**Core Concept**
Distance direct ophthalmoscopy is a technique used in ophthalmology to visualize the fundus of the eye. The distance between the patient's eye and the ophthalmoscope is critical to obtain a clear and accurate view of the retina.

**Why the Correct Answer is Right**
The correct distance for distant direct ophthalmoscopy is typically between 25-30 cm. This distance allows the ophthalmoscope to focus on the fundus, and the patient's eye to be in the optimal position for examination. The cornea and lens of the eye work together to refract light, and at this distance, the ophthalmoscope can capture the image of the retina without any significant distortion.

**Why Each Wrong Option is Incorrect**
**Option A:** 10 cm is too close, and the image would be severely distorted due to the magnification of the ophthalmoscope.
**Option B:** 50 cm is too far, and the image would be out of focus due to the lack of optimal refractive power.
**Option C:** 15 cm is still too close, and the cornea and lens would not be able to refract light properly for a clear image.

**Clinical Pearl / High-Yield Fact**
To remember the correct distance for distant direct ophthalmoscopy, recall the phrase "25-30 cm, the perfect view". This will help you associate the correct distance with a clear and accurate view of the fundus.

**Correct Answer: D. 25-30 cm**