Acute red eye is a common presenting complaint to primary care physicians.  A detailed history of the presenting symptoms and previous ophthalmic and medical history can narrow the differential diagnosis and aid in the interpretation of key examination findings. The lack of specialist equipment in the primary care setting, along with a very broad differential diagnosis, can cause difficulty in establishing the correct diagnosis, and in such cases a specialist ophthalmic opinion should be sought.  Serious vision-threatening conditions that present as red eye are rare and can occasionally be overshadowed by associated systemic symptoms; in light of this they should always be considered within the differential and excluded on examination. 
Sunderland Eye Infirmary
JS declares that he has received travel and meeting costs from Novartis and Bayer.
James Cook University Hospital
PS declares that he has served on the advisory boards of and received travel grants from Bayer and Novartis. He has also received travel grants from Allergan.
Consultant in Ophthalmology
Royal Victoria Infirmary
LC declares that she has no competing interests.
Assistant Professor of Ophthalmology
Cornea External Disease and Refractive Surgery Local Director
Long Island College Hospital Eye Center
MPE declares that he has no competing interests.
Professor of Ophthalmology and Vision Sciences
Centre for Vision Science
Queen's University Belfast
UC declares that she has no competing interests.
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