The corneal is a layer of transparent film on the front of the eyeball. It often exposed in the air, so it would get more chance of virus infection than other issues of eyes.
As reasons for the corneal ulcer, when the trauma or corneal hurt as well as trachoma complication symptom happens, the virus and bacterials get into the inner of corneal, the corneal ulcer will be reduced. As for the signs of corneal ulcer, the rete vasculosum will get expanded and congestion on the edge of corneal, it named ciliary congestion. The infiltration of corneal will happen at the same time by the invasion of white blood cell. When the infiltration get heavy, the issues of corneal get degeneration, necrosis, or drop, it will become corneal ulcer.
The corneal abrasion just a normal trauma that caused by outer factor of clashing. It is not caused by the reason of virus and bacterials. The most differences between the two disease is if it will infiltration, the corneal ulcer will cause corneal get degeneration, necrosis, or drop. They are different!