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Infectious Diseases and Microbiology: Red Eye
Basics
Description
Red eye may result from sight-threatening conditions such as uveitis, endophthalmitis, acute angle-closure glaucoma, or scleritis, which typically produce ciliary injection. More commonly, redness is due to conjunctival hyperemia associated with conjunctivitis, keratitis, dry eye disease, foreign body irritation (including contact lenses), blepharitis, or environmental irritants. Ocular trauma may cause subconjunctival hemorrhage. Not all causes are infectious. Uveitis involves intraocular inflammation and may be anterior, posterior, or pan-uveitis. Endophthalmitis is a severe intraocular infection involving the vitreous cavity. Acute angle-closure glaucoma is an ophthalmic emergency caused by obstruction of aqueous outflow and elevated intraocular pressure. Episcleritis affects superficial scleral tissues, while scleritis is a deeper, more severe inflammatory process that may occur with keratitis or uveitis. Conjunctivitis is the most common cause of red eye and usually includes discharge. Keratitis primarily affects the cornea.
Epidemiology
Primary acute angle closure occurs more frequently in Asian populations than in Caucasians. Incidence rates for conjunctivitis, keratitis, and uveitis vary and are addressed in their respective discussions.
Risk Factors
Risk factors for angle-closure glaucoma include advanced age, hyperopia, cataract, female sex, prior angle closure in the fellow eye, and Asian ethnicity; prophylactic laser iridotomy is often performed in the unaffected eye. Contact lens use increases the risk of bacterial keratitis. Subconjunctival hemorrhage may occur spontaneously or with bleeding disorders, minor trauma, or increased venous pressure from coughing or sneezing. Autoimmune connective tissue disorders are associated with ocular inflammation, and uveitis may be an initial manifestation.
General Prevention
Proper contact lens hygiene reduces infectious and inflammatory complications. Screening with gonioscopy and preventive laser iridotomy can prevent acute angle closure in high-risk individuals.
Pathophysiology
Ciliary injection involves deeper vascular branches and indicates inflammation of the cornea, iris, ciliary body, or sclera. Conjunctival injection is superficial, mobile with the conjunctiva, and improves with topical vasoconstrictors. Acute angle closure usually results from pupillary block, causing pressure differential between the posterior and anterior chambers, forward bowing of the iris, and obstruction of aqueous outflow through the trabecular meshwork.
Etiology
Conjunctivitis, keratitis, uveitis, and endophthalmitis have infectious and noninfectious causes. Acute angle-closure glaucoma and subconjunctival hemorrhage are noninfectious. Episcleritis is usually idiopathic, though immunologic reactions to herpes simplex or varicella zoster may occur. Scleritis is rarely infectious but may result from systemic infections or extension from keratitis; reported pathogens include fungi (Aspergillus, Fusarium), herpes viruses, mycobacteria, Nocardia, Pseudomonas, Proteus (after scleral buckle procedures), syphilis, leprosy, Lyme disease, and tuberculosis.
Commonly Associated Conditions
Endophthalmitis most commonly follows intraocular surgery. Contact lens wear strongly predisposes to bacterial keratitis.
Diagnosis
History
Subconjunctival hemorrhage is unilateral, painless, and vision is unaffected. Conjunctivitis often begins in one eye but is commonly bilateral and features discharge with minimal visual change. Keratitis is usually unilateral and associated with redness, foreign body sensation, tearing, and decreased vision. Uveitis presents with reduced vision, photophobia, and ocular pain. Acute angle-closure glaucoma presents with severe unilateral pain, decreased vision, nausea, and vomiting. Anterior scleritis causes severe pain and tenderness; posterior scleritis may cause significant visual impairment with less obvious redness. Episcleritis resembles conjunctivitis but has mild discomfort and no discharge. Endophthalmitis presents with pain and significant vision loss.
Physical Examination
Slit-lamp examination is essential. Subconjunctival hemorrhage appears as a sharply demarcated red patch under the conjunctiva. Conjunctivitis shows hyperemia, discharge, membranes or pseudomembranes, papillary or follicular reaction, and possibly preauricular lymphadenopathy. Keratitis reveals epithelial defects, stromal opacities, discharge, and anterior chamber inflammation. Anterior uveitis is diagnosed by inflammatory cells in the anterior chamber and keratic precipitates. Acute angle closure presents with a mid-dilated poorly reactive pupil, corneal edema, and elevated intraocular pressure.
Diagnostic Tests and Interpretation
Laboratory Studies
Routine cultures are unnecessary in typical conjunctivitis except in hyperacute cases suggestive of Neisseria gonorrhoeae. Keratitis lesions are sampled for Gram stain and culture.
Imaging
Confocal microscopy assists in diagnosing Acanthamoeba keratitis. Neuroimaging may identify vascular abnormalities such as carotid-cavernous fistulas or arteriovenous malformations associated with red eye.
Diagnostic Procedures/Other
Corneal biopsy may be needed for refractory keratitis. Vitreous sampling during vitrectomy can assist in diagnosing uveitis or endophthalmitis via cytology, culture, and PCR.
Differential Diagnosis
Key distinguishing features include:
Visual acuity is typically preserved in conjunctivitis and subconjunctival hemorrhage but reduced in uveitis, keratitis, and acute angle closure. Discharge is common in conjunctivitis and keratitis but absent in subconjunctival hemorrhage, uveitis, and acute angle closure. Pain is absent in conjunctivitis and subconjunctival hemorrhage but present in uveitis, keratitis, and acute angle closure. Photophobia is typical of uveitis and sometimes keratitis. Pruritus suggests allergic conjunctivitis.
Treatment
Medications
Viral conjunctivitis is managed supportively with artificial tears and cold compresses; topical steroids are rarely required. Mild bacterial conjunctivitis is treated with topical antibiotics such as trimethoprim-polymyxin B or a fluoroquinolone for several days. Bacterial keratitis requires intensive fortified topical antibiotics administered hourly. Acute bacterial endophthalmitis is treated with intravitreal antibiotics targeting gram-positive and gram-negative organisms. Anterior uveitis is treated with topical corticosteroids and cycloplegic agents; infectious causes require specific antimicrobial therapy. Acute angle-closure glaucoma requires urgent reduction of intraocular pressure with systemic acetazolamide, intravenous mannitol, topical beta-blockers, and pilocarpine, followed by laser iridotomy. Episcleritis is treated with artificial tears, topical steroids, and oral NSAIDs. Scleritis often requires systemic corticosteroids and may necessitate immunomodulatory therapy depending on associated systemic disease.
Additional Treatment / Surgery
Laser iridotomy is definitive for angle closure after stabilization. Severe infectious keratitis or scleritis causing tissue thinning may require surgical grafting.
Prognosis
Outcome depends on etiology, ranging from benign in subconjunctival hemorrhage to guarded in endophthalmitis.
Complications
Chronic inflammation may lead to cataract formation, secondary glaucoma, and cystoid macular edema.
Basics
Description
Red eye may result from sight-threatening conditions such as uveitis, endophthalmitis, acute angle-closure glaucoma, or scleritis, which typically produce ciliary injection. More commonly, redness is due to conjunctival hyperemia associated with conjunctivitis, keratitis, dry eye disease, foreign body irritation (including contact lenses), blepharitis, or environmental irritants. Ocular trauma may cause subconjunctival hemorrhage. Not all causes are infectious. Uveitis involves intraocular inflammation and may be anterior, posterior, or pan-uveitis. Endophthalmitis is a severe intraocular infection involving the vitreous cavity. Acute angle-closure glaucoma is an ophthalmic emergency caused by obstruction of aqueous outflow and elevated intraocular pressure. Episcleritis affects superficial scleral tissues, while scleritis is a deeper, more severe inflammatory process that may occur with keratitis or uveitis. Conjunctivitis is the most common cause of red eye and usually includes discharge. Keratitis primarily affects the cornea.
Epidemiology
Primary acute angle closure occurs more frequently in Asian populations than in Caucasians. Incidence rates for conjunctivitis, keratitis, and uveitis vary and are addressed in their respective discussions.
Risk Factors
Risk factors for angle-closure glaucoma include advanced age, hyperopia, cataract, female sex, prior angle closure in the fellow eye, and Asian ethnicity; prophylactic laser iridotomy is often performed in the unaffected eye. Contact lens use increases the risk of bacterial keratitis. Subconjunctival hemorrhage may occur spontaneously or with bleeding disorders, minor trauma, or increased venous pressure from coughing or sneezing. Autoimmune connective tissue disorders are associated with ocular inflammation, and uveitis may be an initial manifestation.
General Prevention
Proper contact lens hygiene reduces infectious and inflammatory complications. Screening with gonioscopy and preventive laser iridotomy can prevent acute angle closure in high-risk individuals.
Pathophysiology
Ciliary injection involves deeper vascular branches and indicates inflammation of the cornea, iris, ciliary body, or sclera. Conjunctival injection is superficial, mobile with the conjunctiva, and improves with topical vasoconstrictors. Acute angle closure usually results from pupillary block, causing pressure differential between the posterior and anterior chambers, forward bowing of the iris, and obstruction of aqueous outflow through the trabecular meshwork.
Etiology
Conjunctivitis, keratitis, uveitis, and endophthalmitis have infectious and noninfectious causes. Acute angle-closure glaucoma and subconjunctival hemorrhage are noninfectious. Episcleritis is usually idiopathic, though immunologic reactions to herpes simplex or varicella zoster may occur. Scleritis is rarely infectious but may result from systemic infections or extension from keratitis; reported pathogens include fungi (Aspergillus, Fusarium), herpes viruses, mycobacteria, Nocardia, Pseudomonas, Proteus (after scleral buckle procedures), syphilis, leprosy, Lyme disease, and tuberculosis.
Commonly Associated Conditions
Endophthalmitis most commonly follows intraocular surgery. Contact lens wear strongly predisposes to bacterial keratitis.
Diagnosis
History
Subconjunctival hemorrhage is unilateral, painless, and vision is unaffected. Conjunctivitis often begins in one eye but is commonly bilateral and features discharge with minimal visual change. Keratitis is usually unilateral and associated with redness, foreign body sensation, tearing, and decreased vision. Uveitis presents with reduced vision, photophobia, and ocular pain. Acute angle-closure glaucoma presents with severe unilateral pain, decreased vision, nausea, and vomiting. Anterior scleritis causes severe pain and tenderness; posterior scleritis may cause significant visual impairment with less obvious redness. Episcleritis resembles conjunctivitis but has mild discomfort and no discharge. Endophthalmitis presents with pain and significant vision loss.
Physical Examination
Slit-lamp examination is essential. Subconjunctival hemorrhage appears as a sharply demarcated red patch under the conjunctiva. Conjunctivitis shows hyperemia, discharge, membranes or pseudomembranes, papillary or follicular reaction, and possibly preauricular lymphadenopathy. Keratitis reveals epithelial defects, stromal opacities, discharge, and anterior chamber inflammation. Anterior uveitis is diagnosed by inflammatory cells in the anterior chamber and keratic precipitates. Acute angle closure presents with a mid-dilated poorly reactive pupil, corneal edema, and elevated intraocular pressure.
Diagnostic Tests and Interpretation
Laboratory Studies
Routine cultures are unnecessary in typical conjunctivitis except in hyperacute cases suggestive of Neisseria gonorrhoeae. Keratitis lesions are sampled for Gram stain and culture.
Imaging
Confocal microscopy assists in diagnosing Acanthamoeba keratitis. Neuroimaging may identify vascular abnormalities such as carotid-cavernous fistulas or arteriovenous malformations associated with red eye.
Diagnostic Procedures/Other
Corneal biopsy may be needed for refractory keratitis. Vitreous sampling during vitrectomy can assist in diagnosing uveitis or endophthalmitis via cytology, culture, and PCR.
Differential Diagnosis
Key distinguishing features include:
Visual acuity is typically preserved in conjunctivitis and subconjunctival hemorrhage but reduced in uveitis, keratitis, and acute angle closure. Discharge is common in conjunctivitis and keratitis but absent in subconjunctival hemorrhage, uveitis, and acute angle closure. Pain is absent in conjunctivitis and subconjunctival hemorrhage but present in uveitis, keratitis, and acute angle closure. Photophobia is typical of uveitis and sometimes keratitis. Pruritus suggests allergic conjunctivitis.
Treatment
Medications
Viral conjunctivitis is managed supportively with artificial tears and cold compresses; topical steroids are rarely required. Mild bacterial conjunctivitis is treated with topical antibiotics such as trimethoprim-polymyxin B or a fluoroquinolone for several days. Bacterial keratitis requires intensive fortified topical antibiotics administered hourly. Acute bacterial endophthalmitis is treated with intravitreal antibiotics targeting gram-positive and gram-negative organisms. Anterior uveitis is treated with topical corticosteroids and cycloplegic agents; infectious causes require specific antimicrobial therapy. Acute angle-closure glaucoma requires urgent reduction of intraocular pressure with systemic acetazolamide, intravenous mannitol, topical beta-blockers, and pilocarpine, followed by laser iridotomy. Episcleritis is treated with artificial tears, topical steroids, and oral NSAIDs. Scleritis often requires systemic corticosteroids and may necessitate immunomodulatory therapy depending on associated systemic disease.
Additional Treatment / Surgery
Laser iridotomy is definitive for angle closure after stabilization. Severe infectious keratitis or scleritis causing tissue thinning may require surgical grafting.
Prognosis
Outcome depends on etiology, ranging from benign in subconjunctival hemorrhage to guarded in endophthalmitis.
Complications
Chronic inflammation may lead to cataract formation, secondary glaucoma, and cystoid macular edema.
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