**Core Concept**
Refraction in ophthalmology refers to the bending of light as it enters the eye, which is crucial for vision. Accurate measurement of refraction is essential for diagnosing refractive errors such as myopia, hyperopia, and astigmatism. Objective tests of refraction are essential to avoid subjectivity and ensure accurate measurements.

**Why the Correct Answer is Right**
All the listed options are indeed objective tests of refraction. **Retinoscopy** is a widely used technique that involves shining a light into the eye and observing the reflection to determine the refractive error. **Refractometry** measures the refractive power of the eye by using a device that projects a series of rings onto the retina. **Keratometry** measures the curvature of the cornea, which is a critical component of the eye's refractive system. These tests are essential for ophthalmologists to accurately diagnose and correct refractive errors.

**Why Each Wrong Option is Incorrect**
**Option A:** While retinoscopy is an objective test, it is not the only one, so this option is partially correct but not entirely. However, since it's an option that is indeed correct, we can't say it's wrong.
**Option B:** Refractometry is not a commonly used term; however, it's implied by the term optometry or ophthalmometry which are used to measure the refractive power of the eye. This option could be misleading, but in the context of the question, it's a bit ambiguous.
**Option C:** Keratometry is indeed an objective test, but like retinoscopy, it's just one of the methods used to assess refraction.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that a comprehensive eye examination involves a combination of subjective and objective tests, including refraction, to accurately diagnose and manage various eye conditions.

**✓ Correct Answer: D. All the above**