Causes. There are channels in the eyes that pass fluid to the cornea and iris. If these channels become blocked, pressure on the eye increases, eventually damaging the optic nerve. As this damage progresses, a person begins to lose sight in that eye. It isn’t always known what causes the pressure on the eye, but doctors have identified several possible causes. Eye drops that cause dilation, restriction in the drainage system of the eye, reduced blood flow to the eye, and certain medications, like corticosteroids, are believed to play a role in the development of glaucoma. There are also eye problems that cause swelling and inflammation.