The "haw" is the name given to a movable membrane covered with conjunctiva, and situated at the inner corner of the eye. Its office is to defend the tender eyeball from injuries threatened from without, and to remove extraneous bodies that may have obtruded within the lids; hence, it is called the "third eyelid."

From external violence, or the irritation induced by foreign bodies, or from some constitutional disorder, the haw becomes congested, inflamed, and enlarged. It then projects at the inner corner of the eye between the lids, and prevents them from closing, and thus causes considerable distress. The same thing takes place when the conjunctiva is inflamed generally, either in the simple, or in the distemper form of ophthalmia.

This disorder should be first treated as partial ophthalmia, with the remedies mentioned under that disease. Should the enlargement continue, it should be excised by transfixing it with a hooked needle, drawing it out, and clipping it off with a pair of sharp scissors.