Question 1: Consider the following :
1. Night blindness
2. Corneal xerosis
3. Conjunctival xerosis
4. Keratomalacia
What is the correct sequence of the above in the progress of clinical presentation of vitamin A deficiency blindness?
- A. 1-3-2-4 (Correct Answer)
- B. 2-1-4-3
- C. 1-2-3-4
- D. 1-3-4-2
Explanation: ***1-3-2-4***
- This is the **correct sequence** according to WHO classification of xerophthalmia in vitamin A deficiency.
- **Night blindness (XN)** is typically the **earliest clinical manifestation**, resulting from impaired rod photoreceptor function due to insufficient rhodopsin synthesis.
- This is followed by **conjunctival xerosis (X1A)**, characterized by dryness and thickening of the bulbar conjunctiva, often accompanied by Bitot's spots (X1B) - foamy triangular patches of keratinized epithelium.
- As deficiency progresses, **corneal xerosis (X2)** develops, with dryness extending to the corneal surface, creating a hazy, lusterless appearance.
- The final and most severe stage is **keratomalacia (X3)**, involving corneal softening, ulceration, and potential perforation leading to irreversible blindness.
*2-1-4-3*
- This sequence incorrectly places **corneal xerosis** before **night blindness**.
- Night blindness is a functional symptom that appears early, while corneal xerosis is a later structural change.
- The progression also illogically places keratomalacia before conjunctival xerosis.
*1-2-3-4*
- This sequence incorrectly suggests **corneal xerosis** precedes **conjunctival xerosis**.
- In vitamin A deficiency, xerosis (dryness) affects the **conjunctiva first**, then progresses to involve the **cornea**.
- The conjunctiva is more susceptible to early changes than the cornea.
*1-3-4-2*
- This sequence incorrectly places **keratomalacia** before **corneal xerosis**.
- Keratomalacia represents corneal softening and melting, which cannot occur before the cornea becomes xerotic (dry).
- Corneal xerosis is a **prerequisite** for the development of keratomalacia.