**Core Concept**
The question is testing the relationship between the axial length of the eyeball and its refractive power. The axial length is a critical factor in determining the refractive power of the eye, as it affects the focal length of the eye's optical system.

**Why the Correct Answer is Right**
For every 1mm change in the axial length of the eyeball, there is a corresponding change in the refractive power of the eye. This is because the refractive power of the eye is directly proportional to the axial length. The lens and cornea contribute to the refractive power of the eye, but the axial length is the primary factor. The correct answer is based on the concept of the eye's optical system and how changes in axial length affect its refractive power.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the relationship between axial length and refractive power is not linear, and a 1mm change does not produce a 1% change in refractive power.
**Option B:** Incorrect because a 1mm change in axial length would not produce a 0.5% change in refractive power; the correct answer is a different value.
**Option C:** Incorrect because the relationship between axial length and refractive power is not directly related to the power of the lens in diopters.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that a 1mm change in the axial length of the eyeball can lead to significant changes in refractive power, which can result in myopia or hyperopia. This is a critical concept in ophthalmology and optometry.

**Correct Answer: D. 4%**