WHO Is Staging of Vitamin A Deficiency?

October 17, 2025 •

3 min read

According to the World Health Organization (WHO), vitamin A deficiency is a significant public health problem in more than half of all countries, especially in Africa and South-East Asia. The formal staging of vitamin A deficiency, particularly the ocular manifestations, is standardized by the WHO to help clinicians and public health professionals assess the severity and implement appropriate interventions. This system provides a crucial framework for diagnosis, treatment, and global health monitoring.

Quick Summary

The World Health Organization (WHO) provides a standardized staging system for vitamin A deficiency, primarily based on the spectrum of ocular signs known as xerophthalmia. This classification ranges from night blindness to severe corneal damage and irreversible blindness. Subclinical deficiency is also assessed via serum retinol levels. These classifications are vital tools for healthcare practitioners and public health programs worldwide.

Key Points

WHO Framework: The World Health Organization (WHO) is staging of vitamin A deficiency through a standardized classification system, primarily centered on ocular signs called xerophthalmia.
Clinical vs. Subclinical: The system recognizes both visible clinical signs (xerophthalmia) and subclinical deficiency, which is detected via low serum retinol levels.
Ocular Progression: Clinical staging follows a clear progression, starting with night blindness (XN) and progressing through stages of conjunctival and corneal dryness to severe ulceration (keratomalacia, X3B).
Irreversible Damage: Severe, untreated VAD can lead to permanent corneal scarring (XS) and irreversible blindness, highlighting the importance of early diagnosis.
Global Public Health Tool: The WHO classification helps international bodies, governments, and health programs monitor VAD prevalence, allocate resources, and measure the impact of interventions.
Prevention is Key: Staging informs prevention strategies like targeted vitamin A supplementation programs and food fortification initiatives in at-risk populations.

Understanding the WHO's Role in Staging

The World Health Organization (WHO) has long been instrumental in defining and monitoring nutritional deficiencies, including vitamin A deficiency (VAD). The WHO's staging system is internationally recognized, providing a consistent framework for assessing VAD's clinical and public health significance. It differentiates between subclinical deficiency, characterized by low serum levels without visible signs, and clinical deficiency, which manifests through distinct eye signs known as xerophthalmia. This standardization is crucial for global reporting, resource allocation, and targeted interventions in vulnerable populations.

The WHO's system uses codes to denote the severity of xerophthalmia, aiding diagnosis and treatment. This helps healthcare workers, especially in resource-limited settings, to identify cases early and prevent permanent vision loss. The WHO also sets population-level prevalence cut-off points, which guide governments and international bodies in determining the public health severity of VAD.

The Clinical Stages of Xerophthalmia

The WHO's clinical staging of VAD, or xerophthalmia, is based on observable eye signs that indicate increasing deficiency severity. This staging is key for clinical practice in areas where VAD is common.

Stage XN: Night Blindness

Night blindness (XN) is the earliest and most common ocular symptom, involving difficulty seeing in dim light due to impaired rod cell function.

Stage X1A/X1B: Conjunctival Xerosis and Bitot's Spots

Progression can lead to dry conjunctiva (conjunctival xerosis, X1A), where the eye surface becomes rough. Further deficiency can cause Bitot's spots (X1B), which are foamy patches on the conjunctiva.

Stage X2: Corneal Xerosis

Worsening deficiency affects the cornea, causing corneal xerosis (X2), where the cornea becomes dry and dull.

Stage X3A/X3B: Corneal Ulceration and Keratomalacia

This severe stage involves corneal ulceration (X3A). If the ulcer is large (one-third or more of the cornea), it is termed keratomalacia (X3B), leading to softening and potential perforation, and a high risk of permanent blindness.

Stage XS: Corneal Scars

Corneal scarring (XS) is the irreversible result of severe corneal damage, causing permanent vision loss.

Stage XF: Xerophthalmic Fundus

Rarely, chronic cases show changes in the back of the eye (xerophthalmic fundus, XF) as white lesions, though this typically doesn't cause blindness.

Comparison of Clinical and Subclinical VAD Assessment

Both clinical signs and subclinical indicators are necessary for managing VAD. The table below compares these assessment methods.


Feature	Clinical Assessment (Xerophthalmia Staging)	Subclinical Assessment (Serum Retinol)
Method	Physical eye examination.	Laboratory blood test.
Indicators	Night blindness, Bitot's spots, corneal damage.	Serum retinol levels: <0.70 µmol/L (subclinical) and <0.35 µmol/L (severe) in children.
Reflects	Acute or chronic severe deficiency with visible damage.	Overall vitamin A status, but less sensitive to moderate depletion.
Strengths	Diagnoses late-stage deficiency; easily observable.	Objective measure for population risk and milder deficiency.
Limitations	Misses milder cases; signs may persist after treatment.	Serum levels are affected by inflammation and liver stores.

Conclusion

Effective VAD management and prevention require a comprehensive approach using both clinical staging and subclinical assessment. The WHO's standardized xerophthalmia staging system is vital for identifying and classifying the severity of eye manifestations, enabling targeted treatment and preventing blindness. However, as clinical signs represent the most severe cases, subclinical assessment like serum retinol testing is crucial for population-level monitoring. Combating VAD necessitates sustained public health efforts through supplementation, dietary improvements, and surveillance, guided by the WHO's internationally recognized criteria.

For more information on global efforts against VAD, consult the WHO's official website: (https://www.who.int/nutrition/publications/micronutrients/vitamin_a_deficiency/en/).

Lists of WHO classifications for clinical VAD

XN: Night blindness.
X1A: Conjunctival xerosis.
X1B: Bitot's spots.
X2: Corneal xerosis.
X3A: Corneal ulceration.
X3B: Keratomalacia.
XS: Corneal scars.
XF: Xerophthalmic fundus.

Lists of Risk Factors for VAD

Inadequate Dietary Intake.
Malabsorption Syndromes.
Increased Physiological Demand.
High Rates of Infection.
Liver Disease.

Lists of Prevention Strategies

Supplementation Programs.
Food Fortification.
Dietary Diversification.
Health Education.
Disease Control.

Frequently Asked Questions

The official staging system by the WHO is based on the classification of xerophthalmia, the term for the eye manifestations of vitamin A deficiency.

Young children and pregnant women in low-income countries are at the highest risk due to inadequate dietary intake and higher physiological demands.

Yes, night blindness (XN) is one of the earliest signs and is often reversible with prompt vitamin A supplementation.

Xerophthalmia is the umbrella term for all eye problems related to VAD. Keratomalacia is the most severe form, involving the irreversible softening and ulceration of the cornea.

Subclinical deficiency is identified by measuring serum retinol concentrations. A level below 0.70 µmol/L in children indicates a deficiency.

The liver stores a large portion of the body's vitamin A. Serum retinol levels are maintained by these stores, so a significant depletion of liver reserves is required before serum levels drop noticeably.

While the primary staging system focuses on eye signs, the WHO acknowledges other consequences of VAD, such as increased risk of infection, anemia, and impaired growth.