When a patient comes into the emergency department complaining of red eyes, crusting, and discharge, they are almost always prescribed antibiotic drops. After all, conjunctivitis is so contagious that it can rapidly spread through preschools and day cares within a matter of days. I was always amazed at how fast people would come in to the emergency department to get prescriptions for antibiotics – usually without even bothering to try to get an appointment with their primary care provider.

I didn’t understand why people panicked so much until I woke up one morning with my left eye infected, crusted shut, and extremely puffy. Conjunctivitis! Oh no! I immediately ran to my bathroom cabinet and started using a prescription sulfacetamide drops that I had from last year.

Unfortunately, the next day, I woke up with both of my eyes crusted shut. I was horrified – double pink eye! The drops weren’t working! Did I need a stronger antibiotic? Was I ultimately going to go blind? Should I go to the eye doctor? It wasn’t until I really sat down and thought about my symptoms that I realized I was actually demonstrating the classic signs of viral conjunctivitis. Therefore, no antibiotic was going to help me in this case. I just had to suffer through it and hope that I didn’t infect anyone else.

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When people come into the ED complaining of these symptoms, we quickly write them prescriptions for antibiotic drops. But is this really necessary? The majority of conjunctivitis cases are caused by viruses, primarily adenovirus.1 Therefore, most cases of conjunctivitis don’t need antibiotics.

Getting a good history from a patient can often help differentiate between viral, bacterial, and allergic conjunctivitis. Viral conjunctivitis often has a sudden onset. While it can affect just one eye, it often spreads from one eye to both eyes after a day or two. There will be crusting in the morning, but symptoms usually improve during the day. Discharge is watery in nature, and eyes may feel irritated. There may be some mucoid discharge, but it will be scant. In addition, the biggest clue that it’s viral conjunctivitis is that patients will often report viral symptoms, such as cough, congestion, or pharyngitis. There may be lymphadenopathy as well.  Similar to a viral illness, these symptoms may get worse over the course several days in the beginning but will soon begin to resolve. In addition, it can take a full 2 weeks for symptoms to resolve.1

Unlike viral conjunctivitis, bacterial conjunctivitis is typically unilateral, but it can sometimes spread to both eyes. The biggest indicator of bacterial conjunctivitis is the purulent discharge. It will be very noticeable on exam and is continuous. It will persist throughout the day. When history and physical exams are consistent with this situation, antibiotics will help resolve the infection quickly.

Allergic conjunctivitis is another type of conjunctivitis that cannot go overlooked. I have seen patients in the emergency department with allergic conjunctivitis, and they are absolutely miserable. These patients often have a medical history that includes seasonal allergies. The patient’s exam will reveal extremely pruritic eyes that are continually watering and very infected. There may even be conjunctival swelling. They may even have morning crusting, which can confuse the diagnosis. To differentiate between allergic and viral conjunctivitis, question the patient to see if they have a history of allergies, if they have had any recent exposures to allergens, and to determine the level of pruritus.2 Mast cell stabilizer drops can help patients with allergic conjunctivitis.

It is important to remember that not all red eyes are conjunctivitis. A good history and physical exam are crucial so that things like uveitis and acute angle closure glaucoma are not overlooked. Ever since I had my episode of bilateral conjunctivitis, I have made it a point to try to really counsel patients on the different types of conjunctivitis, explaining to those with viral or allergic types why antibiotic drops are not going to help them. Before my conjunctivitis, I was didn’t understand why so many people came to the ED without even trying to make appointments with an eye doctor or their primary care provider. But despite my medical training, even I was terrified for a brief moment that I was going to go blind. And now? I totally get their point of view. 

Jillian Knowles, MMS, PA-C, works as an emergency medicine physician assistant in the Philadelphia area.


  1. Yeung KK. Bacterial Conjunctivitis. Medscape. https://www.clinicaladvisor.com/home/topics/allergy-and-immunology-information-center/. Updated December 4, 2015. Accessed April 7, 2016.
  2. Jacobs DS. Conjunctivitis. UpToDate. http://www.uptodate.com/contents/conjunctivitis. Updated July 19, 2015. Accessed March 30, 2016.