Trachoma is the most common infectious cause of blindness in the world and is due to recurrent ocular surface infection and secondary scarring from Chlamydia trachomatis. Repeat infection with this organism leads to conjunctival inflammation and scarring, trichiasis, and ultimately blinding corneal opacification.
The World Health Organization (WHO) reports trachoma is endemic to more than 50 countries, with most blinding trachoma in Africa with cases still being reported in the Middle East and North west India and parts of Southeast Asia as well the b. An estimated 21 million people are living with active trachoma and another 2.2 million people are blind or severely visually impaired. Furthermore, 7.3 million people suffer from trichiasis and are at risk for developing blindness.
Epidemiologic studies have shown active trachoma is most common in young children with the prevalence of active trachoma decreasing with age. The long-term sequelae of trachoma infection, including scarring, trichiasis and corneal opacification in adults relates to their exposure to active trachoma when they were young. The gender distrubtion of active trachoma is similar; however, scarring and trichiasis are more common in women than men because women are more likely to care for young children and have longer exposure to the disease.
Trachoma is caused by the bacterium Chlamydia trachoma's four ocular serotypes of Chalmydia trachomatis: A, B, Ba and C. Infection with genital serotypes D to K can cause isolated episodes of ophthalmia neonatorum in infants or inclusion conjunctivitis in adults and do not generally lead to blindness.
Blindness from trachoma is due to recurrent episodes of active infection over months to years. The initial infection is confined to the conjunctival epithelium and triggers an immune response. Repeat infections with subsequent inflammatory responses results in tissue destruction, corneal vascularisation, scarring, cicatricial entropion with trichiasis, and finally corneal opacification from unturned lashes rubbing against the cornea.
Risk factors for trachoma include things that favor transmission of the organism. Examples include:
- Inadequate Water Supply: less water availabe to use for facial cleansing
- Poor Facial Hygiene: secretions around the eye attracts flies that are physical vectors for C. trachomatis tranmission
- Latrine Access: limited latrine access leads to increased fecal contamination of the environment which provides a breeding environment for the fly.
- Overcrowded Living Conditiosn: close contact, especially between children sleeping in same bed, enables exchange of secretion.
- Geographical distribution: parts of North Africa, Middle East, North west India and parts of Southeast Asia.
The WHO grading system: 
|Trachomatous Inflammation (TF)||The presence of 5 or more follicles (>0.5 mm) in the upper tarsal conjunctiva|
|Trachomatous Inflammation (TI)||Inflammatory thickening of the tarsal conjunctiva that obscures more than half of the deep normal vessels|
|Trachomatous Scarring (TS)||The presence of scarring in the tarsal conjunctiva|
|Trachomatous Trichiasis (TT)||At least one lash rubs on the eyeball|
|Corneal Opacity||Easily visible corneal opacity over the pupil|
The clinical manifestations of trachoma can be divided into findings associated with active disease and those associated with repeat infections.
- Follicular Conjunctivitis: Follicles are dome-shaped collections of lympoid cells. The center of the follicle is avascular and has blood vessels that surround the round base. These appear as yellow-white elevations and are prominent on the everted upper eyelid in trachoma. Large conjunctival follicles located at the upper margin of the cornea may leave depressions known as 'Herbert's pits' which are pathognomonic for trachoma.
- Papillary Hypertrophy: engorgement of small vessels with edema that can obscure deep tarsal vessels
- Corneal Pannus: vascularization of the upper cornea.
Repeat Infection and Inflammation:
- Conjunctival Scarring: White bands or lines that represent fibrosis
- Cicatricial Entropion and Trichiasis: Fibrotic scar tissue contraction causes the eyelid turning inward and lashes touching the eyeball.
- Corneal Opacification: secondary to repeat corneal irritation from inward turning eyelashes
Trachoma is a clinical diagnosis based on the above mentioned clinical findings. PCR testing developed for urogenital infection is available but typically utilized for research purposes only. Some of the available diagnostic tools include: cytologic tests (Giemsa stain or direct fluorescent antibodies), different cell cultures and enzyme immunoassay methods. These three methods have been surpassed in both sensitivity and specificity by nucleic acid amplification tests (NAATs). Currently, there is insufficient evidence to support the use of NAATs for national elimination programs
Histopathological studies of active inflammatory trachoma are characterized by diffuse mixed inflammatory cell infiltrate of the conjunctiva, mild to moderate epithelial hyperplasia and lymphoid follicles in the stroma; the latter being a clinical and pathological hallmark of trachoma. In cicatricial trachoma, the conjunctiva may display a chronic inflammatory infiltrate, mostly marked in the substantia propria with predominantly lymphocytes. Conjunctival epithelium may show squamous metaplasia or atrophy with multiple denuded areas. Underneath this epithelium, stroma may be replaced with thick, compact avascular scar tissue.  
Most individuals are asymptomatic or have mild symptoms depending on the level of inflammation. Symptoms, if present, are similar to those seen in any chronic conjunctivitis and include redness, discomfort, tearing, photophobia and muco-purulent discharge.
The World Health Organization recommends the 'SAFE' strategy for the management of trachoma. This strategy was developed in 1997 by The Alliance for the Global Elimination of Blinding Trachoma by the year 2020 (GET 2020) and utilizes a 4 step approach:
- S: Surgery for Trichiasis
- A: Antibiotics for C. trachomatis infection
- F: Facial cleanliness
- E: Environmental change to improve sanitation and increase access to clean water.
Prevention is ideally the best strategy which includes hygiene, public education coupled with increased awareness.
Early management should be medical with appropriate and early use of antibiotics with completion of treatment of patient and his/her contacts.
Surgical management is reserved for late and advanced cases after maximum medical ocular surface management. This may include simple measures to redirect eyelashes and eyelid margin away from the cornea to more invasive procedures like posterior lamellar augmentation(grafts), eyelid eversion.
- Boyd K, Pagan-Duran B. Trachoma. American Academy of Ophthalmology. EyeSmart® Eye health. https://www.aao.org/eye-health/diseases/trachoma-list. Accessed March 25, 2019.
- Boyd K. Trichiasis. American Academy of Ophthalmology. EyeSmart® Eye health. https://www.aao.org/eye-health/diseases/trichiasis-list. Accessed March 25, 2019.
- WHO/Department of control of neglected tropical diseases. Trachoma simplified grading card SAFE documents. World Health Organization (WHO), 1987. http://www.who.int/trachoma/resources/SAFE_documents/en/ Accessed 10 October 2017
- Hu VH, Holland MJ, Burton MJ. Trachoma: protective and pathogenic ocular immune responses to Chlamydia trachomatis. PLoS neglected tropical diseases. 2013; 7(2), e2020.
- Keenan JD, Lietman TM. Chlamydial infections. In Cornea. 4th ed. Elsevier Mosby. 2016; 503–507.