## **Core Concept**
Optic neuritis refers to inflammation of the optic nerve, which can cause sudden vision loss, pain on eye movement, and tenderness to the touch. This condition is often associated with demyelinating diseases like multiple sclerosis. The key clinical features involve visual disturbances.

## **Why the Correct Answer is Right**
The correct answer, **. Decreased visual acuity**, is right because optic neuritis primarily affects the optic nerve, leading to a reduction in visual acuity. This condition results from demyelination and inflammation of the optic nerve, disrupting the transmission of visual signals from the eye to the brain.

## **Why Each Wrong Option is Incorrect**
- **Option A: Increased intraocular pressure** - This is incorrect because optic neuritis does not directly cause an increase in intraocular pressure. Increased intraocular pressure is more commonly associated with conditions like glaucoma.
- **Option B: Papilledema** - This is incorrect because papilledema, or swelling of the optic disc, is typically associated with increased intracranial pressure, not optic neuritis. While both conditions affect the optic nerve head, their causes and clinical presentations are different.
- **Option D: Diplopia** - This is incorrect because diplopia, or double vision, is more commonly associated with disorders affecting the extraocular muscles or the nerves controlling them (III, IV, VI), not the optic nerve itself.

## **Clinical Pearl / High-Yield Fact**
A memorable point for exams is that optic neuritis often presents with **pain on eye movement** and **visual loss**, and it is a common presenting feature of **multiple sclerosis**. Remember, the presence of pain with eye movement in a young adult with visual symptoms should raise suspicion for optic neuritis.

## **Correct Answer: C. Decreased visual acuity**