What is Conjunctival Injection?
Conjunctival injection is the dilation and engorgement of the blood vessels in the conjunctiva, resulting in the characteristic "red eye" appearance.
Definition and Clinical Significance
Conjunctival injection refers specifically to the redness caused by dilation of the posterior conjunctival blood vessels 1. This is a cardinal sign of ocular inflammation and represents one of the most common presenting complaints in ophthalmology 2.
Critical Distinction: Conjunctival vs. Ciliary Injection
The most important clinical differentiation is between conjunctival injection and ciliary injection 1:
Conjunctival injection: Affects the superficial, posterior conjunctival vessels. The redness is more prominent in the periphery (away from the cornea) and blanches with topical vasoconstrictors. Generally indicates less serious conditions like conjunctivitis.
Ciliary injection: Indicates inflammation of deeper structures (cornea, iris, or ciliary body). The redness forms a violaceous ring around the cornea (limbus) and does not blanch with vasoconstrictors. This pattern demands urgent ophthalmologic consultation 1.
Clinical Patterns and Presentations
Conjunctival injection appears across virtually all forms of conjunctivitis described in the 2024 guidelines 2:
Infectious Causes
- Viral (adenoviral): Bulbar conjunctival injection with watery discharge and follicular reaction
- Bacterial (gonococcal): Marked bulbar conjunctival injection with purulent discharge
- Chlamydial: Bulbar conjunctival injection with follicular conjunctivitis
- HSV/VZV: Unilateral bulbar conjunctival injection with watery discharge
Immune-Mediated Causes
- Stevens-Johnson syndrome/TEN: Bilateral bulbar conjunctival injection with membrane formation
- GVHD: Bilateral conjunctival injection with chemosis
- Vasculitis: Variable presentation with conjunctival nodules or granulomas
Other Causes
- Mucus fishing syndrome: Conjunctival injection with excessive mucus production from mechanical trauma
- COVID-19: Unilateral more than bilateral conjunctival injection, typically mild and self-limited 2
Common Pitfall
Do not confuse simple conjunctival injection (benign) with ciliary injection (serious). The latter requires same-day ophthalmology referral as it suggests corneal ulcer, acute angle-closure glaucoma, iritis, or other vision-threatening conditions 1.