Although it is now less common in Australia, trachoma is the most prevalent eye infection in the world. Australian practitioners are more likely to encounter patients with conjunctivitis, a condition which is often treated with antibiotics even though a minority of cases are due to bacterial infection. Although it has characteristic signs, herpes simplex keratitis can be misdiagnosed as conjunctivitis. Many eye infections can be treated by general practitioners, but corneal abscesses and intraocular infections should be referred to a specialist. For example, postseptal orbital cellulitis often requires emergency surgery. Although a chalazion will eventually settle spontaneously, a recurrence is an indication for a biopsy to exclude malignancy.

Therapy for infections of the eye and its adnexae require special considerations. The wall of the eye is readily accessible to systemically administered antimicrobial drugs, but the extension of the blood brain barrier to the eye limits the choice of antibiotics if the interior of the eye requires treatment. The anterior segment of the eye, particularly the cornea, is also readily accessible to topical drugs. To avoid the possible development of resistance, antibiotics which are also used systemically are not given topically. There is also the possibility of direct toxicity.

Eyelid infections

This is the most common problem. There are many different and complicated sub classifications, but a simple division into seborrhoeic and infected blepharitis will suffice for most purposes.

Seborrhoeic blepharitis looks similar to dandruff, with desquamated flakes and a chronic redness at the base of the eyelashes. Various studies have claimed an association with bacterial colonisation, fungal colonisation, mite infestation or any number of other factors. Vigorous attention to the treatment of these supposed infections can lead to remarkable improvement in the blepharitis. However, the clinical improvement does not necessarily, or indeed usually, coincide with eradicating the infection. The traditional remedy of a dilute bicarbonate solution (1 teaspoonful in 250 mL of hot tap water) massaged along the base of the eyelashes with a pledget of clean cotton wool is still effective.

The detergent effect of baby shampoo undiluted or diluted up to 1:10 and applied via a cotton bud is more efficacious. The patient should be warned that the condition will relapse after treatment, and continued lid hygiene will be needed.

If there is staphylococcal super-infection, then the skin at the base of the eyelashes may become ulcerated and appear impetiginous. The crusting should be removed with baby shampoo before beginning a suitable treatment for impetigo. However, it is often sufficient after cleansing for the patient simply to wash their hands, apply a drop of a sulphonamide preparation or tetracycline ointment to the clean (uncharacteristically!) finger and massage the base of the eyelashes with this.

Styes and meibomian cysts
A stye is an infection, usually staphylococcal, in a lash follicle. Hot fomentations can comfort the patient and speed pointing. If the offending lash is then removed with the aid of a good light, some magnification and a pair of eyebrow tweezers or jeweller's forceps, the condition will subside rapidly and antibiotics are unnecessary.

A chalazion is a lipogranuloma of the meibomian gland in the tarsal or stiffening plate of the lid. Chalazions tend not to point, and there is usually more reaction visible on the conjunctival surface of the lid than the skin. Most will eventually settle to a small hard nodule which can be removed by excision from the conjunctival surface. A recurrence of chalazion on the same site should raise the suspicion of malignancy and a biopsy should be taken from tissue in the base.

Tear sac obstruction
Tear sac obstruction causes a watery eye which may become sticky. If this progresses to mucocoele formation, there will be a rounded swelling below the inner canthus at the medial end of the lower lid. Gentle pressure on this will confirm the diagnosis if pus emerges from the puncta onto the lid margins. This manoeuvre is a very necessary part of the treatment in babies, who may have delayed canalisation of the lower nasolacrimal duct. In the author's practice, topical framycetin is the most effective antibiotic for this condition in babies. The tear sac has to be massaged gently first for about 15 seconds to express its contents, which can then be wiped away with a clean tissue or cotton wool. A drop of framycetin is instilled (the parents should be shown how to use this rather different to handle bottle) and the tear sac again massaged to ensure that the antibiotic reaches it. After an initial 8 mL supply 4 times a day has been used up, a simple astringent drop of zinc sulphate and phenylephrine may be substituted. The hydrodynamics of massaging also assist by increasing the likelihood of canalisation of the lower end of the duct. Only 2% of affected babies are still having symptoms by their first birthday and will require probing under anaesthesia.

Adults with an infected mucocoele may develop a fistula to the skin below the inner canthus, in which case incision and drainage are the preliminary procedures required. Chronic mucocoele formation is an indication for the operation of dacryocystorhinostomy (DCR). Obstruction without mucocoele formation may respond to zinc sulphate drops used 4 times a day.

Classical erysipelas still occurs. In my practice, it often follows gardening injuries. Intramuscular benzylpenicillin remains the treatment of choice.

Orbital cellulitis may be a preseptal cellulitis with much swelling confined to the lid tissues. This is associated with a local inflammatory focus e.g. a stye or chalazion. The recommended treatment is now cefotaxime, 1 g 8 hourly intravenously, or ceftriaxone 1 g daily intravenously. If there is any suggestion of staphylococcal super infection, then flucloxacillin 1-2 g 4 hourly should be added. In children, adjust the dosage according to age.

Post-septal cellulitis is a very much more serious problem and is often associated with posterior ethmoid sinus infection, which requires surgical intervention. The lids are very tense and red, and eye movement is limited and painful. In extreme cases, vision may be compromised, particularly if an abscess forms in the orbital soft tissues. In children, a particular risk is haemophilus infection which can spread and cause meningitis. In adults, the most feared complication is cavernous sinus thrombosis. Treatment requires appropriate antibiotics, as for pre-septal cellulitis, and any requisite surgical measures for the sinusitis.

This continues to be a much misused and abused term. Many of the less common but sight-threatening conditions can be misdiagnosed as conjunctivitis.

Microbial conjunctivitis
Microbial conjunctivitis is relatively uncommon. A one year prospective study of over 400 patients with conjunctivitis attending the Royal Victorian Eye and Ear Hospital's emergency department found that only one-third had a treatable microbial cause. Fortunately, most microbial conjunctivitis is usually self-limiting and will get better even if treatment is withheld. However, it is common practice to use a broad spectrum topical antibiotic. Earlier symptomatic relief may result and almost any antibiotic can be used with the expectation of success. The two most popular are probably chloramphenicol and neomycin, and it is preferable to use either of them in a combined preparation with another antimicrobial rather than on their own. Most community organisms nowadays are sensitive to either antibiotic. If the course is limited to 5-7 days, the risk of a topical allergy from either preparation (both can cause it!) is extremely small, and the risk of idiosyncratic bone marrow depression from chloramphenicol is also very small. In some centres, the more active, but more expensive, tobramycin might be substituted. No doubt there will be pressure to use the synthetic fluoroquinolones, but placebocontrolled trials often demonstrate an independence between clinical and microbial cures. There is still a place, too, for the use of the time hallowed preparations of zinc sulphate and even dibromopropamidine. These have a mild antibacterial effect, are not associated with the development of resistance and may be bought by the patient as an over the counter preparation.

Dry eyes
The most common cause of conjunctivitis in an ageing population is that of dry eyes. For these patients, finding the appropriate artificial tear drops and using them often enough can almost become full-time occupational therapy.

Allergic conjunctivitis
This is very common in Australia, and is not confined to patients with atopy. Antibiotic treatment is not appropriate.

Viral keratoconjunctivitis
Various strains of adenovirus can cause this, with recurring epidemics. Some strains of adenovirus appear to be sensitive to zinc sulphate, others are not and there are no alternative preparations which may be used. The condition is highly infectious but self-limiting.

Neonatal conjunctivitis
The classical gonococcal ophthalmia neonatorum is extremely rare nowadays. Neonatal conjunctivitis is more likely to be chlamydial, or even from gram negative rods endemic to the nursery where the baby spent its first few days. When faced with such a patient, it is worth asking the nursery what the resident infecting organism is and if its sensitivity pattern is known. Treat chlamydial infections with erythromycin and penicillin resistant gonococcal infections with ceftriaxone or cefotaxime.

Corneal infections

Herpes simplex keratitis is probably the condition most commonly misdiagnosed as conjunctivitis. The lack of any significant discharge, the small pupil, the photophobia, the watering eye and even the discomfort should lead to a decision to instil some fluorescein to look for (easier with a blue filtered torch) the typical branching patterns of the dendritic ulcer. Untreated herpes simplex is seen rarely, except in underdeveloped countries, but carries a 90% morbidity in terms of loss of vision from scarring. The preferred treatment is acyclovir ointment applied as a 1 cm ribbon 5 times a day until at least 3 days after fluorescein ceases to stain the cornea. Recurrences are likely in half of the patients; they should keep a tube of acyclovir in their domestic refrigerator for use at the first sign of trouble. A few patients appear to have viruses which do not respond to acyclovir, and they may benefit from vidarabine ointment. A most useful adjunct in the acute phase is 1% atropine drops twice a day. This breaks the reflex pupillary spasm and watering and allows the ointment better access to the virus in the cornea. There is no place nowadays for the older and comparatively ineffective idoxuridine.

Herpes zoster ophthalmicus frequently involves the cornea, even in the absence of the classical nasociliary involvement. If slitlamp examination is used, a majority of patients show corneal micro dendrites. Topical acyclovir ointment used 4 hourly for a week can make these eyes settle materially faster. If the rash has been present for less than 3 days, then systemic treatment with acyclovir may also be worth considering, in spite of its expense. The oral dose is 800 mg 5 times a day for a week. If at first the patient is unable to take the tablets in the initial phase, intravenous dosing may be needed. The vesicles often seem to dry up much faster if cleansed with a povidoneiodine preparation. Massive lid oedema can occur even in the absence of lid vesicles, and will respond well to zinc cream or zinc and castor oil cream. Some series have suggested that the use of steroids, which has been classical in these cases, may materially worsen the risk of serious corneal recurrences, and that acyclovir on its own reduces this risk greatly.

Corneal abscess
This is becoming more common in wearers of disposable contact lenses. Pseudomonas aeruginosa and Acanthamoeba are the most feared organisms. Delay in diagnosis and appropriate treatment can lead to loss of the eye. The patient should be referred urgently for microbial investigation of a corneal scraping and treatment. Therapy includes fluoroquinolones or anti-pseudomonal penicillins with an aminoglycoside, and, for the Acanthamoeba, dibromopropamidine with neomycin and perhexylene bacquilate. The patient's contact lens, lens case, cleansing and storage solutions are usually found to be heavily contaminated reservoirs of infection.

Intraocular infection

These rare intraocular infections are dreaded complications of intraocular surgery. They may present as a fulminating abscess within the eye next day, or as a more indolent infection any time up to 6 months after operation, particularly if Staphylococcus epidermidis or Propionibacterium spp. is responsible. Pain, lid swelling, loss of vision and even pus in the eye (hypopyon) are the usual signs. Confirmation of diagnosis and the complex treatment required merit urgent referral to a specialist centre.

Candida septicaemia
Candida septicaemia can result in silting of candida at the macula and the development there of a candidoma. Clinically, this occurs most commonly in intravenous drug abusers who activate heroin with the juice from a mouldy lemon. Treatment with flucytosine and amphotericin is being replaced by fluconazole which penetrates the blood brain barrier. Happily, there does also seem to be an increased awareness within the drug abusing community of the risks of mouldy lemons.

AIDS and the eye
Around 20% of patients with AIDS will develop retinitis from CMV infection in the later stages of their disease (when the CD4 falls). The typical `cottage cheese and tomato ketchup' retinopathy may be seen with a direct ophthalmoscope when it affects the posterior pole, but peripheral lesions will only be found by searching with an indirect ophthalmoscope. These peripheral lesions are often silent. Intravenous gancyclovir or foscarnet can be dramatically effective, but need to be continued at a reduced dose for the life of the patient to minimise risk of recurrences.

Tropical eye infections
The Australian propensity to travel and the constant inflow of new Australians from all over the world mean that any medical practitioner in Australia is likely to be confronted with diseases once considered exotic.

Trachoma eradication campaigns have been very successful in Australia, but on a worldwide basis, there are probably up to 10 million people still blind from the effect of this chlamydial conjunctival infection and subsequent corneal scarring.

Onchocerciasis or African river blindness is not confined to equatorial Africa, but also occurs in Central America. It is caused by a filarial nematode and is probably responsible for blindness in 2 million people who become infected in childhood. The drug ivermectin seems to be very effective.

Parasitic disease
Aside from the severe problem of onchocerciasis, in our own community the protozoan Toxoplasma gondii and the threadworm Toxocara canis cause considerable ocular morbidity. Sundry tropical parasites, including cysticercus and fish worms, are rarely seen.

Self-test questions

The following statements are either true or false.

1. Most cases of conjunctivitis are due to bacterial infection.

2. A chalazion which recurs requires biopsy.

Answers to self-test questions

1. False

2. True