**Core Concept**
The Listing's Reduced eye is an anatomical model used in ophthalmology to simplify the complex structure of the human eye. It is used to calculate the power of the lens required for vision correction. The distance between the nodal point and the cornea is an important parameter in this model.

**Why the Correct Answer is Right**
In the Listing's Reduced eye, the distance between the nodal point and the cornea is calculated to be 17mm. This value is used to determine the power of the lens required for vision correction. The nodal point is the point on the optical axis where the angle of incidence equals the angle of emergence, and it is an important concept in understanding how the eye focuses light.

**Why Each Wrong Option is Incorrect**
**Option A:** 15mm - This value is incorrect because it is not the standard distance between the nodal point and the cornea in the Listing's Reduced eye.
**Option B:** 20mm - This value is also incorrect because it is greater than the standard distance and would not be used in calculating the power of the lens required for vision correction.
**Option C:** 25mm - This value is incorrect because it is significantly greater than the standard distance and would not be used in any calculation related to the Listing's Reduced eye.

**Clinical Pearl / High-Yield Fact**
The Listing's Reduced eye is a simplified model of the human eye and is used to calculate the power of the lens required for vision correction. It is an important concept in ophthalmology and should be remembered by students and practitioners alike.

**Correct Answer:** D. 17mm