Cicatricial disease: Trichiasis and its sequelae

(A) World Health Organization (WHO) grade TT (trachomatous trichiasis). To make a diagnosis of TT, there must be evidence of at least one eyelash from the upper eyelid touching the eyeball or evidence of recent epilation of in-turned eyelashes from the upper eyelid. Trichiasis occurs when eyelid conjunctiva scar tissue contracts, distorting the lid margin and causing the eyelashes to rub on the cornea.
(B) Pannus. Pannus is the growth of vascular tissue over the cornea as a result of edema and ulceration due to eyelash abrasion on the cornea. It is a hallmark of trachoma but is not assessed in the current grading system.
(C) WHO grade CO (corneal opacity). To make a diagnosis of CO, there must be evidence of corneal opacity blurring part of the pupil margin.