infiltration of polymorphonuclear and/or lymphocytes into the epithelium
from the peripheral circulation supplemented by similar cells from the underlying stroma if this tissue is also affected. Subsequently necrosis of the
involved tissue may occur, depending upon the virulence of offending agent and the strength of host defense mechanism.
2. Stage of active ulceration (Fig. 1B). Active ulceration results from necrosis and sloughing of the epithelium, Bowman's membrane and the involved stroma. The walls of the active ulcer project owing to swelling of the lamellae by the imbibition of fluid and the packing of masses of leucocytes between them. This zone of infiltration may extend to a considerable distance both around and beneath the ulcer. At this
stage, sides and floor of the ulcer may show grey infiltration and sloughing.
During this stage of active ulceration, there occurs hyperaemia of circumcorneal network of vessels which results into accumulation of purulent exudates on the cornea. There also occurs vascular congestion of the iris and ciliary body and some degree of iritis due to absorption of toxins from the ulcer. Exudation into the anterior chamber from the vessels of iris and ciliary body may lead to formation of hypopyon. Ulceration may further progress by lateral extension resulting in diffuse superficial ulceration or it may progress by deeper penetration of the infection leading to Descemetocele formation and possible corneal perforation. When the offending organism is highly virulent and/or host defence mechanism is
jeopardised there occurs deeper penetration during stage of active ulceration.