Eye Anatomy and Causes of Red Eye

Overview of Eye Anatomy Relevant to Red Eye

• Conjunctiva: Covers the sclera ("white" of the eye) up to the edge of the cornea.
• Palpebral Conjunctiva: Lines the inside of the eyelids, normally transparent. Inflammation (conjunctivitis) causes redness and edema, obscuring the sclera.
• Sclera: The tough, white outer layer, forming about 5/6 of the eye's exterior.
• Cornea: A transparent, dome-shaped structure forming about 1/6 of the eye's surface. Highly sensitive due to its rich innervation
• Uveal Tract (Uvea): Made of the iris, ciliary body, and choroid; inflammation (uveitis) causes redness, pain, and photophobia.
• Eyelids and Lacrimal Apparatus: Issues with eyelids (blepharitis, styes, trauma) cause redness and irritation; lacrimal system problems cause tearing.

General Causes of Red Eye

• Red eye can result from various conditions, including conjunctival (conjunctivitis, subconjunctival hemorrhage), episcleral/scleral (episcleritis, scleritis), corneal (keratitis, abrasion, ulcer), uveal (uveitis, iritis), raised IOP (acute angle-closure glaucoma), intraocular infection, trauma, and other conditions (tumors, dry eyes).

Conjunctivitis (Most Common Cause)

• Viral Conjunctivitis: Often presents with watery discharge, flu-like symptoms, and palpebral conjunctiva follicles, particularly in the lower lid. Usually self-limiting within 1-2 weeks. Management is supportive (lubricants, hygiene).
• Adenoviral Keratoconjunctivitis: A more severe viral form with possible pseudomembrane formation and corneal involvement, requiring a short course of topical steroids under specialist supervision. High contagion is a factor in management.
• Bacterial Conjunctivitis: Presents with mucopurulent or purulent discharge (sticky eyelids), often worse on waking. Treatment includes broad-spectrum topical antibiotics (e.g., fluoroquinolones).
• Gonococcal/Chlamydial Conjunctivitis: Characterized by profuse purulent discharge and potential corneal involvement. Requires systemic antibiotic treatment (e.g., IM ceftriaxone) and management of any concomitant STIs.
• Allergic Conjunctivitis: Marked by intense itching, bilateral redness, watery discharge, and potentially significant inflammation, more pronounced in certain populations and environmental conditions. Treatment includes topical antihistamines and mast cell stabilizers.

Episcleritis & Scleritis

• Episcleritis: Mild inflammation, sectoral redness, commonly sectoral, and often resolves.
• Scleritis: Severe, often boring pain, no phenylephrine blanching, potential association with autoimmune disorders, requires systemic work-up and treatment with steroids, if necessary (can be vision-threatening).

Corneal Pathologies (Keratitis, Ulcers, Abrasions)

• Corneal Abrasion: Severe pain, photophobia, foreign-body sensation; fluorescein staining reveals epithelial defect. Management includes topical antibiotics, and potentially a bandage contact lens and cycloplegic for pain.
• Infectious Keratitis (Corneal Ulcer): Inflammation resulting from bacterial, viral, fungal or parasitic infections such as (Acanthamoeba), a serious complication that demands urgent management with topical antimicrobials.

Uveitis (Iritis, Iridocyclitis, Choroiditis)

• Inflammation of the uveal tract (iris, ciliary body, choroid). Signs include pain, photophobia, and a possible irregular pupil. Caused by autoimmune disorders, infections, or trauma. Management includes topical/systemic steroids and/or cycloplegics.

Acute Angle-Closure Glaucoma

• Sudden severe eye pain, nausea/vomiting, blurred vision, and a mid-dilated pupil. Characterised by elevated intraocular pressure (IOP). Urgent management includes decreasing IOP with medications like IV/oral acetazolamide, topical beta-blockers, alpha-agonists, and pilocarpine.

Endophthalmitis

• Infection within the eye (vitreous, aqueous). Presents with severe pain, profound vision loss, and marked redness. Management necessitates urgent referral and treatment with intravitreal antibiotics, possible vitrectomy.

Ocular Trauma

• Foreign Body/Abrasion: Check the cornea with fluorescein to confirm scratch. Remove foreign bodies if superficial; apply topical antibiotics.
• Penetrating Injury: Immediate treatment with protective shield, intravenous antibiotics, and urgent surgical repair are required.

Chemical Eye Injuries

• Immediate copious irrigation with balanced salt solutions to check the pH. Continue this until pH is normalized.

Tips

• The approach to assessing eye conditions should include visualization of the structures to the best of the observer's ability. Discharge is of importance, with considerations as to the nature and appearance of any discharge. Pain assessment provides considerable insight into the potential nature, severity and possible pathology of the conditions. If the patient reports intense pain, consider depth of pathology possibilities such as the potential of corneal involvement.