Red eye, or ocular redness, is a common presenting complaint in ophthalmology and primary care settings. It refers to the visible inflammation or congestion of the conjunctival blood vessels, resulting in a reddish appearance of the white part of the eye (sclera). While often benign and self-limiting, red eye can also be a symptom of serious underlying ocular or systemic conditions that require prompt diagnosis and treatment. Therefore, a systematic approach to the Differential Diagnosis Of Red Eye is crucial for effective patient management and prevention of potential vision-threatening complications.
Common Causes of Red Eye
Several conditions can manifest as red eye, ranging from mild irritations to sight-threatening emergencies. Understanding the distinguishing features of each condition is essential for accurate differential diagnosis.
Conjunctivitis
Conjunctivitis, or inflammation of the conjunctiva, is one of the most frequent causes of red eye. It can be broadly classified into infectious and non-infectious types.
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Infectious Conjunctivitis: This is commonly caused by viruses (adenovirus being the most common), bacteria (such as Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae), or, less frequently, chlamydia or gonorrhea. Viral conjunctivitis is often associated with watery discharge, a gritty sensation, and may be accompanied by upper respiratory tract infection symptoms. Bacterial conjunctivitis typically presents with purulent discharge, matted eyelashes upon awakening, and a more pronounced redness.
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Allergic Conjunctivitis: This is triggered by allergens such as pollen, dust mites, or pet dander. It is characterized by intense itching, watery discharge, and often bilateral involvement. Patients may also report a history of allergies or atopic conditions.
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Chemical and Irritant Conjunctivitis: Exposure to chemicals (acids, alkalis), smoke, or other irritants can cause conjunctival inflammation. The history of exposure is crucial in these cases. Symptoms can range from mild redness and tearing to severe pain and potential corneal damage depending on the nature and duration of exposure.
Corneal Abrasion and Foreign Body
Trauma to the cornea, whether from a scratch, contact lens overwear, or a foreign body, is another common cause of red eye. Corneal abrasions are often intensely painful, with a sensation of something being in the eye (foreign body sensation), tearing, and photophobia. A careful history and examination, sometimes with fluorescein staining, can help identify corneal abrasions and rule out retained foreign bodies.
Dry Eye Syndrome
Dry eye syndrome, or keratoconjunctivitis sicca, is a chronic condition characterized by insufficient tear production or poor tear quality. While not always presenting with prominent redness, chronic dry eye can lead to intermittent or persistent mild red eye, along with symptoms of dryness, burning, grittiness, and fluctuating vision.
Subconjunctival Hemorrhage
Subconjunctival hemorrhage occurs when a small blood vessel beneath the conjunctiva ruptures, leading to a dramatic, localized red patch on the sclera. It can be spontaneous, occur after minor trauma (rubbing the eye, coughing, sneezing), or be associated with blood thinning medications. While alarming in appearance, subconjunctival hemorrhage is usually painless, does not affect vision, and resolves spontaneously within a few weeks.
Serious Causes of Red Eye
While many causes of red eye are benign, some conditions require urgent attention due to their potential to cause vision loss or indicate systemic disease.
Acute Angle-Closure Glaucoma
Acute angle-closure glaucoma is a medical emergency characterized by a sudden and rapid increase in intraocular pressure. It presents with severe eye pain, headache, blurred vision, halos around lights, nausea, and vomiting. The eye is typically intensely red, with a hazy cornea and a fixed, mid-dilated pupil. Prompt diagnosis and treatment are crucial to prevent irreversible optic nerve damage and vision loss.
Uveitis
Uveitis refers to inflammation of the uveal tract, which includes the iris, ciliary body, and choroid. Anterior uveitis (iritis) is the most common form and can present with red eye, moderate pain, photophobia, and blurred vision. Slit-lamp examination may reveal cells and flare in the anterior chamber. Uveitis can be associated with systemic inflammatory conditions or infections and requires ophthalmologic evaluation to determine the underlying cause and initiate appropriate treatment.
Keratitis
Keratitis, or inflammation of the cornea, can be infectious (bacterial, viral, fungal, or amoebic) or non-infectious (e.g., exposure keratitis, contact lens-related). Infectious keratitis, particularly bacterial and amoebic keratitis, can be sight-threatening and requires urgent diagnosis and management. Symptoms include red eye, severe pain, photophobia, blurred vision, and tearing. Corneal examination may reveal an infiltrate or ulcer.
Orbital Cellulitis
Orbital cellulitis is an infection of the tissues surrounding the eye, posterior to the orbital septum. It is a serious condition that can spread to the brain and cause significant morbidity. Symptoms include red eye, eyelid swelling, proptosis (bulging of the eye), pain with eye movements, decreased vision, and fever. Orbital cellulitis typically requires intravenous antibiotics and may necessitate surgical drainage in some cases.
Diagnostic Approach to Red Eye
The differential diagnosis of red eye relies on a thorough history and physical examination. Key elements include:
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History: Detailed questioning about the onset, duration, and characteristics of symptoms (pain, itching, discharge, vision changes, photophobia, foreign body sensation). History of trauma, contact lens wear, allergies, systemic diseases, and medications should also be elicited.
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Visual Acuity Assessment: Checking visual acuity is crucial to identify vision-threatening conditions. A significant decrease in visual acuity warrants prompt ophthalmologic referral.
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Pupillary Examination: Assessing pupillary size, shape, and reactivity to light is important. An abnormal pupil, such as a fixed or dilated pupil, may suggest acute angle-closure glaucoma or uveitis.
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Slit-Lamp Examination: Slit-lamp biomicroscopy allows for detailed examination of the conjunctiva, cornea, anterior chamber, and iris. It helps in identifying corneal abrasions, foreign bodies, conjunctival discharge, anterior chamber cells and flare (uveitis), and corneal infiltrates (keratitis).
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Intraocular Pressure Measurement: Tonometry is essential in cases of red eye with pain to rule out acute angle-closure glaucoma.
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Eyelid and Orbital Examination: Palpation of the eyelids and periorbital tissues can help detect signs of orbital cellulitis or other periocular infections.
Conclusion
Red eye is a common and often self-limiting condition. However, it can also be a sign of serious ocular or systemic disease. A systematic approach to differential diagnosis, based on careful history taking and thorough eye examination, is crucial for accurate diagnosis and timely management. Patients with red eye accompanied by significant pain, vision changes, photophobia, or abnormal pupillary responses should be promptly evaluated by an ophthalmologist to rule out sight-threatening conditions and receive appropriate care.
