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OP4.6 | Corneal Blindness — SDL Guide (Part 2)

Trachoma as a Cause of Corneal Blindness

Trachoma is caused by Chlamydia trachomatis serotypes A, B, and C (the ocular trachoma strains — distinct from the urogenital strains D-K that cause sexually transmitted infection). It is the world's leading infectious cause of preventable blindness, responsible for approximately 1.9 million cases of visual impairment globally, concentrated in communities with poor sanitation and limited access to clean water. The organism is transmitted by eye-seeking flies (Musca sorbens), direct contact with infected eye secretions, and fomites such as shared towels. What makes trachoma clinically distinctive — and epidemiologically insidious — is its mechanism of blinding: trachoma does not destroy the cornea directly during the acute infectious phase. Instead, repeated episodes of conjunctival infection in childhood trigger a chronic inflammatory response that gradually scars the upper tarsal conjunctiva. Over years and decades, this scarring contracts the upper eyelid, eventually causing inward rotation of the lid margin (entropion) and misdirection of the eyelashes toward the globe (trichiasis). The trichiatic lashes then abrade the corneal epithelium with every blink — thousands of times per day — producing repeated epithelial trauma, secondary bacterial infection, corneal vascularisation, and ultimately dense central leukoma. This long latency between childhood infection and adult blindness means that the person going blind in middle age acquired their infection thirty years earlier — making trachoma a disease that requires population-level, multi-decade prevention strategies, not just individual treatment.

The WHO simplified trachoma grading (for field use) classifies the disease in five stages:
- TF (Trachomatous Follicles): ≥5 follicles (≥0.5 mm diameter) in the upper tarsal conjunctiva; active, infectious stage in children
- TI (Trachomatous Intense Inflammation): Pronounced inflammatory thickening of the upper tarsal conjunctiva obscuring >50% of the normal blood vessels; highly infectious
- TS (Trachomatous Conjunctival Scarring): Scarring of the upper tarsal conjunctiva — white streaks, bands, or sheets; cicatricial stage
- TT (Trachomatous Trichiasis): At least one eyelash rubs against the globe, or evidence of recent epilation (misdirected eyelashes from cicatricial lid entropion scratch the cornea)
- CO (Corneal Opacity): Corneal opacity over the pupil; causes significant visual impairment; the end-stage blinding complication

The mechanism of blindness: repeated childhood infections (TF, TI) cause conjunctival scarring (TS). The upper lid scarring shortens and contracts, causing entropion (inward turning of the lid margin). The misdirected eyelashes (trichiasis) rub against the cornea with every blink — causing repeated epithelial trauma, secondary bacterial infection, and ultimately corneal vascularisation and leukoma formation (CO).

The WHO SAFE strategy for trachoma elimination:
- S — Surgery: Bilamellar tarsal rotation for trichiasis (corrects entropion surgically — removes the mechanical cause of corneal abrasion)
- A — Antibiotics: Single oral dose azithromycin 1 g (adults) or 20 mg/kg (children) eliminates active Chlamydia infection; mass drug administration (MDA) in endemic communities
- F — Facial cleanliness: Washing the face (especially around the eyes) reduces fly landing and transmission
- E — Environmental improvement: Improved sanitation, water access, and fly control at community level

India has significantly reduced trachoma prevalence through NPCBVI-linked trachoma control programmes; it is no longer hyperendemic in most of India, but pockets persist.

Prevention and Control of Corneal Blindness in India

India's primary instrument for blindness control is the National Programme for Control of Blindness and Visual Impairment (NPCBVI), launched in 1976 and periodically revised. It is a Centrally Sponsored Scheme operating through District Blindness Control Societies (DBCS) at the district level. The programme targets cataract, corneal blindness, glaucoma, childhood blindness (including vitamin A deficiency), and diabetic retinopathy.

Vision 2020: The Right to Sight is a joint initiative of WHO and the International Agency for the Prevention of Blindness (IAPB), launched in 1999 and subsequently extended beyond 2020. Its goal is the elimination of avoidable blindness by addressing preventable causes (trachoma, onchocerciasis, vitamin A deficiency) and ensuring treatment for treatable causes (cataract, refractive error, childhood blindness, glaucoma, diabetic retinopathy). India is a signatory and has adopted Vision 2020 goals into NPCBVI targets.

Primary prevention strategies for corneal blindness include:
- Vitamin A supplementation programme: bi-annual supplementation of all children 6 months to 5 years under ICDS/Anganwadi network
- Trachoma control: SAFE strategy; MDA with azithromycin in endemic districts
- Occupational eye protection: enforcement of eye protection standards in agriculture and industry
- Early treatment of corneal ulcers: primary health centre training to identify and refer corneal ulcers urgently, rather than treating with empirical antibiotics + steroids
- School eye health: screening for refractive error and early corneal anomalies in children

Eye donation and eye banking are central to treatment: keratoplasty requires donor corneal tissue from deceased donors. India has approximately 750+ registered eye banks, but cornea procurement remains far below the surgical demand. Voluntary eye donation is promoted through the National Eye Donation Fortnight (August 25–September 8 annually) and through hospital-based counselling of relatives of recently deceased patients.

Rehabilitation and Treatment of Established Corneal Blindness

When corneal blindness is established — typically a dense bilateral central leukoma from post-infective or post-keratomalacia scarring — the treatment options for visual rehabilitation depend on the condition of the entire eye.

Keratoplasty (penetrating or deep anterior lamellar, as described in SDL 4) is the definitive surgical treatment. In India, the limiting factor is corneal tissue supply: the eye banking network procures significantly fewer corneas than the surgical demand (~150,000–200,000 grafts needed per year vs ~30,000–40,000 performed). The causes of this gap include: low voluntary eye donation rates, inadequate hospital infrastructure for consent and retrieval, and geographic concentration of eye banks in urban centres.

Low vision aids: For patients with partial vision or those awaiting keratoplasty, magnification devices (hand-held magnifiers, stand magnifiers, telescopes for distance), contrast-enhancing filters, and screen readers enable some functional activity. Low vision clinics in district hospitals are part of the NPCBVI infrastructure.

Counselling and social rehabilitation: Corneal blindness in a working-age adult or breadwinner has devastating socioeconomic consequences. Integration of social welfare benefits, Braille education (for total blind), vocational retraining, and ophthalmology social worker support are important components of care that extend beyond the clinic.

For chemical burns causing corneal opacity — lime (calcium hydroxide) and ammonia are the commonest alkali causes in India — the acute management involves copious irrigation (the most important first step, ideally begun within seconds of the injury), pH testing, and specialist referral. Chronic management of the chemical-burn cornea includes managing limbal stem cell deficiency (the limbal stem cells are destroyed by alkali burns), with limbal stem cell transplantation or keratolimbal allograft before or concurrent with keratoplasty.

Self-Assessment: Corneal Blindness

Apply your understanding to these questions.

Question 1: A 2-year-old child in a rural area is brought in with night blindness, Bitot's spots, and now corneal haziness beginning in both eyes. Name the WHO xerophthalmia stage (giving the code), state whether this is an emergency, and write the vitamin A dose you would give. Answer: Stage X2 (corneal xerosis). YES — this is approaching keratomalacia territory and is an emergency once corneal involvement begins. Vitamin A: 200,000 IU orally today (day 1), repeated tomorrow (day 2), and again in 2 weeks (day 14). Start immediately without waiting for any investigation.

Question 2: Name the four components of the WHO SAFE strategy for trachoma, and state the drug used in the 'A' (Antibiotic) component. Answer: Surgery (bilamellar tarsal rotation for trichiasis), Antibiotics (azithromycin — single oral dose, MDA), Facial cleanliness, Environmental improvement. The antibiotic is azithromycin.

Question 3: A 35-year-old man in Kerala lost his left eye's vision 5 years ago from a fungal keratitis that left a central leukoma. His right eye is normal (6/6). Is he 'blind' by WHO definition? Does he qualify for NPCBVI programme benefits? Answer: Not bilaterally blind (WHO blindness requires VA <3/60 in the BETTER eye — his better eye is 6/6). Monocularly blind. Under NPCBVI, bilateral blindness is the eligibility criterion for most surgical rehabilitation support, so he does not qualify for the corneal surgery support programme. This highlights an important equity gap — monocular blindness significantly affects occupational functioning but is underserved by national programmes.