamol, an analgesic, may be given to relieve pain.

COMMON DRUGS

Antibiotic and antibacterial ear drops Chloramphenicol, Clioquinol, Clotrimazole, Framycetin, Gentamicin, Neomycin

Decongestants Ephedrine, Oxymetazoline, Xylometazoline

Corticosteroids Betamethasone, Dexamethasone, Flumetasone, Hydrocortisone, Prednisolone, Triamcinolone

Other drugs Aluminium acetate, Antihistamines, Choline salicylate