Which condition may result in a crescent-shaped shadow on the cornea?

A crescent-shaped shadow on the cornea is indicative of an anatomical or functional issue involving the angle of the anterior chamber of the eye. In the case of angle closure, this occurs when the peripheral iris blocks the trabecular meshwork, preventing intraocular fluid from properly draining. As a result, an increased intraocular pressure and altered configuration of the cornea can produce a crescent shadow effect.

This phenomenon is often assessed during a slit-lamp examination, where the specific nature of the shadowing is noted based on the position and orientation of the light source. The presence of a crescent shadow strongly suggests that there is a mechanical obstruction to drainage that is characteristic of angle closure. Understanding this connection helps in diagnosing and managing potential glaucoma, as untreated angle closure can lead to severe complications, including complete vision loss.