Red Eye: What You Need to Know About Conjunctival and Corneal Problems

Red eye is a common symptom that can have various causes and presentations. It can range from mild and self-limiting to severe and sight threatening. Therefore, it is important for health care providers to be able to recognise and manage the different causes of red eye, and to refer appropriately when needed.

In this article, we will focus on two categories of red eye causes: conjunctival causes and corneal conditions.

Conjunctival causes

The conjunctiva is the thin membrane that covers the white part of the eye and the inner surface of the eyelids. It can become inflamed or infected by various agents, leading to conjunctivitis, which is also known as pink eye.

Conjunctivitis can be caused by:

• Viral infections, such as adenovirus, herpes simplex, or varicella-zoster. Viral conjunctivitis typically affects one eye first, then spreads to the other eye within a few days. It is often associated with upper respiratory tract symptoms, such as sore throat, cough, or fever. It may also cause watery discharge, itching, burning, or foreign body sensation in the eye.
• Bacterial infections, such as Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, or Chlamydia trachomatis. Bacterial conjunctivitis usually affects both eyes at the same time. It may cause purulent discharge, crusting of the eyelids, or eyelash loss.
• Allergic reactions, such as to pollen, dust mites, animal dander, or cosmetics. Allergic conjunctivitis often affects both eyes simultaneously. It may cause itching, tearing, redness, or swelling of the eyes or eyelids.
• Irritants, such as smoke, chlorine, or contact lenses. Irritant conjunctivitis can affect one or both eyes depending on the exposure. It may cause redness, burning, tearing, or foreign body sensation in the eye.

Conjunctivitis is usually diagnosed by history and examination. Treatment depends on the cause and severity of the condition. Viral conjunctivitis is usually self-limiting and requires supportive care, such as artificial tears, cold compresses, or antihistamines. Bacterial conjunctivitis may require topical antibiotics, such as chloramphenicol or fusidic acid. Allergic conjunctivitis may respond to topical antihistamines, mast cell stabilisers, or corticosteroids. Irritant conjunctivitis may improve by avoiding or removing the offending agent and using lubricating drops.

Conjunctivitis is usually benign and does not affect vision. However, some complications that may warrant referral include:

• Keratitis (inflammation of the cornea), which can cause pain, photophobia (sensitivity to light), blurred vision, or corneal ulceration.
• Uveitis (inflammation of the uvea), which can cause pain, photophobia (sensitivity to light), blurred vision, or glaucoma (increased pressure in the eye)¹.
• Preseptal cellulitis (infection of the eyelid), which can cause pain, swelling, erythema (redness), or fever.
• Orbital cellulitis (infection of the orbit), which can cause pain, proptosis (bulging of the eye), ophthalmoplegia (paralysis of eye movements), or vision loss.

Corneal conditions

The cornea is the transparent layer that covers the front of the eye. It can be damaged by various factors, leading to corneal abrasion (scratch), ulcer (infection), erosion (recurrent abrasion), dystrophy (degeneration), or keratitis (inflammation).

Corneal conditions can be caused by:

• Trauma, such as from a foreign body (e.g., dust, metal), contact lens wear (e.g., overuse, poor hygiene, improper fit), or eye injury (e.g., scratch, burn, chemical).
• Infection, such as from bacteria (e.g., Pseudomonas, Staphylococcus), viruses (e.g., herpes simplex, varicella-zoster), fungi (e.g., Candida, Aspergillus), or parasites (e.g., Acanthamoeba, microsporidia).
• Inflammation, such as from autoimmune diseases (e.g., rheumatoid arthritis, Sjögren’s syndrome), allergic reactions (e.g., vernal keratoconjunctivitis, atopic keratoconjunctivitis), or dry eye syndrome (e.g., due to aging, medications, environmental factors).
• Degeneration, such as from genetic disorders (e.g., Fuchs’ dystrophy, keratoconus), metabolic disorders (e.g., diabetes mellitus, gout), or aging (e.g., arcus senilis, corneal oedema).

Corneal conditions are usually diagnosed by history and examination. Treatment depends on the cause and severity of the condition. Traumatic corneal abrasions may require topical antibiotics, analgesics, or cycloplegics. Infectious corneal ulcers may require topical or systemic antimicrobials. Inflammatory corneal erosions may require topical lubricants, corticosteroids, or immunosuppressants. Degenerative corneal dystrophies may require surgical interventions, such as corneal transplantation or cross-linking.

Corneal conditions can affect vision and cause complications, such as:

• Scarring (opacity of the cornea)
• Neovascularization (growth of new blood vessels in the cornea)
• Perforation (rupture of the cornea)
• Endophthalmitis (infection of the inside of the eye)
• Glaucoma (increased pressure in the eye)

Therefore, some indications for referral include:

• Severe pain or photophobia
• Reduced visual acuity.
• Large or deep corneal defect
• Suspected microbial keratitis.
• Corneal involvement in ocular herpes
• Corneal thinning or perforation
• Recurrent corneal erosion
• Progressive corneal dystrophy

In conclusion, conjunctival causes and corneal conditions are two common categories of red eye causes that health care providers should be familiar with. They can have different causes, symptoms, treatments, and complications. It is important to recognise and manage them appropriately and to refer when needed.

 If you are interested in learning more about the common causes of red eye and how to manage them effectively, you may want to consider enrolling in the Minor ailments: ear and eye conditions for the primary care practitioners course offered by Practitioner Development UK. This course is designed to help you enhance your knowledge and skills in assessing and treating minor ear and eye problems in primary care settings. 

You will learn about the anatomy, physiology, and pathology of the ear and eye, the common presentations and differential diagnoses of ear and eye conditions, the evidence-based management and referral criteria for ear and eye problems. The course is delivered by experienced clinicians and educators and is suitable for nurses, pharmacists, paramedics, physician associates, and other health care professionals who work in primary care settings. 

References:

 Red and Bloodshot Eyes: Common Causes, Treatment - WebMD. (2021, October 19). Retrieved from https://www.webmd.com/eye-health/why-eyes-red

Red Eye: Causes, Treatment & Prevention - Cleveland Clinic. (2020, July 16). Retrieved from https://my.clevelandclinic.org/health/symptoms/17690-red-eye

Red eye | Specsavers Australia. (n.d.). Retrieved from https://www.specsavers.com.au/eye-health/eye-conditions/red-eye

Red Eyes: 20 Causes, Symptoms, Complications, and More - Healthline. (2019, March 7). Retrieved from https://www.healthline.com/health/eye-redness

Red eye Causes - Mayo Clinic. (n.d.). Retrieved from https://www.mayoclinic.org/symptoms/red-eye/basics/causes/sym-20050748