Diagnosing trachoma

In public health, there are three essential questions: What is the condition? Who in the population has it? What effective intervention do we have?

Using this information, a health programme can be planned and implemented.

In order to identify what a condition is, we need a clear and agreed definition that is simple enough for trained health personnel to use.

Grading trachoma

Throughout the long history of trachoma, clinicians have tried to describe and define the disease as seen in individuals. Early attempts to define the disease stages were mainly based on observations made on the clinical severity of disease – suspicion, mild, moderate, severe.

However, this subjective definition was problematic when used to describe trachoma in a population and to establish health programmes. In 1913, the MacCallan classification of trachoma with 4 ‘simple’ disease stages was published. It was widely accepted and used as a standard for over 60 years. It was also adopted and further adapted by the first WHO expert committee in 1952.

In 1966, the fourth WHO expert committee introduced a new trachoma grading scheme. This was based on up to 22 clinical signs and, although useful for researchers, it was too complicated to be used in health programmes. Further refinements and modifications focused on identifying five fundamental signs of trachoma and in 1987, the WHO published a simplified grading system that is used to assess communities for trachoma and monitor the impact of trachoma elimination activities.

This simplified grading scheme was used by teams during the Global Trachoma Mapping Project, and is now used by teams undertaking surveys supported by Tropical Data. It is also used in many countries by a wide range of trained health personnel at the hospital and community level.

WHO simplified trachoma grading system

• TF = Trachomatous inflammation—follicular: the presence of five or more follicles, each at least 0.5mm in diameter, in the central part of the upper tarsal conjunctiva.
• TI = Trachomatous inflammation—intense: pronounced inflammatory thickening of the upper tarsal conjunctiva that obscures more than half of the normal deep tarsal vessels.
• TS = Trachomatous scarring: scarring of the tarsal conjunctiva (fibrosis).
• TT = Trachomatous trichiasis: at least one eyelash from the upper eyelid rubbing on the eyeball or evidence of recent removal of in-turned eyelashes from the upper eyelid.
• CO = Corneal opacity: corneal scarring so dense that at least part of the pupil margin is blurred when viewed through the opacity.

As you watch this video, consider why it is that the TF and TT grades are used at a programme level and not all five signs?