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^†
  
  • 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 Eye
Examination of the Ocular Fundus. Part 1. Normal Appearance & Light Responses
Examination 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.