Conjunctival Injection · What Is It, Causes, Diagnosis, and More

Conjunctival injection, commonly referred to as bloodshot eyes, describes the enlargement of the conjunctiva’s blood vessels. The conjunctiva, which is the mucous membrane that covers the surface of the eyeball and lines the inner eyelids, has two segments: the bulbar conjunctiva, which covers the anterior portion of the sclera, or white of the eye; and the palpebral conjunctiva, which covers the inner surface of the upper and lower eyelids. The function of the conjunctiva is to lubricate the eye and protect it from dust, debris, and infection-causing microorganisms. Conjunctival injection often occurs with eye irritation, and the individual may experience dryness, itching, and pain.  

Conjunctival injection is common and has many causes. The tiny blood vessels under the conjunctiva can become swollen due to allergies leading to allergic conjunctivitis, which is when the conjunctiva is inflamed; eye fatigue from prolonged reading, writing, or driving; chemical irritation, such as chlorine from swimming pools; and wearing contact lenses for too long.  

Oftentimes, conjunctival injection can result from infectious conjunctivitis, commonly known as pink eye. Pink eye can occur due to a bacterial or viral infection and is characterized by redness, a gritty sensation in the eye, and itching. Bacterial conjunctivitis often causes a purulent discharge to form, resulting in the formation of crust on the eyelashes. Viral conjunctivitis, on the other hand, typically produces a watery discharge. 

Conjunctival injection may also be a sign of a more serious eye condition or disease, such as uveitis, which is inflammation of the uvea, or the middle layer of the eye. It may also be a sign of glaucoma, an ocular disease in which the aqueous humor is unable to drain, resulting in increased pressure of the eye, compression of the optic nerve, and an increased risk for blindness.  

Other causes of conjunctival injection include blepharitis, which is inflammation of the eyelids typically caused by a Staphylococcal aureus infection; corneal abrasion; corneal ulcers; a foreign body in the eye; or subconjunctival hemorrhage, which refers to rupture of the blood vessels in the conjunctiva. A subconjunctival hemorrhage can occur if the individual has been straining, like during coughing, sneezing, vomiting, or defecating. Subconjunctival hemorrhage may also be caused by injury to the head or eye, infection, repeated and forceful rubbing of the eye, or wearing contact lenses. Those taking blood thinning medications such as aspirin and warfarin are more susceptible to subconjunctival hemorrhage.  

Lastly, keratitis, which is inflammation of the cornea caused by infection (e.g., herpes simplex virus, bacteria, fungi, or protozoa), or autoimmune processes (e.g., collagen vascular diseases), can also result in conjunctival injection.  

Conjunctival injection can be diagnosed clinically using history and physical examination. A physical examination will typically involve assessment of the eyelids and lacrimal, or tear, sac; pupil size and their reaction to light; corneal involvement; and the pattern and location of the red eye. Visual acuity and involvement of the surrounding lymph nodes should also be examined. Referral to an ophthalmologist may be necessary if there is severe pain; if there is vision loss, which points to infectious keratitis or glaucoma; if there are large amounts of purulent discharge; or if there has been a traumatic eye injury. An ophthalmologist may also be consulted if the pupils are fixed (i.e., unresponsive to light) or if the individual experiences a severe headache with nausea.  

Ophthalmologists can conduct an examination with a slit lamp, which is an instrument that visualizes the structures of the eye using a microscope and a high-energy beam of light, and a tonometer, which measures intraocular pressure. A penlight test, also known as a swinging light test, can be used to assess optic nerve function. In the penlight test, the examiner swings a light between both eyes, and the eye that light is shone into should constrict. The other eye should also constrict equally, a process known as consensual response. If there is damage to the optic nerve or anywhere along the optic tract, the eyes will not constrict appropriately to light. 

The clinician may also place a drop of dye called fluorescein in the eye, which allows for a more detailed look at any damage on the surface of the eye. A visual acuity test may also be performed to assess if vision has been affected. This involves testing the individual's ability to read letters or symbols from 20 feet away while covering one eye at a time. An eye culture may be performed if an infectious process is suspected and involves using a cotton swab to take a sample of cells from the inside of the eyelids.  

Treatment of conjunctival injection involves treating the underlying cause. If the conjunctival injection is due to hemorrhage of the vessels, treatment is oftentimes not necessary as broken vessels heal within 2 weeks. Eye drops containing artificial tears and lubricants may be used in the management of red eye if the symptoms are due to dryness. Contact lens wearers, especially those who use extended wear lenses, should consider using glasses to minimize irritation on the eye surface.  

Good hygiene and meticulous hand washing are advised as preventative measures and to reduce transmission for infectious conjunctivitis. Bacterial conjunctivitis is usually treated with topical antibiotics administered as ointments or eye drops. Examples include erythromycin ointment, ciprofloxacin, or polymyxin/trimethoprim eye drops. Cases of viral conjunctivitis are usually self-limiting and should resolve in 1-3 weeks, but if symptoms are severe, topical antivirals such as acyclovir ointment may be prescribed.  

Mild cases of conjunctival injection from allergies can be treated with over-the-counter topical antihistamines like alcaftadine eye drops or oral antihistamines like cetirizine, fexofenadine, and loratadine. Those with chronic blepharitis are advised to maintain good eyelid hygiene and attempt to eliminate triggers, like limiting eye makeup use). Additionally, individuals can use warm compresses to alleviate symptoms.