Why is prednisone given during an endoscopy?

I had an endoscopy yesterday and my eye was hurting when I woke. I was really groggy so I didn't really think to ask at the time. Now it is the next day and my eye hurts and the lid is all puffed up. I thought I was having an allergic reaction so I called the nurse to ask what I was given during the procedure. She said Versed, Prophynol, Lidocaine, and Prednisone. She said that none of those drugs would do that and she said if it was an allergy both eyes would swell. That doesn't sound right to me. I know the other 3 drugs were necessary but why the Prednisone? Is this usual? Also, I should note the results of the endoscopy were normal.