This is a conjunctival vasodilatation of the vessel. It is caused by the release of histamine, often due to irritation of the conjunctiva. Vasodilation then causes swelling of conjunctiva.
The symptoms include eye redness, which is a complication associated with application of contact lenses. Hyperemia is not only caused by mechanical trauma from a contact lens, but also by the action of chemical solutions, by allergic reaction to these chemicals, or by sediment, or infection.