Conjunctivitis subtypes

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Conjunctivitis is inflammation of the conjunctival surface over the sclera and inside the eyelids. Patients often use the term for any red eye, so first establish that the problem is confined to this surface. Ask about discomfort, visual function, light sensitivity, contact-lens use, trauma, chemical exposure and recent ocular procedures before concentrating on discharge. Document visual acuity separately in each eye. A watery film or crust may transiently blur vision, but a persistent reduction after blinking or gentle cleaning needs another explanation.

Viral disease commonly begins in one eye and spreads to the other, sometimes alongside an upper respiratory illness or exposure to someone with similar symptoms. Bacterial disease more often produces sticky mucopurulent discharge and lids stuck together after sleep. Allergy usually affects both eyes and produces prominent itch, watering and associated nasal symptoms. These patterns change probability rather than proving an organism. Chronic unilateral disease, repeated treatment failure or substantial follicular inflammation should prompt consideration of chlamydia, eyelid disease, a retained foreign body or lacrimal drainage pathology.

Initial management combines diagnostic safety, symptom relief and transmission advice. Clean crusts gently with cooled boiled water and a separate clean pad for each eye; a cool compress may relieve irritation. Wash hands regularly, avoid rubbing the eyes and do not share towels or eye cosmetics. Contact lenses should be removed until the episode is resolved and the patient has appropriate advice about safe resumption. Routine exclusion from school or work is unnecessary when the person feels well, although local outbreak or occupational advice may add specific requirements.

Key points

Viral, bacterial and allergic conjunctivitis overlap clinically; discharge colour alone does not reliably determine the cause.
Itching that dominates bilateral watery symptoms supports allergy, particularly with rhinitis and a seasonal or exposure-related pattern.
Uncomplicated conjunctivitis causes irritation or grittiness with a clear cornea and preserved visual acuity after discharge is removed.
Most ordinary infective episodes improve without antibiotics, so treatment decisions should reflect severity, persistence and individual circumstances.
Chloramphenicol is an option for selected uncomplicated bacterial infection; it does not treat viral or allergic disease.
Do not start a steroid-containing eye preparation for an undiagnosed red eye.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Infectious causes

Viruses and ordinary bacterial organisms cause many acute episodes. Gonococcal and chlamydial disease are less common but require different testing and treatment because topical routine care may be inadequate.

Allergic and irritant exposure

Airborne allergens provoke itching and bilateral inflammation in susceptible people. Cosmetics, chemical irritants and medication toxicity can produce overlapping redness without an infectious cause.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Surface vascular response
Inflammatory mediators dilate conjunctival vessels and increase vascular permeability. This produces visible redness and swelling while uncomplicated disease leaves the deeper eye and corneal transparency intact.
2
Discharge formation
Tears, mucus and inflammatory cells contribute in different proportions to watery or sticky discharge. The appearance reflects the surface response and cannot identify a pathogen with certainty.
3
Allergic inflammation
Allergen-driven mast-cell activation releases mediators that cause itching, vasodilatation and watering. Associated nasal symptoms and recurrent exposure patterns help connect ocular symptoms to an allergic mechanism.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Viral pattern

Watery discharge, grittiness, sequential bilateral involvement and recent respiratory symptoms favour viral infection; preauricular tenderness can support the pattern without excluding other disease.

Bacterial pattern

Sticky discharge that repeatedly returns and eyelids glued on waking support bacterial infection, but substantial pain or corneal change requires reassessment of the diagnosis.

Allergic pattern

Bilateral itch with watering, chemosis and a reproducible allergen relationship is more persuasive than redness alone; ask about atopy and concurrent rhinitis.

Unusual or severe infection

Hyperacute copious pus, marked swelling, sexual exposure, prolonged unilateral symptoms or neonatal presentation changes the investigation and referral pathway.

Red flags requiring action

Pain, significant light sensitivity or vision that remains blurred after blinking and clearing discharge suggests disease beyond uncomplicated conjunctivitis.
A red eye in a contact-lens wearer may be microbial keratitis even when discharge initially suggests conjunctivitis.
Marked purulence with rapid progression, corneal haze or a red sticky eye in a newborn requires same-day assessment.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Visual acuity and pupil examinationFirst step
Why
Identify loss of function inconsistent with simple surface inflammation.
Interpretation and limitations
Record each eye with usual correction; persistent visual reduction, an abnormal pupil or an afferent defect warrants urgent ophthalmic assessment.
02
Corneal inspection and fluorescein when trained
Why
Look for epithelial damage or an alternative corneal diagnosis.
Interpretation and limitations
An infiltrate, ulcer, dendritic staining or significant epithelial defect redirects care towards an urgent corneal pathway rather than uncomplicated conjunctivitis.
03
Conjunctival microbiology in selected cases
Why
Identify pathogens when severity or persistence changes management.
Interpretation and limitations
Routine mild disease needs no swab, but severe, recurrent, treatment-resistant or neonatal infection merits samples directed by the assessing specialist.
04
Sexual-health testing when clinically indicated
Why
Investigate suspected gonococcal or chlamydial ocular infection appropriately.
Interpretation and limitations
Arrange suitable ocular and genital testing with specialist advice; sampling must not postpone urgent assessment of hyperpurulent disease threatening the cornea.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Microbial keratitis

Corneal infection produces pain, light sensitivity, epithelial damage or an infiltrate, often with reduced vision. Contact-lens wear substantially increases concern when evaluating an apparently conjunctival red eye.

Anterior uveitis

Intraocular inflammation can present with redness and watering but typically adds photophobia, aching pain, ciliary injection or pupil abnormality. Slit-lamp examination identifies anterior chamber inflammation.

Blepharitis and dry eye

Lid-margin debris, recurrent burning and symptoms that fluctuate with blinking suggest chronic ocular-surface disease. Secondary conjunctival redness can lead to repeated unnecessary treatment for infection.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Ordinary infectionSupport recovery and review the antibiotic indicationFirst stepExamination supports uncomplicated conjunctivitis with preserved vision and no corneal or contact-lens concern.

1Explain that many bacterial and viral episodes settle spontaneously and agree a practical symptom-relief plan.
2Consider immediate or delayed topical antibiotic treatment when bacterial infection is sufficiently likely and clinical circumstances justify it.
3Provide clear return instructions for deterioration, lack of improvement and symptoms persisting beyond the expected course.

02Allergic symptomsReduce exposure and treat the allergic responseItch, bilateral watering and allergen exposure dominate without pain, visual loss or corneal abnormality.

1Discuss feasible allergen reduction, cold compresses and lubricants to reduce surface irritation.
2Ask a pharmacist or prescriber to select an age-appropriate topical antihistamine or mast-cell stabiliser when simple measures are insufficient.
3Reassess persistent, severe or painful symptoms because vernal or atopic keratoconjunctivitis can involve the cornea and needs specialist care.

03High-risk presentationArrange an urgent specialist infection assessmentThere is profuse purulence, neonatal disease, a contact-lens concern or any sight-threatening examination finding.

1Contact the urgent ophthalmology service and communicate the visual acuity, corneal findings, age and relevant exposure history.
2For suspected sexually transmitted infection, coordinate systemic treatment, testing and partner management through ophthalmology and sexual-health services.
3Do not assume a standard chloramphenicol course is adequate for gonococcal disease, chlamydial infection or contact-lens-associated keratitis.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Provides topical antibacterial treatment when examination and clinical circumstances support ordinary bacterial conjunctivitis.

Chloramphenicol 1% eye ointment

For selected uncomplicated bacterial infection, apply a 1 cm ribbon inside the affected lower eyelid three to four times daily, leaving roughly four to six hours between applications, for five days.

Check allergy, relevant haematological history and product suitability. Ointment temporarily blurs vision. Seek review if symptoms worsen or fail to improve after two days; do not use this regimen for a suspected corneal ulcer.

Relieves surface irritation in viral or allergic conjunctivitis while the underlying process resolves or receives targeted treatment.

Carmellose sodium eye drops

Use one to two drops in the affected eye or eyes as needed for irritation, selecting a suitable formulation and following its opening-expiry instructions.

Avoid touching the dispenser tip to the eye and separate other eye drops by at least five minutes. Consider a preservative-free preparation when frequent use causes irritation; lubrication must not delay assessment of pain or visual loss.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Corneal involvement

Some infectious or severe allergic processes extend onto the cornea and impair vision. Increasing pain, light sensitivity or persistent visual blur signals that the original uncomplicated label needs review.

Transmission within close contacts

Contaminated hands, towels or cosmetics can spread infective conjunctivitis. Advice should make hygiene practical without implying that every case requires exclusion from normal education or employment.

Missed systemic treatment needs

Unrecognised sexually transmitted ocular infection can persist, affect partners or threaten the cornea. Treating only the eye may leave the underlying infection and reinfection risk unaddressed.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Explain that antibiotics cannot shorten an allergic or viral process; review the diagnosis when repeated courses have provided little benefit.
Advise reassessment if there is no improvement after two days of chloramphenicol, and earlier if symptoms worsen at any point.
Arrange review for symptoms that have not cleared within seven days, particularly unilateral, recurrent or persistently purulent disease.
Give an immediate return threshold for pain, photophobia, reduced vision, corneal opacity or substantial eyelid swelling, rather than waiting for a planned appointment.
For soft-lens users receiving chloramphenicol, allow at least 24 hours after the final dose and ensure the eye is clinically recovered before resumption; suspected lens-related infection needs specialist clearance.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Discharge is an imperfect discriminator

Mucus can accompany surface inflammation of different causes. Integrate itch, chronology, exposure, acuity and corneal examination instead of treating every sticky eye as proven bacterial disease.

Persistent unilateral symptoms

A recurrently treated single eye deserves inspection for a foreign body, eyelid lesion, lacrimal problem or chlamydial infection rather than indefinite empirical topical antibiotics.

School and household advice

Routine school exclusion is unnecessary for an otherwise well child, but good hand hygiene and separate towels remain useful because viral and bacterial episodes can spread.

Newborns need their own pathway

A red or sticky eye during the first month of life requires prompt clinical assessment for ophthalmia neonatorum; ordinary adult self-care and pharmacy pathways are inappropriate.

11Common pitfallsFrequent interpretation and management errors.

01
Prescribing on the basis of a telephone description of redness without checking for visual loss, photophobia, lens wear or ocular trauma.
02
Mistaking severe hyperpurulent infection for a routine bacterial episode and delaying systemic treatment or corneal assessment.
03
Using an antibiotic and steroid combination before a clinician has excluded herpetic or other microbial corneal disease.
04
Telling a patient with persistent blurred vision to finish treatment before seeking review, despite a potentially sight-threatening alternative diagnosis.