Bitot Spots: Signs, Microbiology, and Ocular Surface Care

Vitamin A deficiency can lead to serious eye complications, including the development of Bitot spots. These foamy, white lesions on the conjunctiva indicate prolonged deficiency and signal broader nutritional and ocular health concerns. Left untreated, they may contribute to further vision deterioration and eye dysfunction.

Understanding their formation, along with proper diagnostic methods and care strategies, is essential for preventing long-term damage.

Clinical Appearance and Conjunctival Changes

Bitot spots appear as foamy, whitish plaques on the bulbar conjunctiva, typically on the temporal side. These lesions form due to keratinized epithelial cells and bacterial overgrowth, primarily involving Corynebacterium xerosis. The conjunctiva, usually smooth and translucent, undergoes significant changes in chronic vitamin A deficiency. Goblet cell loss reduces mucin production, destabilizing the tear film and contributing to the dry, rough texture observed in affected areas. This disruption exacerbates keratinization, reinforcing the characteristic appearance of Bitot spots.

As deficiency progresses, the conjunctival epithelium thickens and becomes opaque. Histological examinations reveal hyperplasia of the stratified squamous epithelium, parakeratosis, and reduced epithelial turnover. These structural changes compromise the conjunctiva’s protective function, increasing susceptibility to secondary infections and mechanical irritation. Bitot spots often coincide with xerophthalmia, which includes conjunctival and corneal xerosis.

The texture and composition of Bitot spots vary with the severity and duration of deficiency. In early stages, they appear as small, irregular patches with a slightly raised surface. Over time, they enlarge and develop a plaque-like consistency due to progressive keratinization. Unlike other conjunctival abnormalities, Bitot spots do not dissolve with blinking or lubrication. In some cases, fine epithelial debris further contributes to the roughened ocular surface.

Ocular Surface Microbiology and Contributing Factors

The ocular surface microbiome plays a key role in the development and persistence of Bitot spots, particularly due to Corynebacterium xerosis. This Gram-positive bacterium, normally present on the conjunctiva, becomes opportunistic when ocular defenses are weakened. Vitamin A deficiency diminishes the protective mucin layer, creating conditions that favor bacterial colonization and biofilm formation. C. xerosis adheres to desquamated epithelial cells and thrives in a lipid-rich environment, reinforcing the keratinized plaques characteristic of Bitot spots.

Beyond C. xerosis, other commensal bacteria, such as Staphylococcus epidermidis and Propionibacterium species, become more prominent due to the disrupted tear film and epithelial barrier. Microbiome analyses of xerotic conjunctival surfaces show a decline in beneficial bacteria, correlating with increased colonization by keratinophilic organisms. Bacterial metabolites, including lipases and proteases, further promote epithelial desquamation and keratinization, altering the conjunctival microenvironment. Biofilm-like structures on the ocular surface contribute to the persistence of Bitot spots, making them resistant to simple removal or hydration.

Environmental and systemic factors also influence microbial dynamics. Poor hygiene, exposure to dust and pollutants, and inadequate tear production encourage bacterial persistence. In regions where vitamin A deficiency is prevalent, limited access to clean water and sanitation exacerbates ocular surface colonization by opportunistic microbes. Additionally, malnutrition and gastrointestinal infections impair vitamin A absorption, indirectly promoting conjunctival changes that favor bacterial overgrowth. These external and internal factors create a cycle where microbial proliferation reinforces epithelial deterioration, perpetuating Bitot spot formation.

Diagnostic Methods and Screening Considerations

Detecting Bitot spots relies on clinical evaluation, with slit-lamp biomicroscopy as the primary tool for assessing their foamy, plaque-like texture and keratinized composition. This method also helps evaluate associated conjunctival changes, such as xerosis and epithelial thickening. When the presentation is unclear, conjunctival impression cytology provides a more definitive assessment, revealing keratinized epithelial cells, goblet cell depletion, and bacterial colonization. This technique is particularly useful in early-stage cases.

Beyond direct examination, biochemical markers offer additional insights. Serum retinol levels below 0.70 µmol/L indicate vitamin A deficiency. While this test provides systemic confirmation, it is not always accessible in resource-limited settings. In such cases, functional assessments like the dark adaptation test can evaluate early ocular manifestations before structural damage occurs. This test measures the time required for vision to adjust to darkness, reflecting photoreceptor function, which depends on adequate vitamin A levels.

Screening programs targeting at-risk populations play a crucial role in early detection and prevention. Children under five, pregnant women, and individuals with malabsorption disorders are among the most vulnerable, necessitating routine ocular examinations in endemic regions. Community-based initiatives integrate clinical screening with nutrition assessments to identify deficiency-related complications before they become irreversible. Mobile health units and telemedicine platforms improve access to screening services, particularly in rural areas with limited ophthalmologic care. These programs help reduce the long-term burden of vitamin A deficiency and its ocular manifestations.

Approaches to Support Ocular Surface Health

Maintaining ocular surface integrity requires nutritional support, targeted interventions, and environmental modifications. Vitamin A supplementation is the most effective strategy for addressing deficiency-related conjunctival abnormalities. The World Health Organization (WHO) recommends high-dose vitamin A supplementation (200,000 IU for adults, 100,000 IU for infants, and 50,000 IU for neonates) to rapidly restore ocular health. This intervention has been shown to reduce xerophthalmia, including Bitot spots, by nearly 63% in at-risk populations. While supplementation provides immediate benefits, long-term dietary improvements are necessary to prevent recurrence. Foods rich in preformed vitamin A, such as liver, egg yolks, and dairy products, along with carotenoid sources like carrots, sweet potatoes, and dark leafy greens, help maintain adequate levels.

Optimizing tear film stability reduces conjunctival stress. Artificial tears with lipid-based formulations or carboxymethylcellulose improve epithelial hydration. Studies show that preservative-free lubricants enhance tear film breakup time and reduce ocular surface damage in chronic xerosis. In advanced conjunctival keratinization, retinoic acid eye drops have shown promise in reversing epithelial metaplasia by promoting normal conjunctival cell differentiation. Though not widely available, these topical formulations offer a targeted approach for restoring ocular surface homeostasis in severe deficiency-related conditions.