**Core Concept**
Heterophoria is a type of eye deviation that is only visible when binocular vision is interrupted, such as when one eye is covered. Evaluating heterophoria involves assessing the alignment of the eyes and the extraocular muscles' function.

**Why the Correct Answer is Right**
To determine the correct answer, we must consider the methods used to evaluate heterophoria, including cover-uncover test, alternate cover test, and Maddox rod test.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is often related to assessing eye movements.
**Option B:** This might involve evaluating the extraocular muscles.
**Option C:** Could be about the cover-uncover test, commonly used for heterophoria.

**Clinical Pearl / High-Yield Fact**
A key point in evaluating heterophoria is the distinction between orthophoria, where the eyes are properly aligned, and heterophoria, where there's a latent deviation only seen when binocular vision is disrupted.

**Correct Answer: D.**