**Core Concept**
Angular conjunctivitis is a type of conjunctivitis characterized by inflammation of the conjunctiva at the medial and lateral canthi. The causative organisms are often related to poor hygiene and contamination of the ocular surface.

**Why the Correct Answer is Right**
The commonest causative organism for angular conjunctivitis is Haemophilus aegyptius, a Gram-negative coccobacillus. This bacterium is highly contagious and often spreads through direct contact with infected individuals or contaminated surfaces. The pathogenesis of angular conjunctivitis involves the colonization of the conjunctiva by H. aegyptius, leading to an inflammatory response and the characteristic symptoms of conjunctivitis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Pseudomonas aeruginosa is a Gram-negative rod that can cause various ocular infections, but it is not the most common causative organism of angular conjunctivitis.
* **Option B:** Staphylococcus aureus is a Gram-positive coccus that can cause conjunctivitis, but it is not the primary causative agent of angular conjunctivitis.
* **Option C:** Moraxella lacunata is a Gram-negative rod that can cause conjunctivitis, but it is not the most common causative organism of angular conjunctivitis.

**Clinical Pearl / High-Yield Fact**
Angular conjunctivitis is often associated with poor hygiene and is highly contagious, making it essential to practice good hand hygiene and avoid sharing personal items to prevent its spread.

**Correct Answer:** C.