Trachoma and its WHO grading

What it is

Trachoma is caused by C. trachomatis and is the leading infectious cause of blindness in the world.

The same organism gives chlamydial conjunctivitis, which affects neonates as ophthalmia neonatorum on day 3-5 and sexually active individuals, and it causes both trachoma and inclusion conjunctivitis. One cause, three faces, and trachoma is the one that ends in blindness.

How it presents

Initially there are follicles on the superior palpebral conjunctiva. Severe keratoconjunctivitis leads to corneal abrasion, ulceration and scarring, and that chain is what ends in blindness.

The stages, read on the everted upper eyelid

For examination the upper eyelid is everted. The stage is then read on the tarsal conjunctiva, and each stage is fixed by what is seen there.

• N, normal tarsal conjunctiva: notice the large deep-lying blood vessels that mainly run vertically. This is what the next two stages are read against
• TF, trachomatous inflammation follicular: presence of 5 or more follicles in the upper tarsal conjunctiva, each at least 0.5 mm in size
• TI, trachomatous inflammation intense: pronounced inflammatory thickening of the upper tarsal conjunctiva, which obscures more than one half of the normal tarsal vessels
• TS, trachomatous scarring: the presence of easily visible white lines, bands, or sheets in the tarsal conjunctiva; the scarring may obscure the tarsal vessels
• TT, trachomatous trichiasis: at least 1 eyelash that rubs the globe, or evidence of recently removed lash, that is epilation
• CO, corneal opacity: the presence of an easily visible corneal opacity that obscures at least part of the pupillary margin

Of the six, four of the six turn on a count or on how much is obscured: TF asks how many follicles and how large; TI asks how much of the normal tarsal vessels is obscured; TS asks whether the scarring obscures them; and CO asks how much of the pupillary margin the opacity obscures.