Allergic vs bacterial conjunctivitis
Structured for Australian optometry practice.
Clinical decision support only
OptoGuide™ supports professional judgement and does not diagnose or replace clinician responsibility.
Quick answer
- Itch strongly supports allergic conjunctivitis; mucopurulent discharge and lid crusting favour bacterial conjunctivitis.
- Bilateral recurrent itch with chemosis or papillae is more allergic than bacterial.
- Pain, photophobia, reduced vision, or focal staining should move the differential away from simple conjunctivitis.
- Refer when the presentation is severe, atypical, contact lens-related, or corneal involvement is present.
Common causes
- Seasonal or perennial allergic conjunctivitis.
- Bacterial conjunctivitis.
- Viral conjunctivitis as a common alternative diagnosis.
- Toxic or blepharitis-related conjunctival irritation.
Red flags (must not miss)
- Pain, photophobia, or reduced vision.
- Contact lens wear with redness or discomfort.
- Unilateral severe presentation or corneal staining.
- Membranes, significant lid swelling, or atypical recurrence.
Use OptoGuide™ to guide this decision during consult.
What to check
- Itch versus pain, and discharge pattern.
- Laterality and recurrence history.
- Lids, lashes, papillae, follicles, and chemosis.
- Corneal staining and contact lens history.
- Associated blepharitis or ocular surface disease.
When to refer
- Same day if the cornea is involved or contact lens keratitis is a concern.
- Routine escalation when symptoms are severe, recurrent, or not fitting a simple conjunctivitis pattern.
- Urgent review if acuity is reduced or photophobia is prominent.
Initial management
- Use symptom pattern and slit lamp signs rather than discharge alone.
- Separate uncomplicated conjunctivitis from corneal disease early.
- Document laterality, itch, discharge, and staining findings clearly.
Clinical basis
This guidance reflects standard optometric clinical reasoning based on:
- Australian optometry clinical practice patterns
- Australian medicines regulation and PBS prescribing context
- Common ophthalmology referral standards
- Evidence-based clinical training and practice
Use OptoGuide™ during consult for structured clinical guidance.