**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 is characterized by degeneration of the photoreceptor cells (rods and cones) in the retina.

**Why the Correct Answer is Right**
The correct answer is related to the characteristic features of retinitis pigmentosa. RP is typically associated with night blindness, peripheral vision loss, and eventually central vision loss. However, the correct answer is related to another feature that is not typically seen in RP.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because RP is indeed associated with a decrease in the number of rod photoreceptors, which leads to night blindness.

**Option B:** This option is incorrect because RP is characterized by a loss of peripheral vision, which is often the first symptom.

**Option C:** This option is incorrect because RP is not typically associated with a significant increase in the number of melanin deposits in the retina.

**Why the Correct Answer is Right (Continued)**
However, the correct answer is actually related to the presence of **Option D:** Macular dystrophy. Macular dystrophy is a separate condition that affects the central retina, causing central vision loss, but it is not typically seen in retinitis pigmentosa.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that retinitis pigmentosa is a heterogeneous group of disorders, and the clinical presentation can vary depending on the specific genetic mutation.

**Correct Answer:** D. Macular dystrophy.