**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 in the retina, primarily affecting the rod cells.

**Why the Correct Answer is Right**
Retinitis pigmentosa is often inherited in an autosomal dominant pattern, although other inheritance patterns can occur. The disease is caused by mutations in genes responsible for encoding proteins essential for photoreceptor cell function, such as rhodopsin. The degeneration of photoreceptor cells in RP leads to a loss of rod and cone cells, resulting in night blindness, peripheral vision loss, and eventually, central vision loss.

**Why Each Wrong Option is Incorrect**
**Option A:** RP is characterized by **degeneration of the photoreceptor cells**, not an increase in their number. Incorrect because RP is a degenerative disease.
**Option B:** RP is **not** typically associated with an increase in intraocular pressure, as this is more characteristic of glaucoma. Incorrect because RP is not typically associated with glaucoma.
**Option C:** RP **does** often involve **night blindness** as an early symptom, due to the degeneration of rod cells. Incorrect because this statement is true for RP.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of RP is the **"bone spicule" appearance** of the retinal pigment epithelium, which can be observed during a fundoscopic examination.

**Correct Answer:** A. RP is characterized by degeneration of the photoreceptor cells, not an increase in their number.