Conjunctivitis

Conjunctivitis is inflammation of the conjunctiva and one of the most common causes of a red eye encountered in primary care. The major categories relevant to outpatient practice are viral, bacterial, and allergic conjunctivitis, but red eye can also represent keratitis, corneal abrasion, uveitis, acute angle-closure glaucoma, foreign body, or other conditions requiring more urgent evaluation.

The diagnostic challenge is that viral and bacterial conjunctivitis overlap substantially in their clinical presentation. Yeu and Hauswirth (2020) emphasize that relying on nonspecific historical features or discharge alone contributes to misdiagnosis and unnecessary antibiotic use. Viral infection accounts for the majority of infectious conjunctivitis, while allergic conjunctivitis is the most common noninfectious form.

Initial Assessment of the Red Eye

Before selecting treatment, determine whether the presentation is consistent with uncomplicated conjunctivitis or suggests a more serious ocular disorder. History should address onset, unilateral versus bilateral symptoms, itching, discharge, recent upper respiratory infection, exposure to others with conjunctivitis, contact-lens use, trauma, foreign-body exposure, photophobia, pain, visual change, and prior ocular disease.

The examination should include visual acuity, pupil appearance, type of discharge, eyelid and orbital findings, and inspection for corneal involvement when appropriate. Pain or photophobia should increase concern for diagnoses such as bacterial keratitis, anterior uveitis, or acute angle-closure glaucoma rather than routine conjunctivitis (Yeu & Hauswirth, 2020).

Immediate ophthalmic evaluation is warranted for visual loss, moderate-to-severe pain, severe purulent discharge, or corneal involvement. Contact-lens wearers with a painful red eye require particular caution because their risk of bacterial keratitis and corneal infection is higher (Yeu & Hauswirth, 2020).

Distinguishing Viral, Bacterial, and Allergic Conjunctivitis

Viral Conjunctivitis

Viral conjunctivitis commonly begins in one eye and spreads to the second eye within several days. Typical findings include redness, tearing, and clear or white watery discharge. A recent upper respiratory infection, exposure to another person with conjunctivitis, and preauricular lymphadenopathy support a viral cause (Yeu & Hauswirth, 2020).

Adenovirus causes most viral conjunctivitis. The condition is highly contagious and is generally self-limited, usually improving over approximately 1–2 weeks (Hilaire & Hornecker, 2026; Yeu & Hauswirth, 2020).

Bacterial Conjunctivitis

Bacterial conjunctivitis commonly presents with conjunctival redness and mucopurulent discharge. Eyelids that are stuck or “glued” together on awakening increase the likelihood of bacterial disease, particularly when itching is absent (Hilaire & Hornecker, 2026; Yeu & Hauswirth, 2020).

Common organisms include Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae. S. aureus is more common in adults, whereas S. pneumoniae and H. influenzae are particularly important in children (Hilaire & Hornecker, 2026).

Allergic Conjunctivitis

Itching is the hallmark symptom of allergic conjunctivitis. Symptoms are usually bilateral and may include redness, tearing, chemosis, and watery or mucoid discharge. A history of allergic rhinitis, asthma, eczema, or seasonal symptom recurrence further supports an allergic cause (Hilaire & Hornecker, 2026).

Viral Conjunctivitis Treatment

Uncomplicated adenoviral conjunctivitis is treated supportively, not with antibiotics. Cold compresses and artificial tears can reduce irritation. Chilled artificial tears may provide additional symptomatic relief. Topical antibacterial drugs do not treat adenovirus and should not be prescribed simply because the eye is red (Hilaire & Hornecker, 2026; Yeu & Hauswirth, 2020).

Infection-Control Counseling

Viral conjunctivitis is highly contagious. Patients should practice careful hand hygiene, avoid sharing towels and personal items, avoid touching or rubbing the eyes, and avoid contaminating medication bottles. Contact lenses and the lens case used during active infection should be discarded when appropriate, and lenses should not be worn again until the infection has fully resolved (Hilaire & Hornecker, 2026).

Antibiotic Stewardship

Antibiotic prescribing is one of the most important clinical issues in conjunctivitis. Yeu and Hauswirth (2020) describe substantial antibiotic overuse because viral and bacterial presentations overlap and clinical diagnosis is imperfect. The practical implication is that redness plus discharge is not sufficient justification for antibiotics. Treatment should reflect the overall presentation, likelihood of bacterial infection, risk factors, severity, and potential for complications.

Routine cultures are generally unnecessary in uncomplicated cases. Culture becomes more relevant in neonates, immunocompromised patients, hyperacute presentations, severe disease, and infections that fail to respond as expected (Hilaire & Hornecker, 2026; Yeu & Hauswirth, 2020).

Acute Bacterial Conjunctivitis Treatment

Acute bacterial conjunctivitis is often self-limited, but topical antibiotics can shorten illness, reduce transmission, and reduce risk of selected complications. The choice of treatment is usually empiric and should include activity against common gram-positive organisms (Hilaire & Hornecker, 2026).

First-line options identified in Chapter 63 include polymyxin B/trimethoprim solution, polymyxin B/bacitracin ointment, and erythromycin ointment. Ointment may be easier to administer in children, although temporary blurred vision can occur. Adults may prefer drops because they interfere less with vision during the day (Hilaire & Hornecker, 2026).

Aminoglycosides such as gentamicin and tobramycin are alternatives but provide less complete gram-positive coverage and may cause corneal epithelial toxicity. Sulfacetamide is less favored because of substantial resistance (Hilaire & Hornecker, 2026).

Contact-Lens Wearers

Contact-lens use changes both the differential diagnosis and antibiotic selection. Pseudomonas must be considered because infection can be more aggressive and resistant in contact-lens wearers. The 2026 pharmacotherapy text recommends a topical fluoroquinolone when bacterial conjunctivitis occurs in a contact-lens user, is severe, or recurs because of the need for Pseudomonas coverage (Hilaire & Hornecker, 2026).

More importantly, a contact-lens wearer with pain, photophobia, decreased visual acuity, or corneal findings may have keratitis rather than uncomplicated conjunctivitis and warrants prompt ophthalmic evaluation.

Hyperacute Gonococcal Conjunctivitis

Rapid onset, copious purulent discharge, ocular tenderness, decreased vision, and marked inflammation should raise concern for Neisseria gonorrhoeae. Gonococcal infection can rapidly invade the cornea and cause perforation, making this an ophthalmic emergency rather than routine conjunctivitis (Hilaire & Hornecker, 2026; Yeu & Hauswirth, 2020).

The assigned textbook pairs ceftriaxone with topical antibiotic therapy, but current CDC guidance for gonococcal conjunctivitis in adolescents and adults recommends ceftriaxone 1 g intramuscularly as a single dose and consideration of one-time saline lavage of the infected eye. Because adult treatment data are limited and corneal injury can progress rapidly, infectious-disease and ophthalmology consultation should be considered. The presentation should also prompt evaluation and management of sexually transmitted infection and sex partners rather than treatment as isolated ocular disease (Centers for Disease Control and Prevention [CDC], 2021; Hilaire & Hornecker, 2026).

Chlamydial Conjunctivitis

Chlamydial conjunctivitis can present as persistent unilateral conjunctivitis with follicular inflammation and mild mucopurulent discharge. Because Chlamydia trachomatis is an intracellular systemic infection, topical therapy alone is insufficient. Systemic treatment is required, and concurrent genital infection should be assessed (Yeu & Hauswirth, 2020).

Conjunctivitis persisting for several weeks should prompt reconsideration of the diagnosis. Chapter 63 recommends ophthalmology referral when presumed bacterial conjunctivitis lasts 4 weeks or longer because chlamydial and other alternative etiologies must be considered (Hilaire & Hornecker, 2026).

Allergic Conjunctivitis Treatment

Treatment begins with allergen avoidance and supportive measures. Cold compresses and artificial tears can reduce itching and dilute allergens from the ocular surface. Topical antihistamines provide rapid relief, while mast-cell stabilizers suppress mediator release and are most useful when used prophylactically (Hilaire & Hornecker, 2026).

Combination antihistamine/mast-cell-stabilizing products such as ketotifen and olopatadine provide both rapid H1 blockade and longer-term suppression of mast-cell mediator release. Topical corticosteroids may be appropriate in selected severe cases, but only after herpetic disease and corneal involvement have been excluded and generally with ophthalmology involvement.

Herpetic Eye Disease

HSV and VZV deserve special attention because treating them as routine viral conjunctivitis can miss potentially vision-threatening corneal disease. HSV conjunctivitis is often unilateral with watery discharge and may be associated with vesicular eyelid lesions or dendritic epithelial lesions visible with fluorescein. Antiviral treatment may be required, particularly when the cornea is involved. Topical corticosteroids can worsen HSV disease and should be avoided unless directed by ophthalmology (Yeu & Hauswirth, 2020).

Follow-Up

Improvement should occur over the expected natural history of the suspected condition. For acute bacterial conjunctivitis, substantial improvement is generally expected within approximately 1 week. Viral conjunctivitis usually resolves within about 2 weeks. Failure to improve should prompt reconsideration of the diagnosis rather than automatic continuation or escalation of topical medication (Hilaire & Hornecker, 2026).

Patients with viral conjunctivitis who do not improve within 7–10 days or who develop visual loss should be referred to ophthalmology to evaluate for herpetic infection or another process (Hilaire & Hornecker, 2026).

Clinical Prescribing Perspective

The most important prescribing decision in conjunctivitis is often determining whether an antimicrobial is indicated at all. Watery discharge, recent URI symptoms, sequential bilateral involvement, and absence of pain or vision change support viral disease and supportive care. Mucopurulent discharge with glued eyelids increases the likelihood of bacterial conjunctivitis. Prominent bilateral itching and an atopic history support allergic conjunctivitis. A contact-lens wearer with significant pain, photophobia, or decreased vision should be evaluated for keratitis rather than treated empirically as uncomplicated conjunctivitis.

High-Yield Distinctions

  • Viral conjunctivitis: usually watery and self-limited; supportive treatment rather than topical antibiotics.
  • Bacterial conjunctivitis: mucopurulent discharge and glued eyelids increase likelihood; common first-line options include polymyxin B/trimethoprim and erythromycin.
  • Allergic conjunctivitis: itching is the strongest distinguishing symptom and symptoms are usually bilateral.
  • Contact lenses: increase concern for Pseudomonas and bacterial keratitis; significant pain or corneal findings require prompt evaluation.
  • Gonococcal conjunctivitis: hyperacute purulent presentation with risk of corneal perforation; current CDC therapy is ceftriaxone 1 g IM once, with one-time saline lavage considered and prompt specialty involvement.
  • Chlamydial conjunctivitis: requires systemic rather than topical-only therapy.
  • HSV: dendritic corneal lesions or suspected herpetic disease require ophthalmic evaluation; avoid empiric topical corticosteroids.
  • Pain, photophobia, visual loss, severe purulence, or corneal involvement are red flags for referral.
  • Antibiotic stewardship: do not prescribe ophthalmic antibiotics simply because the eye is red.

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References

Centers for Disease Control and Prevention. (2021). Gonococcal infections among adolescents and adults. In Sexually transmitted infections treatment guidelines, 2021. https://www.cdc.gov/std/treatment-guidelines/gonorrhea-adults.htm

Hilaire, M. L., & Hornecker, J. R. (2026). Minor ophthalmic and otic disorders. In M. A. Chisholm-Burns, P. M. Malone, J. M. Kolesar, K. C. Lee, P. B. Bookstaver, & K. R. Matthias (Eds.), Pharmacotherapy principles & practice (7th ed.). McGraw Hill.

Yeu, E., & Hauswirth, S. (2020). A review of the differential diagnosis of acute infectious conjunctivitis: Implications for treatment and management. Clinical Ophthalmology, 14, 805–813. https://doi.org/10.2147/OPTH.S236571