Keratitis vs Conjunctivitis: Key Differences
In a patient with unilateral eye pain, redness, no discharge, and punctate fluorescein uptake on the cornea, this presentation is consistent with keratitis, not conjunctivitis—the corneal involvement with fluorescein uptake is the critical distinguishing feature that demands urgent ophthalmologic evaluation.
Anatomic Location: The Fundamental Distinction
Keratitis involves inflammation of the cornea (the clear, dome-shaped surface covering the front of the eye), while conjunctivitis primarily affects the conjunctiva (the thin, transparent membrane covering the white part of the eye and inner eyelids) 1.
Clinical Presentation Differences
Keratitis Characteristics:
- Severe pain that is disproportionate to findings
- Photophobia (light sensitivity)
- Vision impairment or blurred vision
- Corneal involvement visible on examination:
- Punctate fluorescein staining (as in your patient)
- Corneal infiltrates or ulceration
- Stromal involvement
- Epithelial defects 2
- Typically unilateral
- Minimal to no discharge
- Ciliary flush (redness concentrated around the cornea)
Conjunctivitis Characteristics:
- Mild to moderate discomfort (foreign body sensation, itching)
- Discharge is common:
- Watery (viral)
- Purulent (bacterial)
- Mucoid (allergic)
- Conjunctival injection (diffuse redness)
- Normal vision typically preserved
- No corneal involvement on fluorescein staining (though viral conjunctivitis can secondarily cause keratitis) 1
- Often bilateral (especially viral and allergic types)
- Follicular or papillary reaction on tarsal conjunctiva 1
Urgency and Prognosis
Keratitis: Vision-Threatening Emergency
Bacterial keratitis can cause rapid tissue destruction within 24 hours, potentially leading to 2:
- Corneal scarring and permanent vision loss
- Corneal perforation
- Endophthalmitis
- Loss of the eye
Immediate ophthalmologic referral is mandatory for any patient with suspected keratitis 3.
Conjunctivitis: Generally Self-Limited
Most conjunctivitis cases resolve spontaneously within 5-14 days without serious sequelae 1. Referral is indicated only if:
- No improvement after 10 days of treatment
- Severe pain or vision loss develops
- Corneal involvement occurs 4, 3
Your Patient's Presentation
The combination of:
- Unilateral presentation
- Eye pain (not just irritation)
- No discharge
- Punctate fluorescein uptake on cornea
This definitively indicates keratitis, not conjunctivitis 2, 3. The fluorescein uptake demonstrates corneal epithelial disruption, which is the hallmark of keratitis.
Critical Pitfalls to Avoid
Never prescribe topical corticosteroids for red eye in primary care without ophthalmologic evaluation—they can worsen infectious keratitis and cause corneal perforation 4
Never use topical anesthetics for treatment (only for examination)—they inhibit corneal healing 4
Do not delay referral waiting for culture results—bacterial keratitis requires immediate empiric treatment 2
Fluorescein staining belongs in ophthalmology for diagnostic purposes in primary care settings 4—if you see corneal uptake, refer immediately
Risk Factors Distinguishing the Conditions
Keratitis Risk Factors 2:
- Contact lens wear (especially overnight wear, tap water exposure)
- Corneal trauma or foreign body
- Previous corneal surgery
- Dry eye disease
- Immunocompromise
- Topical corticosteroid use
Conjunctivitis Risk Factors 1:
- Viral exposure (schools, healthcare settings)
- Allergies
- Contact lens wear (giant papillary conjunctivitis)
- Blepharitis
- Dry eye (secondary conjunctival inflammation)
Bottom line: Corneal involvement with pain and fluorescein uptake = keratitis = urgent ophthalmology referral. Conjunctival redness with discharge and no corneal findings = conjunctivitis = can often be managed in primary care.