Red eye DDx

Overview

Red eye is a catch-all term for the inflamed or injected external appearance of the eye, for which there are many causes.

I like Jeff Mann’s approach to the red eye — he breaks the causes down into 3 groups:

1. extra-ocular causes (e.g. orbital cellulitis, cavernous sinus thrombosis, carotid-cavernous fistula, cluster headache)
2. external eye disease (e.g. eyelid and conjunctival disease)
3. internal eye disease (e.g. iritis, glaucoma)

Once an extra-ocular cause is excluded (this will be discussed in a later post), a helpful approach is to divide up the causes of a red eye as follows:

1. Painless —  is there diffuse or localised redness?
2. Painful?

The next step is to consider which structures are abnormal: Lid, conjunctiva, cornea, sclera, or anterior chamber.

Causes

Painless red eye

These can be classified according to whether the redness is diffuse or localised.

• diffuse
  • usually, this is an eyelid abnormality as most cases of conjunctivitis are painful: e.g. blepharitis, ectropion, trichiasis, entropion, eyelid lesion (e.g. tumour, stye)
• localised
  • e.g. pterygium, corneal foreign body, ocular trauma, subconjunctival hemorrhage

If you’re stuck for a differential diagnosis, fall back on working through the anatomical components of the eye and running through a pathophysiological sieve.

Painful red eye

These can be classified according to which structure is abnormal:

• abnormal cornea
  • e.g. herpes simplex keratitis, corneal ulcer, marginal keratitis, corneal abrasion,
• abnormal eyelid
  • e.g. chalazion/ stye, acute blepharitis, herpes zoster ophthalmicus
• diffuse conjunctival injection
  • e.g. viral conjunctivitis, allergic conjunctivitis, bacterial conjunctivitis, dry eyes, acute glaucoma
• ciliary injection/ scleral involvement
  • e.g. scleritis
• anterior chamber involvement
  • e.g. acute anterior uveitis (iritis), hypopyon, hyphema

References and Links

LITFL

• Ophthalmology Befuddler 002 — The Red Eye Challenge

CCC Differential Diagnosis Series
NEURO	Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision
RESP	Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
CVS	Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction
GIT	Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage
GUT	Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
MSK	Arthritis, Shoulder pain, Wasting of the small muscles of the hand
DERM	Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
ENDO	Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
HAEM	Splenomegaly
PAEDS	Floppy infant
MISC	Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
IMAGING	CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR, ABDO: Gas on abdominal X-ray, Kidney mass, BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly, OTHER: Pseudofracture on X-Ray,
LABS	LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia,  HIGH: Bilirubin and Jaundice, Hyperammonaemia, Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia,  ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis, Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes

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