chemosis

This is swelling of the conjunctiva skin, usually from allergy.  The surface of the eye is covered by a very thin layer of skin called the conjunctiva. This skin layer is clear, but has blood vessels running through it that you can see when looking at the white of the eye in the mirror.  Irritation to this skin causes fluid to collect under the surface and bulge this skin forward.  This swelling can be quite impressive and alarming.  As long as the vision is unchanged, however, this is rarely an emergency.  Treatment usually involves allergy drops and occasionally steroid eye drops to decrease swelling.