**Core Concept**
Bipolar cells are a type of interneuron found in the retina, playing a crucial role in processing visual information. They receive input from photoreceptors (rods and cones) and transmit signals to ganglion cells, which ultimately send visual information to the brain.

**Why the Correct Answer is Right**
Bipolar cells are characterized by their unique morphology, with a single dendrite that receives input from a photoreceptor and a single axon that synapses with a ganglion cell. This direct connection enables bipolar cells to amplify and modulate visual signals, allowing for more nuanced and detailed perception. The primary function of bipolar cells is to integrate and transmit visual information, making them essential for normal vision.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because bipolar cells are a specific type of interneuron found in the retina, whereas the other options are not directly related to retinal structure or function.
**Option B:** This option is incorrect because it does not accurately describe the location or function of bipolar cells.
**Option C:** This option is incorrect because it is a type of retinal cell that is involved in a different aspect of visual processing.

**Clinical Pearl / High-Yield Fact**
Bipolar cells are often referred to as the "interneurons of the retina" due to their role in processing and transmitting visual information between different layers of the retina.

**Correct Answer: D**