Infectious conjunctivitis and orbital cellulitis

• Conjunctivitis is inflammation of the transparent membrane lining the inside of the eyelids and covering the white of the eye; it is the commonest cause of a "red eye" and is usually mild and self-limited. ^[8]
• The colour and thickness of the discharge usually separates the main types: viral (watery, very contagious), bacterial (thick yellow-green "pus" that glues the lids), gonococcal (hyperacute, copious, dangerous to the cornea), chlamydial (mild mucopurulent, lasting weeks), allergic (watery/ropy, intensely itchy, not contagious).
• Viral and allergic conjunctivitis are managed without antibiotics; bacterial cases may be given topical broad-spectrum antibiotics, which may modestly shorten the illness; gonococcal and chlamydial infections need systemic antibiotics and treatment of sexual partners.
• Red flags (moderate to severe eye pain, blurred vision, photophobia, unequal pupils, swelling around the eye or worsening symptoms) mean this is not simple conjunctivitis; they need same-day ophthalmology. ^[1][8]
• Orbital cellulitis is an infection behind the orbital septum, usually spreading from the ethmoid or frontal sinuses; it is an emergency with proptosis, painful or limited eye movement, reduced vision and afferent pupillary defect, needing urgent intravenous antibiotics, imaging and sometimes drainage. ^[7]
• Trachoma, caused by repeated Chlamydia trachomatis infection of the conjunctiva, is the world's leading infectious cause of blindness and is prevented and treated by the SAFE strategy. ^{[5][6] [8]}

By the end of this page you should be able to:

1. Tell viral, bacterial, gonococcal, chlamydial and allergic conjunctivitis apart from the history and examination, and name three red flags that move the diagnosis away from simple conjunctivitis.
2. Explain why antibiotics help bacterial but not viral or allergic conjunctivitis, and why gonococcal and chlamydial infection must be treated systemically.
3. Describe the prevention and treatment of ophthalmia neonatorum caused by Neisseria gonorrhoeae and Chlamydia trachomatis.
4. Outline the SAFE strategy for trachoma and the antibiotic regimens it uses.
5. Distinguish preseptal from orbital cellulitis in a patient with lid swelling, and interpret the eye-movement, pupil and vision findings.
6. Carry an orbital cellulitis case through admission, broad-spectrum intravenous antibiotics, imaging, escalation to drainage and follow-up.
7. Adapt the above to a low-resource setting.

Conjunctivitis is the commonest eye problem a generalist meets, and it is the reason for a large share of primary care visits and a corresponding economic burden. ^[8] Most cases are mild and pass within a week or two, but three related conditions must not be missed: gonococcal conjunctivitis, which can perforate the cornea; neonatal ophthalmia; and orbital cellulitis, which can damage vision, spread to the cavernous sinus and meninges and kill. ^[2][3][7]

This page also covers orbital cellulitis, because the same patient who is thought to have simple "pink eye" may instead have an infection that has already crossed the orbital septum.

The useful clinical division is by cause, because that decides treatment. Viral, bacterial, gonococcal, chlamydial and allergic forms are the ones covered here; non-infectious causes such as toxic, dry eye and auto-immune disease exist but are not covered in depth. ^[8]

Two prevention strategies apply. Gonococcal ophthalmia is largely prevented by prenatal screening and treatment of pregnant women for gonorrhoea plus a single application of erythromycin 0.5% ophthalmic ointment into both eyes of every newborn within 24 hours of birth, ideally in the delivery room, and irrespective of mode of delivery. ^[2] Erythromycin prophylaxis does not prevent chlamydial ophthalmia, so the control of chlamydial disease in neonates depends on screening pregnant women at risk (for example women under 25 years, and others with new or multiple partners, a partner with an STI, or residence in a high-prevalence community) and treating them before delivery. ^[4]

Where erythromycin ointment is unavailable, infants at high risk (mother at risk or no prenatal care) may be given ceftriaxone 25 to 50 mg per kg by the intravenous or intramuscular route as a single dose, not exceeding 250 mg. ^[2]

The orbit drains through the superior and inferior ophthalmic veins into the cavernous sinus; this venous system has no valves, so infection can spread backwards in both preseptal and orbital cellulitis to cause cavernous sinus thrombosis. ^[7]

EyeWiki and WHO use the simplified trachoma grading scheme, which is worth remembering for examinations:

• Viral conjunctivitis is the commonest overall cause of infectious conjunctivitis; adenoviruses account for up to 90% of viral cases. ^[8]
• Bacterial conjunctivitis is less common than viral in adults but more common in children, in whom minor epidemics occur. ^[8]
• Allergic conjunctivitis is encountered in nearly half of the population (seasonal and perennial forms) and is the commonest non-infectious conjunctivitis. ^[8]
• Trachoma is a public health problem in at least part of 29 countries; 92 million people live in endemic areas at risk of blindness, about 1.9 million are already blind or visually impaired, and Africa is the most affected continent. 33 countries (including several in Africa, Asia and the Americas) have been validated by WHO as having eliminated trachoma as a public health problem. Women are blinded up to 4 times as often as men. ^[5]
• Gonococcal conjunctivitis in adults and children is uncommon but dangerous. ^[3]
• Cost. Treating bacterial conjunctivitis in the United States alone costs about 857 million US dollars a year, and 60% of patients with acute conjunctivitis receive antibiotic drops, mostly prescribed by non-ophthalmologists. ^[8]
• Orbital cellulitis. A subperiosteal or orbital abscess complicates about 10% of cases, and 75% of patients have leukocytosis. ^[7]

Viral. Adenovirus (most common, with pharyngoconjunctival fever and epidemic keratoconjunctivitis serotypes); herpes simplex virus (1.3 to 4.8% of acute cases, unilateral follicular, associated vesicles); varicella zoster; enterovirus (acute haemorrhagic conjunctivitis); molluscum contagiosum; and incidental RNA viruses including SARS-CoV-2. ^[8]

Bacterial. Staphylococcus species, Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis and Gram-negative coliforms. Risk is higher with poor tear production, epithelial barrier disruption, abnormal adnexal anatomy, trauma and immunosuppression. ^[8]

Methicillin-resistant Staphylococcus aureus (MRSA) accounts for 3 to 64% of staphylococcal conjunctival infections and is treated with fortified vancomycin eye drops or ointments. ^[8]

Gonococcal. Direct contact, oculogenital spread and fomites; prevalence in neonates depends on maternal infection and on whether pregnant women are screened and treated. ^[2][8]

Chlamydial (adult inclusion). Serotypes D to K, acquired by oculogenital spread; simultaneous genital infection is found in up to 54% of men and 74% of women. ^[8]

Trachoma. Serotypes A, B, Ba and C, transmitted by eye-hand-eye contact, fomites and eye-seeking flies, in households with crowding, poor water, poor sanitation and poor facial hygiene. ^[5][8]

Allergic. Seasonal (pollens), perennial (dust mites, animal dander, feathers), vernal (young males in warm climates), atopic (adults with atopic dermatitis) and giant papillary (contact lens related). ^[8]

Orbital cellulitis. Most commonly a bacterial infection spreading from the adjacent ethmoid or frontal sinuses through the thin lamina papyracea (in children under 10 the ethmoid sinus is dominant). Other sources are lid skin, dacryocystitis, dental infection, recent trauma or surgery, foreign body, haematogenous spread, and endophthalmitis or dacryoadenitis. ^[7]

Adenovirus replicates in the conjunctival epithelium, produces follicular inflammation and, in epidemic keratoconjunctivitis, replicates in the corneal epithelium and produces sub-epithelial infiltrates 7 to 10 days later that can scar and cause photophobia and astigmatism. Herpes simplex and varicella zoster attack the epithelium directly. Bacteria colonise or overgrow from the lid margin flora; when the surface defences (tear film, epithelium) are disrupted they proliferate and produce a mucopurulent reaction. C. trachomatis is an obligate intracellular organism that survives in epithelial cells; repeated infection drives lymphoid follicles, then fibrosis, cicatricial entropion and corneal damage. Allergic disease is an IgE-mediated (and in vernal disease mixed IgE and non-IgE) mast cell response, with histamine, prostaglandins and leukotrienes in the tear film. ^[8]

Sinus infection breaches the lamina papyracea into the orbit, where inflammation and pus expand in a rigid bony space with no room for swelling; pressure and oedema push the eye forwards (proptosis), congest the venous and arterial supply, restrict the extra-ocular muscles and can compress the optic nerve. Because the orbital veins are valveless, infection can propagate posteriorly to the cavernous sinus, and through the cribriform plate and posterior wall of the frontal sinus into the intracranial cavity, producing meningitis, subdural abscess or brain abscess. ^[7]

Symptoms that patients report and that the clinician can use to point toward the cause:

• Redness, grittiness and watering in both or one eye, usually mild, with vision preserved.
• Eyelids glued together on waking occurs in both viral and bacterial disease; mattering on waking is a strong pointer to bacterial infection. ^[8]
• Watery discharge that spreads from one eye to the other after 24 to 48 hours favours viral rather than bacterial. ^[8]
• Thick yellow-green discharge favours bacterial. ^[1]
• Intense itching is the signature of allergic disease. ^[8]
• Recent cold or sore throat, or a sick contact, favours viral; otitis media or upper respiratory infection in a young child favours H. influenzae conjunctivitis. ^[8]
• Concurrent genital discharge, dysuria or a sexual partner with an STI must prompt consideration of gonococcal and chlamydial infection in adults. ^[3][4][8]
• Slow onset, one eye, with follicles lasting weeks to months is typical of adult inclusion conjunctivitis. ^[8]

Moderate to severe eye pain, blurred or reduced vision, increased photophobia, intense redness, symptoms that worsen rather than improve, unequal pupils, a painful pupillary reaction, anisocoria and any orbital sign should never be dismissed as simple conjunctivitis. They can indicate uveitis, keratitis, scleritis, glaucoma, endophthalmitis or orbital disease. ^[1][8]

Presentation is a painful red eye with lid oedema in a child or adult with a recent upper respiratory infection. Ask about headache, orbital pain, double vision, fever, lethargy, change in vision, pain on moving the eye, nasal discharge or stuffiness, tooth or facial pain, recent trauma or surgery, diabetes and immune status, and whether there are contacts with methicillin-resistant S. aureus. ^[7]

Examination that must be performed and documented:

• Best-corrected visual acuity and colour vision (optic nerve function).
• Pupillary responses, specifically a relative afferent pupillary defect.
• Proptosis measurement (Hertel exophthalmometry).
• Extra-ocular motility and pain with movement.
• Intraocular pressure (raised with venous congestion).
• Direction of globe displacement (a superior subperiosteal abscess displaces the globe downwards).
• Resistance to retropulsion on palpation; unilateral or bilateral involvement (bilateral is virtually diagnostic of cavernous sinus thrombosis). ^[7]
• Anterior segment and dilated fundus examination for exposure keratopathy or optic neuropathy. ^[7]

On slit-lamp examination, viral disease shows follicles, sometimes pseudomembranes in epidemic keratoconjunctivitis, and later corneal sub-epithelial infiltrates. Bacterial disease shows papillary reaction and mucopurulent discharge. Chlamydial (adult inclusion) disease shows a follicular reaction that may last for weeks. Allergic disease shows chemosis, papillae (cobblestoning in vernal disease) and in severe or vernal disease superior limbal Horner-Trantas dots. ^[8]

Serious causes of a red eye must be excluded, because they present with pain, photophobia or blurred vision rather than with preserved vision and discharge. ^[8]

Contact lens over-wear in particular makes every "conjunctivitis" suspicious for infectious keratitis, and such patients need a slit-lamp examination before being managed as conjunctivitis. ^[8]

Most cases are diagnosed clinically. Investigation is reserved for specific situations. ^[8]

• Cultures of the discharge are taken for suspected infectious neonatal conjunctivitis, recurrent or treatment-resistant disease, severe purulent discharge, and cases suspicious for gonococcal infection. Swabs should be taken before antibiotics are started, and Sabouraud plates if fungus is suspected. ^[8]
• Gram stain and culture of conjunctival exudate showing intracellular Gram-negative diplococci is strongly suggestive of N. gonorrhoeae. ^[2]
• Nucleic acid amplification tests (NAAT) for C. trachomatis and N. gonorrhoeae (vaginal, urine or conjunctival specimens where validated) and for viruses; culture is still the definitive method for chlamydial pneumonia in infants. ^[8]
• Rapid in-office adenovirus antigen tests are available but have only moderate sensitivity (about 40 to 50%) and good specificity, so a negative result needs confirmation by PCR in doubtful cases. ^[8]
• Skin or serum allergy testing may help in suspected allergic conjunctivitis, but the diagnosis is clinical. ^[8]

Admission is warranted in all cases. Investigations: full blood count with differential, blood cultures, and nasal and throat swabs; imaging to confirm orbital involvement and look for complications. ^[7]

Computed tomography of the orbit is the imaging modality of choice: it is usually available urgently, shows sinusitis, stranding of orbital fat, subperiosteal abscess, orbital abscess and intracranial extension. ^[7] Magnetic resonance imaging is a useful adjunct when cavernous sinus thrombosis is suspected, because CT is less sensitive for that. ^[7]

No imaging is needed for straightforward inclusion conjunctivitis.

There is no antiviral that helps in ordinary adenoviral conjunctivitis. Treatment is supportive: frequent artificial tears, antihistamine-containing drops, cool compresses, hand washing, isolation from school or work until the eyes are no longer red with discharge, and removal of contact lenses and eye make-up. Topical and oral antivirals are not useful. Antibiotics do not help viral disease and can cause surface toxicity and encourage resistance. ^[1][8]

Specific measures for adenoviral epidemic keratoconjunctivitis:

• Peel pseudomembranes at the slit lamp after topical anaesthesia to relieve discomfort and prevent scarring.
• Topical corticosteroids are reserved for membrane formation or sub-epithelial infiltrates with severe photophobia or reduced vision, and are used cautiously because they prolong viral shedding and can raise intra-ocular pressure. Combination povidone-iodine and dexamethasone preparations are under investigation.
• Sub-epithelial infiltrates may be treated with cyclosporine or tacrolimus drops under specialist care. ^[8]

Herpetic conjunctivitis is treated with topical antiviral agents (ganciclovir, trifluridine, idoxuridine, vidarabine) to reduce viral shedding and the risk of keratitis. ^[8]

The illness is self-limited in most cases: more than 60% cure within 1 to 2 weeks even without antibiotics. ^[8] Antibiotics shorten it. A meta-analysis of 11 randomised trials (3,673 patients) showed that topical antibiotics increased clinical improvement by about 10% compared with placebo, across 2-to-5-day and 6-to-10-day regimens. ^[8] All broad-spectrum preparations (aminoglycosides, fluoroquinolones, macrolides, sulfonamides, trimethoprim/polymyxin B) appear similarly effective; choice depends on availability, allergy, local resistance and cost. ^[8]

A practical antibiotic guide for bacterial conjunctivitis (one drop to each affected eye, unless stated otherwise, for about one week): ^[8]

More than 60% of cases cure spontaneously within 1 to 2 weeks, and no sight-threatening complication was reported in the placebo arms of the meta-analysed trials. ^[8] Antibiotics are additionally justified when there is severe disease, contact lens wear, dry eye, immunocompromise, an outbreak, or a health worker or caregiver who must return to work. ^[8]

Gonococcal infection of the conjunctiva is a hyperacute, purulent infection with a high risk of corneal perforation. Adults are treated with ceftriaxone 1 g intramuscularly as a single dose plus 1 g of oral azithromycin (which covers the frequently co-existing chlamydial infection), and saline lavage of the eye may be considered. The evidence is limited (a single study of 12 adults), so management should be discussed with an infectious disease specialist. ^[3][8]

Gonococcal. Ceftriaxone 25 to 50 mg per kg intravenously or intramuscularly as a single dose, not exceeding 250 mg, or cefotaxime 100 mg per kg for neonates who cannot receive ceftriaxone because of concurrent intravenous calcium. Topical antibiotics alone are inadequate. One dose is curative. Infants should also be screened for disseminated infection (sepsis, arthritis, meningitis) and managed with an infectious disease specialist; their mothers and the mothers' partners must be tested and treated. ^[2]

Chlamydial. Erythromycin base or ethylsuccinate 50 mg per kg per day by mouth, in four divided doses, for 14 days. Topical antibiotics alone are inadequate. Efficacy is only about 80%, so a second course may be needed and infants require follow-up for response; chlamydial pneumonia (staccato cough, tachypnoea, infiltrates in an infant aged 1 to 3 months) must be considered and treated with the same regimen. Concurrent chlamydial conjunctivitis is a clue that up to 20% of neonates exposed to C. trachomatis develop pneumonia. ^[4][8]

Erythromycin (and azithromycin) given to infants under 6 weeks has been associated with infantile hypertrophic pyloric stenosis, so treated infants should be followed for vomiting. ^[4]

Trachoma control is built on the SAFE strategy endorsed by WHO: Surgery for trichiasis, Antibiotics for infection, Facial cleanliness and Environmental improvement (clean water and sanitation). ^[5][6][8]

Antibiotic treatment is either azithromycin as a single oral dose of 20 mg per kg of body weight (maximum 1 g in adults) or tetracycline 1% ointment to both eyes twice daily for 6 weeks. ^[6][8] Mass drug administration with single-dose azithromycin reduces the prevalence of active trachoma and ocular infection in communities at 12 months, although it also increases community resistance of Streptococcus pneumoniae, Staphylococcus aureus and Escherichia coli to macrolides. ^[6] Trichiasis is corrected surgically (lid rotation by tarsal fracture; epilation for selected patients). ^[5]

Systemic treatment is essential because the infection is mucosal and sexual: doxycycline 100 mg by mouth twice daily for 7 days or azithromycin 1 g by mouth once, with doxycycline preferred when rectal infection is likely. ^[4][8] Topical antibiotics add nothing. Sexual partners must be treated and gonococcal co-infection excluded. ^[8] Pregnant women are treated with azithromycin 1 g or amoxicillin 500 mg three times daily for 7 days, with test of cure at 4 weeks. ^[4]

Identification and avoidance of the allergen; cold compress and tear substitutes; topical antihistamines, mast-cell stabilisers and dual-action drops; short courses of topical corticosteroids for severe (vernal, atopic) disease under ophthalmology supervision. Contact lens-related giant papillary conjunctivitis improves when lens wear is changed or paused. ^[8]

Every case needs hospital admission, broad-spectrum intravenous antibiotics, and imaging. ^[7]

• Antibiotics. In infants a third-generation cephalosporin (cefotaxime, ceftriaxone or ceftazidime) plus a penicillinase-resistant penicillin; in older children, where sinusitis is most commonly aerobic and anaerobic, clindamycin is another option and metronidazole is increasingly used; vancomycin is added where MRSA is suspected. Therapy is modified by culture and sensitivity, and can be stepped down to oral antibiotics once clinical improvement has been documented after 48 hours of intravenous treatment. ^[7]
• Intravenous corticosteroids. May be of benefit in paediatric orbital cellulitis with subperiosteal abscess. ^[7]
• Imaging. CT of the orbit is obtained to identify sinus disease, fat stranding, abscess and intracranial extension; MRI (or MR venography) is added when cavernous sinus thrombosis is suspected. ^[7]
• Surgery. A subperiosteal or orbital abscess develops in about 10% of cases; drainage is advised after intravenous antibiotics have been given for 24 to 48 hours with progression, or immediately if there is intracranial extension, optic nerve compromise (reduced vision or an afferent pupillary defect), clinical deterioration despite 48 hours of intravenous antibiotics, anaerobic infection (gas in the abscess on CT), or recurrence of an abscess after prior drainage. ^[7]
• Observation only (intravenous antibiotics without immediate drainage) is reasonable when all of the following hold: the child is under 9 years; no intracranial involvement; a medial-wall abscess of moderate or smaller size; no vision loss or afferent pupillary defect; no frontal sinus involvement; and no dental abscess. ^[7]
• Cavernous sinus thrombosis is suspected when orbital disease is bilateral; management is with broad intravenous antibiotics covering sinus flora and appropriate anticoagulation decisions in consultation with neurology. ^[7]
• Multidisciplinary care. Ophthalmology, paediatrics, ENT, infectious disease, and neurosurgical input as indicated. ^[7]

Visual acuity, pupillary responses, motility and proptosis should be re-documented daily, and at discharge. Repeat imaging is needed if clinical deterioration occurs. ^[7]

Every case of suspected gonococcal or neonatal conjunctivitis, any conjunctivitis with a red flag (pain, reduced vision, photophobia, severe swelling), membranous/pseudomembranous conjunctivitis, recurrent or chronic disease, and every case in which a therapeutic contact lens or steroid may be needed should be seen by ophthalmology. ^[1][8]

• Viral. Corneal sub-epithelial infiltrates with scarring, photophobia, astigmatism and prolonged visual loss in epidemic keratoconjunctivitis; symblepharon from true membranes. ^[8]
• Bacterial. Keratitis and, rarely, corneal perforation (especially contact lens wearers, dry eye, immunocompromise). ^[8]
• Gonococcal. Rapid corneal melting and perforation, even in adults, and disseminated infection (sepsis, arthritis, meningitis) in neonates. ^[2][3][8]
• Chlamydial (adult). Chronic follicular disease; untreated neonatal disease produces conjunctival and corneal scarring; pneumonia in roughly 15 to 20% of exposed neonates. ^[4][8]
• Trachoma. Progressive scarring, cicatricial entropion, trichiasis and corneal opacification, producing the leading infectious cause of blindness worldwide. ^[5][8]
• Allergic. Corneal involvement (vernal) can scar and threaten vision. ^[8]

Severe exposure keratopathy, ulcerative keratitis, secondary glaucoma, septic uveitis or retinitis, exudative retinal detachment, optic neuropathy, panophthalmitis, cranial nerve palsy, orbital apex syndrome, subperiosteal and orbital abscess, central retinal artery or vein occlusion, blindness, cavernous sinus thrombosis, meningitis, subdural or brain abscess and death. ^[7]

Conjunctivitis of all types is usually self-limited and curable without sequelae. ^[8] Orbital cellulitis treated promptly and aggressively, medically and surgically when needed, has an excellent prognosis. ^[7]

• Neonates. Ophthalmia neonatorum is avoided by prevention: erythromycin prophylaxis for gonococcus and prenatal detection and treatment for chlamydia. Treatment is systemic in both (see above), because topical antibiotics alone are inadequate. ^[2][4]
• Pregnancy and breastfeeding. Chlamydial infection is treated with azithromycin or amoxicillin, with test of cure at 4 weeks and re-testing in the third trimester and at delivery; doxycycline is contraindicated in later pregnancy. ^[4] Gonococcal disease in pregnancy is treated with ceftriaxone; advice on cephalosporin allergy should be sought from an infectious disease specialist. ^[2][3]
• Children under 9 with orbital cellulitis and a medial-wall abscess of moderate size are the group in which intravenous antibiotics alone, without immediate drainage, may succeed. ^[7]
• Contact lens wearers. Any conjunctivitis in a lens wearer must be assessed for keratitis before being attributed to benign conjunctivitis. ^[8]
• Older adults and the immunocompromised. Bacterial and fungal orbital infection (mucormycosis, aspergillosis) and severe MRSA infection are more likely; a black nasal or palatal eschar suggests fungal disease and is an emergency. ^[7]
• Populations in trachoma-endemic settings. Mass treatment plus WASH measures benefit whole communities; women and children carry the greater burden. ^[5]

• Most conjunctivitis is diagnosed clinically without equipment. Antibiotics should be reserved for clearly bacterial cases (thick mucopurulent discharge, mattering on waking, bilateral disease in a child) when available: a 7-day course of a broad-spectrum drops or ointment, or even a single bottle prescribed for both eyes. ^[8]
• Where laboratory testing is unavailable, take swabs only in neonates and in severe or atypical cases, and store them for referral.
• Neonatal gonococcal prophylaxis uses erythromycin 0.5% ointment, one application, if it can be obtained; if it is unavailable and the mother is at risk or received no prenatal care, a single dose of ceftriaxone 25 to 50 mg per kg intravenously or intramuscularly (maximum 250 mg) covers both prophylaxis and early treatment. ^[2]
• Chlamydial control depends on screening pregnant women at risk and treating them, and giving erythromycin 50 mg per kg per day by mouth for 14 days to affected infants; infants must be followed up because about one in five courses fail. ^[4]
• Trachoma is managed by SAFE: single-dose azithromycin (donated through the International Trachoma Initiative), eyelid surgery through established programmes, face washing with available water, and latrine construction. ^[5][6]
• Orbital cellulitis: admit, obtain blood cultures and nasal and throat swabs, start a third-generation cephalosporin plus a penicillinase-resistant penicillin (infants) or clindamycin or metronidazole (older patients, sinus source), and add vancomycin where MRSA is suspected. ^[7]
• Computed tomography may not be available; careful daily clinical examination (visual acuity, pupil, motility, proptosis) with documented trends is the main tool, and deterioration despite 48 hours of intravenous antibiotics, or any optic nerve or intracranial sign, is an indication to transfer to a surgical centre if possible. ^[7]

Planned follow-ons include keratitis and corneal ulceration, blepharitis, dry eye disease, anterior uveitis, scleritis, endophthalmitis, acute sinusitis and its complications, preseptal cellulitis, gonorrhoea, chlamydial infection, trachoma, allergic eye disease, Stevens-Johnson syndrome and orbital apex syndrome. Links will be added once those topics are published.

• Conjunctivitis is inflammation of the conjunctiva; viral adenovirus is the commonest cause, and most cases resolve within 1 to 2 weeks. ^[1][8]
• Discharge and itching separate the types: viral (watery), bacterial (purulent, gluing), gonococcal (hyperacute purulent), chlamydial (mild persistent mucopurulent), allergic (itchy, watery or ropy). ^[1][3][8]
• Viral conjunctivitis has no useful antibiotic or antiviral; it is managed with tears, cool compresses and hygiene. ^[1][8]
• Bacterial conjunctivitis is self-limited in over 60% of cases within 1 to 2 weeks, and broad-spectrum topical antibiotics shorten it slightly (about 10% more improve, compared with placebo). ^[8]
• Gonococcal conjunctivitis is an eye-threatening emergency treated with ceftriaxone (1 g intramuscularly in adults; 25 to 50 mg per kg intravenously or intramuscularly in neonates) plus saline lavage and coverage for chlamydia; topical antibiotics alone are inadequate. ^[2][3][8]
• Adult chlamydial inclusion conjunctivitis needs systemic doxycycline or azithromycin; topical treatment adds nothing; treat the partners and test for gonococcal co-infection. ^[4][8]
• Neonatal chlamydial ophthalmia is treated with erythromycin 50 mg per kg per day by mouth for 14 days; efficacy is about 80%, so follow-up is essential. ^[4][8]
• Ophthalmia neonatorum is prevented by prenatal screening and treatment and by erythromycin 0.5% ointment in every newborn's eyes; erythromycin prophylaxis does not prevent chlamydial disease. ^[2][4]
• Trachoma, from repeated Chlamydia trachomatis infection, is the leading infectious cause of blindness; SAFE provides azithromycin 20 mg per kg (maximum 1 g) once, or tetracycline 1% ointment twice daily for 6 weeks, plus surgery for trichiasis and WASH measures. ^[5][6][8]
• Red flags (pain, reduced vision, photophobia, unequal pupils, orbital signs) are not conjunctivitis; same-day ophthalmology. ^[1][8]
• Orbital cellulitis is an infection that most often (over 80% of cases) arises from ethmoid or frontal sinus disease, lying behind the orbital septum; it presents with proptosis, pain on and limitation of eye movement, reduced vision and afferent pupillary defect, and requires admission, broad-spectrum intravenous antibiotics, computed tomography and sometimes drainage. ^[7]
• The venous drainage of the orbit is valveless, so orbital infection can reach the cavernous sinus and cause meningitis, abscess or death. ^[7]
• In adults MRSA accounts for 3 to 64% of staphylococcal conjunctivitis and is treated with fortified vancomycin. ^[8]
• Orbital infection in infants uses a third-generation cephalosporin plus a penicillinase-resistant penicillin; in older children clindamycin or metronidazole for the sinus flora; vancomycin if MRSA is suspected. ^[7]