A 18-month-old child from rural India presents with poor weight gain, delayed milestone achievement, and recurrent respiratory infections. On examination, there is bitot's spot and corneal haziness. Which vitamin deficiency is the most common cause of blindness in children worldwide?

Explanation

## Vitamin A Deficiency: The Leading Preventable Cause of Childhood Blindness ### Epidemiology & Global Burden **Key Point:** Vitamin A deficiency (VAD) is the leading preventable cause of blindness in children worldwide, particularly in developing countries of South and Southeast Asia and sub-Saharan Africa. **High-Yield:** In India, VAD remains endemic in states with poor nutritional status and limited dietary diversity. The prevalence is highest in children aged 6–59 months. ### Clinical Manifestations in Children | Feature | Timing | Clinical Significance | |---------|--------|----------------------| | Night blindness | Early sign | Often the first symptom parents report | | Bitot's spots | Conjunctival xerosis | Pathognomonic triangular foamy patches | | Corneal haziness/scarring | Progressive xerophthalmia | Leads to irreversible blindness | | Keratomalacia | Advanced stage | Corneal melting and perforation | | Follicular hyperkeratosis | Skin manifestation | "Goose skin" appearance | | Impaired immunity | Systemic effect | Increased susceptibility to infections (measles, diarrhea, pneumonia) | ### Why VAD Causes Blindness 1. Retinol is essential for synthesis of **11-cis retinal**, the visual pigment in rhodopsin 2. Deficiency leads to **xerophthalmia** (corneal drying and scarring) 3. Progressive stages: night blindness → conjunctival xerosis → corneal involvement → irreversible scarring and blindness ### Prevention & Management **Clinical Pearl:** WHO recommends high-dose vitamin A supplementation (200,000 IU) in children with measles or signs of VAD to reduce mortality by ~23% and prevent blindness. **Mnemonic:** **BITOT** = **B**lindness, **I**mmunity impaired, **T**eeth enamel defects, **O**phthalmologic signs, **T**eratogenic effects **High-Yield:** The WHO/UNICEF recommend universal vitamin A supplementation programs in countries with VAD prevalence >20% among children <5 years — this has dramatically reduced childhood blindness in endemic regions.