Red Eye
Is it conjunctivitis or something more serious? Use this diagnostic tree to find out what's causing that red eye.
Checklist: Examining the Red Eye
Observe eye to determine what part(s) are affected, what appears normal/abnormal, whether eye is painful, and presence of discharge.
Develop list of diagnostic differentials based on ocular changes and conduct diagnostic testing.
Determine whether eye is visual.
Assess pupil size and light reflexes.
Perform STT for quantitative assessment of tear production.
Perform ocular surface staining:
Fluorescein staining to assess corneal epithelium defects, NLD patency, and tear film breakup time and stability
Seidel’s test to identify leakage of aqueous humor through cornea
Rose bengal staining to measure precorneal tear film quality and integrity
Perform tonometry to estimate IOP: elevation consistent with glaucoma, decrease consistent with intraocular inflammation.
Complete examination and systemic diagnostic testing as indicated.
Blepharospasm present?
Yes
Diagnostic Differentials
Corneal ulcer
Anterior uveitis
Acute glaucoma
Acute lens luxation
No
Diagnostic Differentials
Chronic keratitis
Chronic glaucoma
Posterior segment hemorrhage/disease (in absence of anterior uveitis)
Episcleritis
Pupil size?
Miotic
Diagnostic Differentials
Anterior uveitis (alone or as reflex reaction to corneal ulcer)
Mid-range
Diagnostic Differentials
KCS/conjunctivitis
Keratitis
Corneal ulcer without accompanying anterior uveitis
Episcleritis
Anterior uveitis with secondary glaucoma
Acute congestive glaucoma
Mydriatic
Diagnostic Differentials
Subacute or chronic glaucoma
Posterior segment disease (retina, optic nerve)
Iris atrophy
Discharge present?
Yes
Serous
Diagnostic Differentials
Acute conjunctivitis
Corneal ulcer
Anterior uveitis
Acute glaucoma
Mucoid
Diagnostic Differentials
KCS
Chronic conjunctivitis
Chronic keratitis
No
Diagnostic Differentials
Chronic glaucoma
Posterior segment hemorrhage/disease (in absence of anterior uveitis)
Conjunctival Congestion or Episcleral Injection?
Conjunctival vessels are movable over sclera
Episcleral vessels are fixed and typically larger
Conjunctival vessels will blanch more rapidly following application of a vasoconstricting agent (ie, phenylephrine, epinephrine)
What part of the eye is red?
Anterior chamber
Diagnostic Differentials:
Hyphema
Interior uveitis
Trauma
Retinal detachment
Systemic hypertension
Intraocular neoplasia (primary or metastatic)
Bleeding disorder
Investigation
Ultrasonography
Systemic workup*
Fluorescein staining
Pupil size
IOP
Fundus (reflection)
Diagnostic Differentials:
Variation of normal (atapetal or hypo-pigmented)
Posterior segment hemorrhage
Retinal detachment
Chorioretinitis
Systemic hypertension
Bleeding disorder
Intraocular neoplasia (primary or metastatic)
Investigation
Ultrasonography
Systemic workup*
Fluorescein staining
Pupil size
IOP
Iris
Diagnostic Differentials
Anterior uveitis (iridal hyperemia or intrastromal homorrhage)
Intraocular neoplasia (primary or metastatic)
Bleeding disorder
Investigation
Ultrasonography
Systemic workup*
Fluorescein staining
Pupil size
IOP
Cornea<sup†sup>
Diagnostic Differentials
Uveitis
Glaucoma
KCS (quantitative & qualitative)
Keratitis
Corneal ulcer
Investigation
STT
Rose bengal staining
Cytology
Fluorescein staining
Conjunctiva
Diagnostic Differentials
Conjunctivitis (allergic, bacterial, viral)
KCS (quantitative & qualitative)
Excitement
Investigation
STT
Rose bengal staining
Cytology
Fluorescein staining
Sclera/episclera
Diagnostic Differentials
Glaucoma
Anterior uveitis
Lens luxation
Corneal ulcer
Episcleritis
Excitement (scleral injection)
Scleral hemorrhage (trauma)
Investigation
Fluorescein staining
Pupil size
IOP
IOP = intraocular pressure, KCS = keratoconjunctivitis sicca, NLD = nasolacrimal duct, STT = Schirmer’s tear test
* Systemic workup = minimum database, systemic blood pressure, coagulation parameters, infectious disease titers, thoracic/abdominal imaging† The cornea itself is rarely red unless vascularization is present; blood may also be present within the stroma or behind the cornea, within the anterior chamber, giving the impression of a red cornea
Related Articles:The Red EyeExamination of the Ocular Fundus. Part 1. Normal Appearance & Light ResponsesExamination of the Ocular Fundus. Part 2: Indirect and Direct Ophthalmoscopy
CARYN E. PLUMMER, DVM, Diplomate ACVO, is assistant professor of ophthalmology in the department of clinical sciences at the University of Florida College of Veterinary Medicine. In addition, she is an associate ophthalmologist at Animal Eye Associates of Maitland, Florida, as well as coordinates the ophthalmic surgery laboratories at the annual NAVC Conference. With research interests in corneal disease and glaucoma, Dr. Plummer has also participated in the NAVC Equine Ophthalmology In-Depth Seminar and Laboratories. She is a graduate of University of Florida and completed internship training at Michigan State University, after which she returned to UF for a residency in comparative ophthalmology and received board certification from the American College of Veterinary Ophthalmologists.