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Conjunctival Injection

What Is It, Causes, Diagnosis, and More

Author:Lily Guo

Editors:Ahaana Singh,Alyssa Haag,Emily Miao, PharmD

Illustrator:Jillian Dunbar

Copyeditor:David G. Walker


What is conjunctival injection?

Conjunctival injection, commonly referred to as blood shot eyes, describes the enlargement of the conjunctiva 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 (i.e., the 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. When conjunctival injection occurs, the eye may become irritated, and the individual may experience dryness, itching, and pain. 

What causes conjunctival injection?

Conjunctival injection is common and has many causes. The tiny blood vessels under the conjunctiva can become swollen because of environmental or lifestyle-related reasons, such as allergies leading to allergic conjunctivitis; 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 eye infections, such as conjunctivitis (i.e., inflammation of the conjunctiva), 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 mucus discharge.

Redness of the eye may also be a sign of a more serious eye condition or disease, such as uveitis (i.e., 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 conjunctiva injection include blepharitis, which is inflammation of the base of eyelashes 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 person 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, wearing contact lenses, or taking blood thinning medications (e.g., aspirin, warfarin). Keratitis, which is inflammation of the corneal epithelium caused by infection (e.g., herpes simplex virus, bacteria, fungi or protozoa), or auto-immune processes (e.g., collagen vascular diseases), can also result in conjunctival injection. 

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How is conjunctival injection diagnosed?

Conjunctival injection can be diagnosed by first obtaining a thorough and detailed patient history, assessing the onset and duration of symptoms, whether one or both eyes are affected, type and amount of discharge, any changes in vision, severity of pain, presence of allergies, and contact lens use. 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 opthamologist may be necessary if there is severe pain that does not resolve with topical anesthetics; if there is vision loss, which points to infectious keratitis and glaucoma; if there are large amounts of purulent discharge, which can indicate a bacterial infection; or if there has been a traumatic eye injury. An opthamologist may also be consulted if the pupils are fixed (i.e., unresponsive to light) or if the individual experiences a severe headache with nausea. Other signs that the red eye may be associated with a more serious condition include sensitivity to light or if the redness is present only in one eye.  

Ophthalmologists can conduct an examination with a slit lamp, which is an instrument that looks at 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 for rapid afferent pupillary defect, or function of the optic nerve in both eyes. In the penlight test, the examiner swings a light between both eyes, and the eye that the penlight is shone into should constrict. The other eye should also constrict, a process known as the consensual response. If there is damage to the optic nerve, the eye that was exposed to light will not constrict.

The physician may also put a drop of yellow 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 see 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. If the conjunctival injection has lasted for more than two to three weeks and has not resolved on its own or with home treatments, an eye culture may be performed, which occurs when a cotton swab is used to take a sample of cells from the inside of the eyelids. The sample is subsequently sent to a laboratory to be examined by a pathologist for the presence of bacteria or viruses. 

How is conjunctival injection treated?

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 two 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 for conjunctival injection and to reduce transmission if the cause is bacterial or viral. 

There is currently no specific diagnostic test to differentiate between bacterial and viral conjunctivitis; therefore, clinicians typically rely on a thorough history and physical examination. A bacterial cause may be suspected if there is a thick, purulent discharge coming from the eyes. On the other hand, a viral infection presents with a watery, mucus discharge with a burning and gritty feeling. Cases of bacterial conjunctivitis are usually treated with broad-spectrum antibiotics (e.g., fluoroquinolones) that are typically administered topically rather than orally to deliver high levels of the drugs directly to the site of infection. Examples may include erythromycin ointment, sulfacetamide drops, or polymyxin/trimethoprim eye drops. Cases of viral conjunctivitis are usually self-limiting and should resolve in 1-3 weeks, but if vision is affected or an individual experiences extreme sensitivity to light, a topical corticosteroid can be used. 

If the red eye occurs as a result of allergies, mild cases can be treated with over-the-counter antihistamine/vasoconstrictor agents (e.g., cetirizine, fexofenadine, and loratadine) or with a second-generation topical histamine H1 receptor antagonist (e.g., alcaftadine). Those with chronic blepharitis, or eyelid inflammation, may benefit from oral antibiotics, such as tetracycline or doxycycline.

What are the most important facts to know about conjunctival injection?

Conjunctival injection is a common condition that refers to the inflammation and dilation of blood vessels of the eye that supply the conjunctiva. The conjunctiva is a thin membrane that covers the surface of the eye and the inner eyelids; it serves to lubricate the eye and provide protection from environmental factors. There are many causes of conjunctival injection, some benign and others more serious. Lifestyle factors, such as eye strain from prolonged reading, allergies, or exposure to chemicals in a swimming pool, can cause benign conjunctival injection. More serious conditions that can result in red eye include glaucoma, keratitis, or blepharitis. A thorough patient history followed by a physical exam can help diagnose conjunctival injection. An ophthalmologist may also choose to examine the eye using a slit lamp or fluorescein dye to detect any damage to the cornea. Treatment may not be necessary if the red eye is self resolving; however, if there are signs of bacterial infection, antibiotics may be prescribed. 

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Related links

Conjunctivitis
Glaucoma
Anatomy and Physiology of the Eye
Uveitis
Keratitis

Resources for research and reference

Centers for Disease Control and Prevention. (2019, January 4). Signs and symptoms of pink eye (conjunctivitis). In Centers for Disease Control and Prevention. Retrieved September 18, 2021, from https://www.cdc.gov/conjunctivitis/about/symptoms.html 

Cronau, H., Kankanala, R. R., & Mauger, T. (2010, January 15). Diagnosis and management of red eye in primary care. In American Family Physician. Retrieved September 18, 2021, from https://www.aafp.org/afp/2010/0115/p137.html 

Diagnosing conjunctivitis. In Patient Care at NYU Langone Health. Retrieved September 18, 2021, from https://nyulangone.org/conditions/conjunctivitis/diagnosis#:~:text=Most%20of%20the%20time%2C%20your,of%20light%20into%20your%20eye 

Heiting, G. (2021, September 7). Conjunctiva of the eye. In All About Vision. Retrieved September 18, 2021, from https://www.allaboutvision.com/resources/conjunctiva.htm 

Heiting, G. (2021, September 7). Red eyes (bloodshot eyes): Causes and treatments. In All About Vision. Retrieved September 18, 2021, from https://www.allaboutvision.com/conditions/red-eyes.htm 

Mayo Foundation for Medical Education and Research. (2020, June 13). Uveitis. In Mayo Clinic. Retrieved September 18, 2021, from https://www.mayoclinic.org/diseases-conditions/uveitis/symptoms-causes/syc-20378734

Park, I. K., Chun, Y. S., Kim, K. G., Yang, H. K., & Hwang, J-M. (2013, August 1). New clinical grading scales and objective measurement for Conjunctival Injection. In Investigative Ophthalmology & Visual Science. Retrieved September 18, 2021, from https://iovs.arvojournals.org/article.aspx?articleid=2127854 

Roat, M.I. (2021). Viral Conjunctivitis. In Merck Manuals Professional Edition. Retrieved September 29, 2021, from https://www.merckmanuals.com/professional/eye-disorders/conjunctival-and-scleral-disorders/viral-conjunctivitis

Subconjunctival Hemorrhage: Symptoms, Causes, Treatments. In Cleveland Clinic. Retrieved September 18, 2021, from https://my.clevelandclinic.org/health/diseases/17713-subconjunctival-hemorrhage