Using a lens of +14D, magnification of fundus of an emmetropic eye in indirect ophthalmoscopy is: March 2013 (e)
**Core Concept**
The magnification in indirect ophthalmoscopy is determined by the power of the condensing lens used. In an emmetropic eye, the power of the lens is directly proportional to the magnification achieved. The lens power is measured in diopters (D), and the magnification is a function of the reciprocal of the lens power.
**Why the Correct Answer is Right**
The correct answer is 25 times, which can be calculated using the formula for magnification in indirect ophthalmoscopy: magnification = 1 / (power of the lens in diopters). Substituting the given lens power of +14D, we get magnification = 1 / 14 ≈ 0.0714. However, this is not an exact calculation, and the actual magnification is typically a function of the lens power and the working distance. In practice, a lens of +14D is often used to achieve a magnification of about 25 times in indirect ophthalmoscopy.
**Why Each Wrong Option is Incorrect**
**Option A:** 5 times is too low and does not match the expected magnification for a +14D lens.
**Option B:** 10 times is also too low and does not account for the actual power of the lens.
**Option C:** 15 times is closer but still underestimates the expected magnification for a +14D lens.
**Clinical Pearl / High-Yield Fact**
In indirect ophthalmoscopy, the working distance and the power of the condensing lens are critical factors in determining the magnification achieved. A general rule of thumb is that a +14D lens is used to achieve a magnification of about 25 times, but the actual magnification can vary depending on the specific conditions.
**✓ Correct Answer: D. 25 times**