**Core Concept**
Tuberculosis (TB) is a chronic bacterial infection caused by Mycobacterium tuberculosis, which can affect various parts of the body, including the eyes. In ocular tuberculosis, the choroid is the most commonly affected tissue, leading to inflammation and damage.

**Why the Correct Answer is Right**
Choroiditis is the commonest ocular manifestation of tuberculosis due to the hematogenous spread of the bacteria from the lungs to the eyes. The choroid, rich in blood vessels, provides an ideal environment for the growth of M. tuberculosis. The infection leads to inflammation of the choroid, causing symptoms such as pain, redness, and vision loss. The choroiditis can be granulomatous or exudative, with the former being more common in ocular TB.

**Why Each Wrong Option is Incorrect**
**Option A:** Phlyctenular conjunctivitis is a type of conjunctivitis characterized by the formation of small nodules on the conjunctiva, usually caused by an allergic reaction to staphylococcal toxins or other antigens. It is not a common manifestation of tuberculosis.
**Option C:** Eales' disease is a form of retinal vasculitis characterized by recurrent episodes of retinal hemorrhage and vitreous hemorrhage, often in young adults. While it can mimic ocular TB, it is not a manifestation of the disease.
**Option D:** Acute retinal necrosis is a severe inflammatory condition of the retina, often caused by viral infections such as herpes simplex or varicella-zoster. It is not associated with tuberculosis.

**Clinical Pearl / High-Yield Fact**
In ocular tuberculosis, the choroiditis can be confused with other conditions such as sarcoidosis or uveitis. A thorough medical history, including exposure to TB, and diagnostic tests such as imaging and biopsy, are essential for an accurate diagnosis.

**✓ Correct Answer: B. Choroiditis**