## **Core Concept**
Retinitis pigmentosa (RP) is a group of genetic disorders affecting the retina's ability to respond to light, leading to progressive vision loss. It primarily affects the rod cells, which are responsible for peripheral and night vision. The condition results from mutations in genes that encode proteins crucial for photoreceptor function and survival.

## **Why the Correct Answer is Right**
The correct answer, **night blindness**, is the earliest symptom of retinitis pigmentosa because RP initially affects the rod cells. Rod cells are more numerous in the peripheral retina and are responsible for vision in low light conditions. Damage to these cells leads to difficulty seeing in the dark or at night, which is known as night blindness. This symptom precedes other visual disturbances such as loss of peripheral vision.

## **Why Each Wrong Option is Incorrect**
- **Option A: Loss of central vision** - This is incorrect because central vision, which is mediated by cone cells, is typically preserved until later stages of retinitis pigmentosa. Cone cells are more concentrated in the macula and are responsible for sharp, central vision.
- **Option B: Photophobia** - This is incorrect because photophobia, or sensitivity to light, is not a characteristic early symptom of RP. While some patients might experience discomfort in bright light, night blindness is the hallmark early symptom.
- **Option C: Blurred vision** - This is incorrect as an early symptom because blurred vision can occur in many conditions and is not specific or early for RP. Early RP primarily affects peripheral and night vision.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl for retinitis pigmentosa is that it often presents with a triad of **night blindness**, **peripheral vision loss**, and **abnormal electroretinogram (ERG)** findings. Early diagnosis can significantly impact management and genetic counseling.

## **Correct Answer:** . night blindness