The special senses

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Chapter 21 The special senses

Disorders of the ear, nose and throat

The Ear

Anatomy and physiology

The ear can be divided into three parts: outer, middle and inner (Fig. 21.1).

The outer ear has a skin-lined tube 2.5 cm long leading down to the tympanic membrane (the ear drum). Its outer third is cartilaginous and contains hair, sebaceous and ceruminous glands, but the walls of the inner two-thirds are bony. The outer ear is self-cleaning as the skin is migratory and there are no indications to use cotton wool buds. Wax should only be seen in the outer third.

The middle ear is an air-containing cavity derived from the branchial clefts. It communicates with the mastoid air cells superiorly, and the Eustachian tube connects it to the nasopharynx medially. The Eustachian tube ventilates the middle ear and maintains equal air pressure across the tympanic membrane. It is normally closed but opens via the action of the palatal muscles to allow air entry when swallowing or yawning. A defect in this mechanism, such as with a cleft palate, will prevent air entering the middle ear cleft which may then fill with fluid. Lying within the middle ear cavity are the three ossicles (malleus, incus and stapes) that transmit sound from the tympanic membrane to the inner ear. On the medial wall of the cavity is the horizontal segment of the facial nerve, which can be damaged during surgery or by direct extension of infection in the middle ear.

The inner ear contains the cochlea for hearing and the vestibule and semicircular canals for balance. There is a semicircular canal arranged in each body plane and these are stimulated by rotatory movement. The facial, cochlear and vestibular nerves emerge from the inner ear and run through the internal acoustic meatus to the brainstem (see Fig. 22.7, p. 1076).

Common disorders

The discharging ear (otorrhoea)

Discharge from the ear is usually due to infection of the outer or middle ear.

Hearing loss

Deafness can be conductive or sensorineural and these can be differentiated at the bedside by the Rinne and the Weber tests (Box 21.1) or with pure-tone audiometry. Conductive hearing loss has many causes (Table 21.1) but wax is the commonest.

Table 21.1 Deafness

Conductive Sensorineural

External meatus

Congenital

WaxForeign bodyOtitis externaChronic suppurationDrum

Pendred’s syndrome (see p. 962)

Long QT syndrome

Björnstad’s syndrome (pili torti)

End organ

Advancing ageOccupational acoustic traumaMénière’s diseaseDrugs (e.g. gentamicin, furosemide)

Perforation/trauma

Middle ear

Otosclerosis
Ossicular bone problems
Suppuration (otitis media)

Eighth nerve lesions

Acoustic neuroma

 

Cranial trauma

 

Inflammatory lesions:

 

Tuberculous meningitis

 

Sarcoidosis

 

Neurosyphilis

 

Carcinomatous meningitis

 

Brainstem lesions (rare)

 

Multiple sclerosis

 

Infarction

Acoustic neuroma

This is a slow-growing benign schwannoma of the vestibular nerve (see p. 1076) which can present with progressive sensorineural hearing loss. Any patient with an asymmetric sensorineural hearing loss or sudden sensorineural hearing loss should be investigated, e.g. with an MRI scan.

Vertigo

Vertigo is usually rotatory when it arises from the ear. The presence of otalgia, otorrhoea, tinnitus or hearing loss suggests an otologic aetiology. Vestibular causes can be classified according to the duration of the vertigo. Common causes are summarized below.

Benign paroxysmal positional vertigo (BPPV)

BPPV is thought to be due to loose otoliths in the semicircular canals, commonly the posterior canal. Positional vertigo is precipitated by head movements, usually to a particular position, and often occurs when turning in bed or on sitting up. The onset is typically sudden and distressing. The vertigo lasts seconds or minutes and the phenomenon becomes less severe on repeated movements (fatigue). There is no serious underlying cause but it sometimes follows vestibular neuronitis (see p. 1079), head injury or ear infection.

The nose

Anatomy and physiology (Fig. 21.4)

The function of the nose is to facilitate smell and respiration:

The external portion of the nose consists of two nasal bones attached to the rest of the facial skeleton and to the upper and lower lateral cartilages. The internal nose is divided by a midline septum that comprises both cartilage and bone. This divides the internal nose in two, from the external nostril to the posterior choanae. The posterior choanae are in continuity with the nasopharynx posteriorly. The paranasal sinuses open into the lateral wall of the nose and are a system of aerated chambers within the facial skeleton.

The blood supply of the nose is derived from branches of both the internal and external carotid arteries. The internal carotid artery supplies the upper nose via the anterior and posterior ethmoidal arteries. The external carotid artery supplies the posterior and inferior portion of the nose via the superior labial artery, greater palatine artery and sphenopalatine artery. On the anterior nasal septum is an area of confluence of these vessels (Little’s area) (Fig. 21.5a).

Common disorders

Epistaxis

Nose bleeds vary in severity from minor to life-threatening. Little’s area (Fig. 21.5a) is a frequent site of nasal haemorrhage. First aid measures should be administered immediately, including external digital compression of the anterior lower portion of the external nose, ice packs and leaning forward. The patient should be asked to avoid swallowing any blood running posteriorly as this causes gastric irritation and then nausea and vomiting.

Not infrequently, small recurrent epistaxes occur and these may require a visit to the emergency clinic for an examination and simple local anaesthetic cautery with a silver nitrate stick. If the bleeding continues profusely then resuscitation in the form of intravenous access, fluid replacement or blood, and oxygen can be administered. If further intervention is necessary, consideration should be given to intranasal cautery of the bleeding vessel, or intranasal packing using a variety of commercially available nasal packs (Fig. 21.5b). In addition to direct treatment of the epistaxis, a cause and appropriate treatment of a cause should be sought (Table 21.2).

Table 21.2 Aetiology of epistaxis

Local

Idiopathic

Trauma – foreign bodies, nose-picking and nasal fractures

Iatrogenic – surgery, intranasal steroids

Neoplasm – nasal, paranasal sinus and nasopharyngeal tumours

General

Anticoagulants

Coagulation disorders

Hypertension

Osler–Weber–Rendu syndrome (familial haemorrhagic telangiectasia)

Nasal obstruction

Nasal obstruction is a symptom and not a diagnosis. It can significantly affect a patient’s quality of life. Causes include:

Sinusitis

Sinusitis is an infection of the paranasal sinuses that either is bacterial (mainly Streptococcus pneumoniae and Haemophilus influenzae) or is occasionally fungal. It is most commonly associated with an upper respiratory tract infection and can occur with asthma. Symptoms include frontal headache, purulent rhinorrhoea, facial pain with tenderness and fever. It can be confused with a variety of other conditions such as migraine, trigeminal neuralgia and cranial arteritis.

The throat

Anatomy and physiology

The throat can be considered as the oral cavity, the pharynx and the larynx (Fig. 21.6). The oral cavity extends from the lips to the tonsils. The pharynx can be divided into three areas:

Lying within the hypopharynx is the larynx. This consists of cartilaginous, ligamentous and muscular tissue with the primary function of protecting the distal airway. The pharynx is innervated from the pharyngeal plexus.

In the larynx, there are two vocal cords which abduct (open) during inspiration and adduct (close) to protect the airway and for voice production (phonation). The main nerve supply of the vocal cords comes from the recurrent laryngeal nerves (branches of the vagus nerve) which arise in the neck, but on the left side passes down around the aortic arch and then ascends in the tracheo-oesophageal groove to the larynx.

Normal vocal cords in phonation vibrate between 90 (male) and 180 (female) times per second, giving the voice its pitch or frequency. A healthy voice requires full closure of the vocal cords with a smooth, regular pattern of vibration, and any pathology that prevents full closure will result in air escaping between the vocal cords during phonation and a ‘breathy’ voice.

Common disorders

Hoarseness (dysphonia)

There are three essential components for voice production: an air source (the lungs); a vibratory source (the vocal cords); and a resonating chamber (the pharynx, the nasal and oral cavities). Although chest and nasal disorders can affect the voice, the majority of hoarseness is due to laryngeal pathology.

Inflammation which increases the ‘mass’ of the vocal cords will cause the vocal cord frequency to fall, giving a much deeper voice. Thus listening to a patient’s voice can often give a diagnosis before the vocal cords are examined.

Stridor

Stridor or noisy breathing can be divided into:

All people with stridor, both paediatric and adult, are potentially at risk of asphyxiation and should be investigated fully. Severe stridor may be an indication for either intubation or a tracheostomy (Table 21.3).

Table 21.3 Indications for tracheostomy

Tonsillitis and pharyngitis

Viral infections of the throat are common and, although many practitioners are under pressure from the patient to give antibiotics, the vast majority are usually self-limiting, settling with bed rest, analgesia and encouraging fluid intake. Fungal infections, usually candidiasis, are uncommon and may indicate an immunocompromised patient or undiagnosed diabetes.

Snoring

Snoring is due to vibration of soft tissue above the level of the larynx. It is a common condition (50% of 50-year-old males will snore to some extent) and can be considered to be related to obstruction of three potential areas: the nose, the palate or/and the hypopharynx (see Fig. 15.26).

The Epworth questionnaire (see Table 15.11) can assist in the discrimination of sleep apnoea from simple snoring. People with a history of habitual, non-positional, heroic (can be heard through a wall) snoring require a full ENT examination and can be investigated by sleep nasendoscopy in which a sedated, snoring patient has a flexible nasendoscope inserted to identify the source of vibration.

Nasal pathology such as polyps can be removed surgically with good results and most patients will benefit from lifestyle changes such as weight loss. Stiffening or shortening the soft palate via surgery, often using a laser, can help for palatal snorers but hypopharyngeal snorers require either a dental prosthesis at night to hold the mandible forward or continuous positive airway pressure (CPAP) via a mask (see p. 818).

Dysphagia

Difficulty in swallowing is a common symptom but can be the presenting feature of carcinoma of the pharynx and therefore requires investigation. Dysphagia (see p. 237) occurs because of any lesion between the throat and stomach. The two conditions described here are the ones usually dealt with by ENT departments. Gastroenterology departments see causes further down the gullet.

A pharyngeal pouch is a herniation of mucosa through the fibres of the inferior pharyngeal constrictor muscle (cricopharyngeus) (Fig. 21.7a). An area of weakness known as Killian’s dehiscence allows a pulsion diverticulum to form. This will collect food, which may regurgitate into the mouth or even down to the lungs at night with secondary pneumonia. Diagnosis is made with a barium swallow and treatment is surgical, either via an external approach through the neck where the pouch is excised or more commonly endoscopically with stapling of the party wall (Fig. 21.7b).

Foreign bodies in the pharynx can be divided into three general categories: soft food bolus, coins (smooth), bones (sharp). Soft food bolus can be initially treated conservatively with muscle relaxants for 24 hours. Impacted coins should be removed at the earliest opportunity but sharp objects require emergency removal to avoid perforation of the muscle wall.

If the patient perceives the foreign body to be to one side, then it should be above the cricopharyngeus and an ENT examination will locate it; common areas are the tonsillar fossae, base of tongue, posterior pharyngeal wall and valleculae. Radiology will identify coins, and it can be a clinical decision to see whether a coin will pass down to the stomach, in which case no further treatment is required as it will exit naturally. Some departments advocate the use of a metal detector to monitor the position of the coin in the patient, who is usually a child or has a mental disorder. Fish can be divided into those with a bony skeleton (teleosts) and those with a cartilaginous skeleton (elasmobranchs), and therefore radiology is useful only in some cases. Radiology can also identify air in the cervical oesophagus indicating a radiolucent foreign body lying distally. A soft tissue lateral neck radiograph is the investigation of choice to delineate some of the features above.

Disorders of the eye

Most of the major and common types of eye disease are covered below. However, diabetic eye disease and hypertensive eye disease are discussed elsewhere.

Applied anatomy and physiology

The average length of the human eye is 24 mm. It is essentially made up of two segments:

It is the cornea and the sclera that give the mechanical strength and shape to the exposed surface of the eye.

The cornea occupies the central aspect of the globe and is one of the most richly innervated tissues in the body. This clear, transparent and avascular structure, measuring 12 mm horizontally and 11 mm vertically, provides 78% of the focusing power of the eye. The eyelids prevent the cornea from drying and becoming an irregular surface by distributing the tear film over the surface of the globe with each blink.

Anatomically the cornea is made up of five layers:

The endothelial cells lining the inner surface of the cornea are responsible for maintaining the clarity of the cornea by continuously pumping fluid out of the tissue. Any factor which alters the function of these cells will result in corneal oedema and cause blurred vision.

The sclera is a white opaque structure covering four-fifths of the globe and is continuous with the cornea at the limbus. The six extraocular muscles responsible for eye movements are attached to the sclera and the optic nerve perforates it posteriorly.

The conjunctiva covers the anterior surface of the sclera. This richly vascularized and innervated mucous membrane stretches from the limbus over the anterior sclera (where it is called the bulbar conjunctiva) and is then reflected onto the undersurface of the upper and lower lids (the tarsal conjunctiva). The area of conjunctival reflection under the lids makes up the upper and lower fornix.

The anterior chamber is the space between the cornea and the iris, and is filled with aqueous humour (Fig. 21.8). This fluid is produced by the ciliary body (2 µL/min) and provides nutrients and oxygen to the avascular cornea. The outflow of aqueous humour is through the trabecular meshwork and canal of Schlemm adjacent to the limbus. Any factor which impedes its outflow will increase the intraocular pressure. The upper range of normal for intraocular pressure is 21 mmHg.

The uveal tract is made up of the iris anteriorly, the ciliary body and the choroid.

The iris is the coloured part of the eye under the transparent cornea. The muscles of the iris diaphragm regulate the size of the pupil, thereby controlling the amount of light entering the eye. The muscles of the ciliary body control the accommodation of the lens and the secretory epithelium produces the aqueous humour (see above). The highly vascular choroid lines the inner aspect of the sclera and upon this lies the retina.

The lens lies immediately posterior to the pupil and anterior to the vitreous humour. It is a transparent biconvex structure and is responsible for 22% of the refractive power of the eye. By changing its shape it can alter its refractive power and help to focus objects at different distances from the eye. By the fourth decade of life this ability to change shape starts to decline and with time the lens starts to become less transparent and cataracts begin to develop.

The vitreous humour fills the cavity between the retina and the lens.

The retina is a multi-layered structure. The metabolically active region of the retina is represented in Figure 21.9. There are two types of photoreceptors in the retina, rods and cones. There are approximately 6 million cones mainly confined to the macula and these are responsible for detailed central vision and colour vision. The peripheral retina has around 125 million rods that are responsible for peripheral vision. The axons of the ganglion cells form the optic nerve (or disc) of the eye (Fig. 21.10).

The blood supply to the eye is via the ophthalmic artery and, in particular, the central retinal artery is responsible for supplying the inner retinal layers. Venous return is through the central retinal and ophthalmic veins. Local lymphatic drainage is to the preauricular and submental nodes.

The sensory innervation of the eye is through the trigeminal (V) nerve. The six extraocular muscles are supplied by different nerves.

The oculomotor (III) nerve also supplies the upper lid and indirectly the pupil (parasympathetic fibres are attached to it). The facial (VII) nerve supplies the orbicularis and other muscles of facial expression.

Refractive errors

The eye projects a sharp and focused image onto the retina. Refractive errors refer to any abnormality in the focusing mechanism of the eye and not to any opacity in the system such as a corneal or retinal scar.

The refraction of light in emmetropic (normal), myopic (short-sighted, negative lenses will correct) and hypermetropic (long-sighted, positive lenses will correct) eyes is shown in Figure 21.11.

Astigmatism is a retractive error of the eye in which there is a different degree of refraction in the different meridians of curvature. It may be myopic in one plane and hypermetropic or emmetropic in the other plane. In this situation the front surface of the eye is more rugby ball shaped than football shaped.

Presbyopia is the term used to describe the normal ageing of the lens and leads to a change in the refractive state of the eye. As the lens ages it becomes less able to alter its curvature and this causes difficulty with near vision, especially reading.

Disorders of the lids

The lids afford protection to the eyes and help to distribute the tear film over the front surface of the globe. Excess tears are drained via the punctae and lacrimal system to the nose (Fig. 21.12). Malposition of the lids, factors which affect blinking or lacrimal drainage, can all cause problems.

Entropion. The lid margin rolls inwards so that the lashes are against the globe (Fig. 21.13a). The lashes act as a foreign body and cause irritation, leading to a red eye which can mimic conjunctivitis. Occasionally the constant rubbing of lashes against the cornea causes an abrasion. The commonest cause is ageing and surgery is usually required.

Ectropion. The lid margin rolls outwards and is not apposed to the globe. As a result the lacrimal puncta is not in the correct anatomical position to drain tears and patients usually complain of a watery eye. Underlying factors include age, VII nerve palsy and cicatricial skin conditions. Surgery is usually required.

Dacryocystitis. Patients who have inflammation of the lacrimal sac usually present with a painful lump at the side of the nose adjacent to the lower lid (Fig. 21.13b). This should be treated with oral broad-spectrum antibiotics such as cefalexin, and patients should be watched carefully for signs of cellulitis. All patients should be referred to the ophthalmologist as some have an underlying mucocele or dilated sac, and will require surgery.

Blepharitis. This is an extremely common condition where inflammation of the lid margins may involve the lashes and lash follicles (Fig. 21.14a) resulting in styes, or inflammation and blockage of meibomian glands (Fig. 21.14b) leading to chalazion (Fig. 21.14c). Common underlying causes of blepharitis include meibomian gland dysfunction, seborrhoea and Staphylococcus aureus infection. Patients can be asymptomatic or complain of itchy, burning eyes because of tear film instability resulting from meibomian gland dysfunction. Staphylococcus aureus is frequently responsible for chronic blepharo-conjunctivitis and some patients may develop keratitis in the cornea (Fig. 21.15).

Treatment of blepharitis. Lid hygiene is the mainstay of treatment as it helps to reduce the bacterial load and unblock meibomian glands. A short course of topical chloramphenicol or fusidic acid is useful in chronic cases but in severe cases or cases where acne rosacea is suspected, oral doxycycline may be required. Some patients are left with a lump once the acute inflammatory phase has subsided. Most of these patients find the lump, or chalazion, cosmetically unacceptable and require incision and curettage. People with keratitis should be referred to the ophthalmologist for topical steroids.

Conjunctivitis

The commonest cause of a red eye, inflammation of the conjunctiva can arise from a number of causes, with viral, bacterial and allergic being the commonest. Common features in all types include soreness, redness and discharge, and in general the visual acuity is good. History should include the speed of onset of the inflammation, the colour and consistency of the discharge, whether the eye is itchy, and if there has been a recent history of a cold or sore throat. In the neonate it is vital to exclude gonococcal or chlamydial conjunctivitis associated with maternal sexually transmitted infection. The differential diagnosis of conjunctivitis is shown in Table 21.5.

Bacterial conjunctivitis

Bacterial conjunctivitis is uncommon, making up 5% of all cases of conjunctivitis. In the vast majority of patients it causes a sore or gritty eye in the presence of good vision. Bacterial conjunctivitis is invariably bilateral and should be suspected when conjunctival inflammation is associated with a purulent discharge.

Chlamydial conjunctivitis

Chlamydia trachomatis (see p. 164) is seen in developed countries as a sexually transmitted infection that is most prevalent in sexually active adolescents and young adults. Direct or indirect contact with genital secretions is the usual route of infections but shared eye cosmetics can also be involved. Neonatal chlamydial conjunctivitis is a notifiable disease in the UK and should be suspected in newborns with a red eye. Mothers should be asked about sexually transmitted infections.

Trachoma caused by the same organism, but not usually sexually transmitted, is found mainly in the tropics and the Middle East and is a very common cause of blindness in the world (see p. 133). Chronic conjunctival inflammation causes progressive scarring, trichiasis, entropion and subsequent corneal scarring which leads to severe visual impairment or blindness from corneal opacification or ulceration.

Viral conjunctivitis

Allergic conjunctivitis

There are five main types of allergic conjunctivitis: seasonal, perennial, vernal, atopic and giant papillary. Both seasonal and perennial allergic conjunctivitis are acute allergic conjunctival disorders. Symptoms include itching and pink to reddish eyes. These two eye conditions are mediated by mast cells and can be easily treated with cold compresses, eyewashes with tear substitutes, and avoidance of allergens. The last three are difficult to treat, chronic and can be sight-threatening. They should be referred to an ophthalmologist.

Corneal disorders

Trauma

Corneal foreign body

Occasionally when something flies into the eye it gets stuck on the cornea (Fig. 21.19a). It may be associated with lacrimation and photophobia. Examination is best attempted following instillation of a topical anaesthetic and should include everting the upper lid (Fig. 21.19b). Corneal foreign bodies can usually be seen directly with a white light.

Keratitis

This is a general term to describe corneal inflammation. Common causes include herpes simplex virus, contact lens-associated infection and blepharitis. Symptoms include the sensation of a foreign body or pain (depending on the size and depth of the ulcer), photophobia and lacrimation. Vision is reduced if the ulcer affects the visual axis.

Herpes simplex keratitis

Corneal epithelial cells infected with the virus eventually undergo lysis and form an ulcer which is typically dendritic in shape (Fig. 21.17). The ulcer stains with fluorescein and can be observed easily with a blue light. Topical immunosuppression, e.g. steroid drops, or systemic immunosuppression, e.g. AIDS, can lead to the centrifugal spread of the virus such that the ulcer increases in area and is referred to as a geographic ulcer. Recurrent attacks of HSV keratitis can be triggered by ultraviolet light, stress and menstruation. All these factors are responsible for activating the virus, which normally lies dormant in the ganglion of the Vth nerve.

Contact lens-related keratitis

A small number of contact lens wearers develop infective corneal ulcers which are potentially sight-threatening (Fig. 21.21). The organisms usually responsible include Gram-positive and Gram-negative bacteria. Patients should be referred to an ophthalmologist for scraping of the ulcer and commencement of antibiotic treatment.

Cataracts

Cataract (Fig. 21.22a,b) is by far the commonest cause of preventable blindness in the world with an effective surgical treatment. In the UK, approximately 250 000 cataract operations are performed each year, making it the commonest surgical procedure.

Glaucoma

This is a group of diseases in which the pressure inside the eye is sufficiently elevated to cause optic nerve damage and result in visual field defects (Fig. 21.23). Normal intraocular pressure (IOP) is 10–21 mmHg. Some types of glaucoma can result in an IOP exceeding 70 mmHg. Glaucoma is the second commonest cause of blindness worldwide and the third commonest cause of blind registration in the UK.

Primary open-angle glaucoma (POAG)

This is the commonest form of glaucoma. High intraocular pressures result from reduced outflow of aqueous humour through the trabecular meshwork. Common risk factors include age (0.02% of 40-year-olds versus 10% of 80-year-olds), race (black Africans are at five times greater risk than whites), positive family history and myopia.

POAG causes a gradual, insidious, painless loss of peripheral visual field. It is initially asymptomatic and the central vision remains good until the end-stage of the disease. Usually glaucoma is identified during a routine ophthalmic examination. Diagnosis is only made if the IOP is measured. The optic disc is inspected and shows an enlarged cup with a thin neuroretinal rim. Visual fields are performed and show a normal blind spot with scotomas.

Acute angle-closure glaucoma (AACG)

This is an ophthalmic emergency. There is a sudden rise in intraocular pressure to levels greater than 50 mmHg. This occurs due to reduced aqueous drainage as a result of the ageing lens pushing the iris forward against the trabecular meshwork. People most at risk of developing AACG are those with shallow anterior chambers such as hypermetropes and women. The attack is more likely to occur under reduced light conditions when the pupil is dilated.

Uveitis

Uveitis is inflammation of the uveal tract, which includes the iris, ciliary body and choroid. Inflammation confined to the anterior segment of the eye (in front of the iris) is referred to as iritis or anterior uveitis, that involving the ciliary body is referred to as intermediate uveitis whilst inflammation of the choroid is termed posterior uveitis. If all three regions are involved then the term panuveitis is used. For posterior uveitis, referral to an ophthalmologist is required.

The most common symptoms of uveitis are blurred vision, pain, redness, photophobia and floaters. Each symptom is determined by the location of the inflammation such that photophobia and pain are common features of iritis whilst floaters are commonly seen with posterior uveitis.

Uveitis is commonly encountered with ankylosing spondylitis and positive HLA-B27 (see p. 527), arthritis, inflammatory bowel disease, sarcoid, tuberculosis, syphilis, toxoplasmosis, Behçet’s syndrome, lymphoma and viruses such as herpes, cytomegalovirus and HIV infection. In a number of patients no cause is found (idiopathic uveitis).

Disorders of the retina

Central retinal artery occlusion (CRAO)

This results in sudden painless severe loss of vision. Retinal arterial occlusion results in infarction of the inner two-thirds of the retina. The arteries become narrow and the retina becomes opaque and oedematous. A cherry red spot is seen at the fovea because the choroidal vasculature shows up through the thinnest part of the retina (Fig. 21.27). An afferent papillary defect is usually present.

Arteriosclerosis-related thrombosis is the most common cause of CRAO. Emboli from atheromas and diseased heart valves are other causes. Giant cell arteritis (see p. 543) must be excluded.

Age-related macular degeneration (AMD)

This is the commonest cause of visual impairment in patients over 50 years in the western world, and blind registration in this age group. It affects 10% of people over 65 years and 30% over 80 years. Mutations in various genes have been reported; fibulin 5, complement factor H, Arg 80 Gly variant of complement C3.

The cause is unknown but suggested risk factors include increasing age, smoking, hypertension, hypercholesterolaemia and ultraviolet exposure.

There are two types:

Visual loss

Every patient with unexplained sudden visual loss requires ophthalmic referral. The initial history and examination are summarized in Emergency Box 21.3.

image Emergency Box 21.3

The initial history and examination in the patient presenting with sudden loss of vision

RAPD, relative afferent papillary defect.

(After: Pane A, Simcock P. Practical Ophthalmology. Edinburgh: Elsevier Churchill Livingstone; 2005.)

The common causes of blindness are similar across the world (Box 21.3). In developing countries, trachoma due to Chlamydia trachomatis (see p. 164) is also a major cause, accounting for 10% of global blindness, as is onchocerciasis (river blindness, due to Onchocerca volvulus – see p. 154), which accounts for blindness in about 1 million people, although this is decreasing with treatment. In leprosy, 70% of patients have ocular involvement, and blindness occurs in 5–10% of these. Ocular involvement is common in cerebral malaria (see p. 144), although loss of vision is rare.

image Box 21.3 Loss of vision

summary

Painless loss of vision Painful loss of vision

Cataract

Acute angle-closure glaucoma

Open-angle glaucoma

Giant cell arteritis

Retinal detachment

Optic neuritis

Central retinal vein occlusion

Uveitis
Scleritis
Keratitis
Shingles
Orbital cellulitis
Trauma

Central retinal artery occlusion

Diabetic retinopathy

Vitreous haemorrhage

Posterior uveitis

Age-related macular degeneration

Optic nerve compression

 

Cerebral vascular disease

 

HIV infection can produce uveitis but the major problem is severe opportunistic infection of the eye when the CD4 count falls (see p. 178) and HAART is not available.

Vitamin A deficiency and xerophthalmia affects millions each year; the WHO classification of xerophthalmia by ocular signs is shown in Table 5.10 (see p. 206).

WHO lists the commonest causes of blindness across the world as cataract, glaucoma, acute macular degeneration, corneal opacity, diabetic retinopathy and infections from bacteria or parasites.