**Core Concept**
Direct ophthalmoscopy is a technique used to examine the retina, macula, and optic disc in the living eye. It involves the use of a direct ophthalmoscope, a handheld instrument that allows the examiner to visualize the internal structures of the eye.

**Why the Correct Answer is Right**
Direct ophthalmoscopy is a widely used and essential tool in ophthalmology for assessing the posterior segment of the eye. The examiner holds the direct ophthalmoscope close to the patient's eye, and the light from the instrument is focused through the pupil, allowing the examiner to visualize the retina, macula, and optic disc in detail. This technique is particularly useful for detecting retinal pathologies, such as retinal detachments, macular edema, and optic disc drusen.

**Why Each Wrong Option is Incorrect**
**Option A:** Retinoscopy is a technique used to measure the refractive error of the eye and is not used for examining the internal structures of the eye.

**Option B:** Indirect ophthalmoscopy is a technique used to examine the peripheral retina and is typically performed using a condensing lens and an indirect ophthalmoscope, which provides a wider field of view than direct ophthalmoscopy.

**Option D:** Oblique illumination test is a technique used to examine the cornea and is not used for examining the internal structures of the eye.

**Clinical Pearl / High-Yield Fact**
Direct ophthalmoscopy is a critical skill for ophthalmologists and optometrists to master, as it allows for early detection and diagnosis of retinal pathologies that can lead to vision loss if left untreated.

**✓ Correct Answer: C. Direct ophthalmoscopy**