**Core Concept**
The net power of the cornea refers to its total refractive power, which is crucial for maintaining clear vision. The cornea's refractive power is determined by its curvature and the refractive indices of its components, including the epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. A precise balance of corneal power is essential for normal vision.

**Why the Correct Answer is Right**
The cornea's net power is approximately +48 diopters (D), making it the primary refractive surface of the eye. This value is achieved through the combination of the cornea's curvature and the refractive indices of its various layers. The cornea's high refractive power is essential for correcting vision and is a key factor in the development of myopia (nearsightedness) when the eye grows too long.

**Why Each Wrong Option is Incorrect**

* **Option A:** This value is incorrect as the cornea's net power is not +12 D; it is significantly higher.
* **Option B:** The cornea's net power is not +72 D; this value is too high and would not be physiologically consistent with human vision.
* **Option C:** This value is incorrect as the cornea's net power is not -12 D; it is positive due to its refractive properties.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the cornea's refractive power is highly dependent on its curvature, which can be altered through surgical procedures like radial keratotomy or LASIK. This highlights the importance of precise corneal power calculations in ophthalmic surgery.

**Correct Answer: C. -12 D**