**Core Concept**
Axial resolution in optical coherence tomography (OCT) refers to the ability of the imaging modality to distinguish between two closely spaced structures in the same axial plane. This is a critical parameter in OCT, which is widely used in ophthalmology and other medical specialties for imaging the retina and other tissues.

**Why the Correct Answer is Right**
The axial resolution in OCT is primarily determined by the coherence length of the light source used. A longer coherence length corresponds to a lower axial resolution, whereas a shorter coherence length allows for higher axial resolution. This is because the coherence length is inversely proportional to the bandwidth of the light source. A broader bandwidth results in a shorter coherence length, enabling higher axial resolution. In practice, the axial resolution of OCT is typically in the range of 5-15 μm.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the relationship between coherence length and axial resolution. A longer coherence length does not necessarily result in higher axial resolution.
* **Option B:** This option is incorrect because it suggests that the axial resolution of OCT is determined by the wavelength of the light source, rather than its coherence length. While wavelength does affect the penetration depth of the light, it is not the primary factor influencing axial resolution.
* **Option C:** This option is incorrect because it implies that the axial resolution of OCT is directly proportional to the coherence length, which is not the case.

**Clinical Pearl / High-Yield Fact**
When interpreting OCT images, it is essential to consider the axial resolution of the imaging modality, as it can significantly impact the ability to distinguish between different tissue structures.

**Correct Answer: C**. The axial resolution of optical coherence tomography is about 5-15 μm.