This is a sign of many conditions i.e. asthma, infections, heart problems.Patient needs 100% oxygen. Call 911 immediately.
This may cause the common "black eye" but sometimes may involve damage
which is more serious. Always ask the patient if they can see well out of the
injured eye. If not, refer to a physician or to the hospital emergency department.
Also, examine the eye for bleeding behind the clear part of eye (cornea) and
refer to a doctor immediately if blood is seen.
This common injury occurs when welders and those around them expose their eyes
to bright welding flashes. This will cause severe eye discomfort, usually several
hours after the exposure
Taken from the First Aid Pocket Guide