Angular conjunctivitis is usually caused by?
**Core Concept**
Angular conjunctivitis, also known as angular blepharitis, is a common condition characterized by inflammation of the conjunctiva and eyelids at the medial and lateral canthi. This condition is often associated with meibomian gland dysfunction, which leads to an imbalance in the tear film and promotes the growth of pathogenic microorganisms.
**Why the Correct Answer is Right**
The correct answer is **Staphylococcus aureus**. This bacterium is a common cause of angular conjunctivitis due to its ability to colonize the meibomian glands and produce lipase, which breaks down the lipid layer of the tear film. The resulting inflammation and infection lead to the characteristic symptoms of angular conjunctivitis, including redness, swelling, and discharge.
**Why Each Wrong Option is Incorrect**
**Option A:** Haemophilus influenzae is a bacterium that can cause conjunctivitis, but it is more commonly associated with purulent conjunctivitis in children, particularly those with underlying immune deficiencies.
**Option B:** Pseudomonas aeruginosa is an opportunistic pathogen that can cause conjunctivitis, particularly in contact lens wearers, but it is not typically associated with angular blepharitis.
**Option C:** Moraxella lacunata is a Gram-negative rod that can cause conjunctivitis, but it is not a common cause of angular conjunctivitis.
**Clinical Pearl / High-Yield Fact**
Meibomian gland dysfunction is a key underlying factor in the development of angular conjunctivitis. This is often due to a combination of factors, including age, sex, and genetic predisposition.
**Correct Answer:** C. Moraxella lacunata