Direct distant ophthalmoscopy is done from a distance of:
## **Core Concept**
Direct distant ophthalmoscopy is a technique used for examining the retina and other structures at the back of the eye. It involves using an ophthalmoscope to view the eye's interior. The distance at which this examination is performed is crucial for obtaining a clear view.
## **Why the Correct Answer is Right**
The correct distance for direct distant ophthalmoscopy is **25 cm**. At this distance, the examiner can properly align the ophthalmoscope with the patient's eye to visualize the retina. This technique allows for a wider field of view compared to indirect ophthalmoscopy but provides a more magnified image than direct ophthalmoscopy performed at a closer range.
## **Why Each Wrong Option is Incorrect**
- **Option A:** 10 cm - This distance is too close for direct distant ophthalmoscopy. It's more suitable for a slit-lamp examination or a detailed assessment that requires closer inspection.
- **Option B:** 50 cm - This distance is too far for direct ophthalmoscopy. At 50 cm, the examiner would not be able to focus on the structures at the back of the eye effectively.
- **Option D:** 50 cm - This option repeats the same incorrect distance mentioned in Option B and is therefore also incorrect.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that direct ophthalmoscopy, when performed at the correct distance, allows for a **red reflex** to be visible. This reflex is a critical indicator that the line of sight is properly aligned with the patient's pupil, guiding the examiner to the correct position for a thorough retinal examination.
## **Correct Answer:** . 25 cm