**Question:** The commonest cause of hypopyon is:

A. Trauma
B. Septic uveitis
C. Tuberculosis
D. Vitreous hemorrhage

**Core Concept:** Hypopyon refers to the presence of an inflammatory exudate in the anterior chamber of the eye, typically associated with an increased risk of infection and vision impairment.

**Why the Correct Answer is Right:** Bacterial endophthalmitis, also known as septic uveitis, is the most common cause of hypopyon. In this condition, bacteria invade the eye through various routes, such as trauma or systemic infections, and trigger an inflammatory response within the eye. One of the key features of septic uveitis is the presence of hypopyon, which is a result of the increased influx of white blood cells, proteins, and other cellular debris into the anterior chamber.

**Why Each Wrong Option is Incorrect:**

A. Trauma (Option A) is a potential cause of hypopyon, but it is less common compared to septic uveitis. Trauma-induced hypopyon usually resolves with topical antibiotics and supportive care.

C. Tuberculosis (Option C) is a possible cause of hypopyon in endemic regions, but it is less common in developed countries. Hypopyon in tuberculosis is usually associated with more severe ocular involvement and systemic manifestations.

D. Vitreous hemorrhage (Option D) is characterized by blood accumulation within the vitreous cavity, which is distinct from hypopyon. Hypopyon is typically accompanied by inflammation, whereas a vitreous hemorrhage is a result of blood leakage into the vitreous humor.

**Clinical Pearl:** Hypopyon should prompt a thorough investigation for the underlying cause, such as septic uveitis, to ensure appropriate treatment and prevent vision loss or blindness. Prompt diagnosis and treatment of septic uveitis can lead to a favorable prognosis for vision and eye health.