What is the differential diagnosis and treatment for a patient presenting with eye pain and redness, considering potential causes such as conjunctivitis, keratitis, uveitis, and angle-closure glaucoma?

Differential Diagnosis for Eye Pain and Redness

Immediate Sight-Threatening Emergencies to Rule Out First

Acute angle-closure glaucoma is the most critical diagnosis to exclude immediately, as untreated eyes can become blind within hours and 18% become permanently blind within 4-10 years. 1, 2 Look for sudden severe pain, mid-dilated fixed pupil, "steamy" corneal appearance, markedly elevated intraocular pressure (>40 mmHg), nausea/vomiting, and halos around lights. 1, 2

Red Flags Requiring Emergency Ophthalmology Referral

• Vision loss or acute visual changes 1
• Severe pain not relieved by topical anesthetics 3
• Mid-dilated, asymmetric, or distorted pupil (suggests angle-closure) 1, 2
• Corneal involvement (stromal infiltrates, edema, or epithelial defects) 4, 1
• Recent ocular surgery or traumatic eye injury 1, 3
• Signs of herpes infection (unilateral presentation with dendritic lesions) 1, 3

Algorithmic Diagnostic Approach

Step 1: Assess Pain Severity and Vision

If severe pain with vision loss: Measure IOP immediately and assess pupil reactivity. 2, 5

• IOP >40 mmHg + mid-dilated pupil + corneal edema = Acute angle-closure glaucoma - treat immediately with topical beta-blockers, alpha-2 agonists, carbonic anhydrase inhibitors, and oral/IV hyperosmotic agents, then emergent laser peripheral iridotomy. 2
• Normal IOP + photophobia + cells/flare in anterior chamber = Anterior uveitis - presents with dull aching pain and small pupil (differentiates from glaucoma). 4, 2

Step 2: Examine for Corneal Pathology

Use fluorescein staining to identify epithelial defects. 4, 6

• Suppurative stromal infiltrates >1mm with indistinct edges + epithelial defect = Bacterial keratitis - requires immediate empiric broad-spectrum topical antibiotics as destruction can occur within 24 hours with virulent organisms (Pseudomonas, Streptococcus pneumoniae, Neisseria gonorrhoeae). 4, 1 Contact lens wear, overnight wear, tap-water rinsing, or swimming with lenses are key risk factors. 4

• Epithelial defect without stromal infiltrates = Corneal abrasion - stromal infiltrates distinguish bacterial keratitis from simple abrasion. 1, 2

• Unilateral presentation with dendritic lesions = Herpes simplex keratitis - treat with topical ganciclovir 0.15% gel 3-5 times daily or trifluridine 1% solution 5-8 times daily, plus oral antivirals (acyclovir 200-400mg 5x/day, valacyclovir 500mg 2-3x/day, or famciclovir 250mg twice daily). 4, 1

Step 3: Differentiate Conjunctivitis Types

Presence of itching strongly suggests allergic etiology. 1

• Matter/crusting on waking = Bacterial conjunctivitis - typically self-limited but can treat with broad-spectrum topical antibiotics. 1, 3

• Watery discharge + preauricular lymphadenopathy = Viral conjunctivitis - self-limited, resolves in 10-14 days, does not respond to antibacterial agents. 1, 3 For severe adenoviral keratoconjunctivitis with marked chemosis, lid swelling, or membranous conjunctivitis, topical corticosteroids reduce symptoms and scarring, but require close follow-up for IOP monitoring. 4

Step 4: Consider Other Causes

• Deep boring pain worse at night + violaceous hue = Scleritis - may radiate to face. 2

• Sectoral redness + milder discomfort = Episcleritis 2

• Irritation, burning, intermittent blurred vision with inconsistent clinical signs = Dry eye syndrome 1

• Eyelid margin inflammation = Blepharitis/meibomian gland dysfunction - treat the underlying eyelid problem rather than just conjunctival symptoms. 1

Critical Pitfalls to Avoid

Never patch an eye with suspected infection or in contact lens wearers. 1

Never use topical corticosteroids until organism is identified and infection is responding to therapy in bacterial keratitis. 1 However, corticosteroids are appropriate for severe viral conjunctivitis with membranous changes or for herpes simplex stromal keratitis when combined with oral antivirals. 4

Do not dilate pupils in patients with suspected narrow angles or intermittent angle-closure symptoms until after laser peripheral iridotomy is performed, as dilation can precipitate acute crisis. 2

Avoid indiscriminate topical antibiotics - viral conjunctivitis will not respond and mild bacterial conjunctivitis is often self-limited. 1

Do not dismiss transient symptoms as benign - intermittent episodes are warning signs before potentially blinding acute attacks in angle-closure glaucoma. 2

Topical trifluridine inevitably causes epithelial toxicity if used for more than 2 weeks. 4

When to Refer vs. Manage in Primary Care

Immediate ophthalmology referral required for: 1, 5, 3

• Any vision-threatening condition (angle-closure glaucoma, bacterial keratitis, uveitis)
• Corneal involvement with stromal infiltrates
• Need for topical corticosteroids
• Severe pain or photophobia with blurred vision
• Copious purulent discharge
• Recurrent infections

Can manage in primary care: 3

• Mild viral or bacterial conjunctivitis without vision changes
• Simple conjunctival injection without corneal involvement
• Allergic conjunctivitis
• Mild blepharitis

Refer if no improvement after 10 days of treatment. 6