It occasionally happens in an attack or attacks of iritis that the whole pupillary margin of the iris becomes bound down to the lens in the form of a ring or annular synechia. This interrupts the passage of aqueous from the posterior to the anterior chamber. Accumulated hydrostatic pressure behind the iris causes it to bulge forward in the shape of a doughnut or umbrella, a condition designated in ophthalmic parlance as iris bombé or ballooning of the iris. The protrusion is not usually equal all around but is furrowed by depressions where the iris is bound down by adhesions.
The pupil appears as a crater and seems farther depressed because of the bulging of the surrounding iris. The latter may almost fill the anterior chamber, while the forward displacement at the periphery is liable to bring the iris in contact with the cornea, closing the angle of the anterior