by Shady Awwad, MD

Epidemiology:
World leading cause of preventable blindness
Definition:
Infection caused by serotypes A,B,Ba, and C of Chlamydia trachomatis
It is the disease of the under-priviledged populations with poor condition and hygiene.
The main vector is the common fly
Presentation:
Usually bilateral
During childhood:
Bulbar and conjunctival follicles and diffuse inflammation with papillae
Chronic inflammation leading to conjunctival scarring
+/- Trichiasis with corneal complications like scarring in older children and adults.

WHO classification: TF: Trachomatous follicular reaction of more than 5 follicles larger than 0.5 mm on the upper tarsus TI: associated thickening due to infiltration and papillary hypertrophy obscuring 50% of the large deep tarsal vessels TS: conjunctival scarring( feathered bands seen on the upper palpebral conjunctiva) TT: Trichiasis or entropion CO: corneal opacification( causing a visual acuity of <20/60)

Clinical findings:
Course:
Initially a chronic follicular conjunctivitis of childhood that progresses to conjunctival scarring.
In-turned eyelashes might occur in adulthood due to conjunctival scarring and the resultant contraction and decrease in surface area of the conjunctiva. The constant rubbing and resultant abrasions of the cornea by the in-turned eyelashes lead to corneal scarring in late adulthood.
In infants and children, the infection is usually insiduous.
In adults, it is usually acute or subacute.

The signs and symptoms of infection are usually :
Tearing, pain, photophobia,exudation, edema of the eyelids, chemosis of the bulbar conjunctiva, hyperemia, papillary hypertrophy, tarsal and limbal follicles, superior keratitis, pannus formation, and a small, tender preauricular node.
The pathognomonic cicatricial remains of the follicles are known as Herbert's pits: they are small excavations or depressions in the conjunctival tissue at the limbocorneal junction.
The pannus is a fibrovascular membrane that originates from the limbus toward the cornea.
The signs of trachoma are usually more severe and more frequently present in the superior half of the cornea rather than the lower.

Fig. 1: Herbert's pits

Fig. 1 annotated
Diagnosis:
Two out of five criteria need to be fulfilled in order to establish the diagnosis:
1. Follicles(five or more on the flat tarsal conjunctiva)
2. Typical conjunctival scarring at he upper tarsal conjunctiva
3. Limbal follicles or Herbert's pits
4. Fibrovascular Pannus, mostly at the upper limbus 
Laboratory findings:
Chlamydia inclusions can be found in Giemsa-stained conjunctival scrapings, but they might not be always present. The inclusions look like dark purple or blue cytoplasmic masses capping the nucleus of the epithelial cell.
Fluorescein antibody stains and enzyme immunoasssay tests are also available commercially and are more sensitive than Giemsa stains.
Complications:
Scarring of the conjunctiva can destroy the ductules of the accessory lacrimal glands and obliterate the orifices the lacrimal gland, decreasing the aqueous component of the tear film.
The pre-corneal tear film might lose its mucinous component by loss of goblet cells in the conjunctiva from scarring.
The scars may distort the upper lid with subsequent inward deviation of the eyelashes(trichiasis) or the lid margin (entropion): the eyelashes might then abrade the cornea resulting in ulcers and scarring.
Treatment:
Is only given for the active infections, not for the adult who is suffering from the late complications of trachoma.
Tetracycline 1-1.5 g/d PO divided into four doses for 3-4 weeks
Doxyxycline 100 mg PO BID for 3 weeks
Erythromycin 1 g/d PO in 4 divided doses for 3-4 weeks.
Topical ointments or drops used QID for 6 weeks are equally effective
The maximum effect of the therapy is however not achieved before 10-12 weeks. This should not be misinterpreted as failure to respond to the given treatment.

Fig. 2: Concretions: these are calcified bodies that are present in the sub-conjunctival space in the upper palpebral area. They are the product of chronic inflammation. They may be the cause of foreign body sensation in chronic trachoma patients.

Fig. 2: annotated