The posterior focal point of the reduced eye situated on the retina is how many millimetre behind the anterior surface of cornea:
**Core Concept**
The reduced eye is a simplified model used in optics to describe the eye's refractive powers. It is essential to understand the concept of focal points in the eye, as it relates to the accommodation mechanism and the optical properties of the eye.
**Why the Correct Answer is Right**
The posterior focal point of the reduced eye is the point at which parallel light rays converge after passing through the eye's refractive structures. In the reduced eye model, this point is located on the retina. The focal length of the reduced eye is approximately 17 mm, which corresponds to the distance between the anterior surface of the cornea and the posterior focal point. This is because the reduced eye model assumes a constant refractive power of the eye, which is not entirely accurate but provides a useful approximation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it suggests a focal point location that is too close to the anterior surface of the cornea, which would not be consistent with the eye's refractive properties.
**Option B:** This option is incorrect because it suggests a focal point location that is too far from the anterior surface of the cornea, which would not be consistent with the eye's optical properties.
**Option C:** This option is incorrect because it suggests a focal point location that is not on the retina, which contradicts the definition of the posterior focal point in the reduced eye model.
**Clinical Pearl / High-Yield Fact**
The reduced eye model is a useful tool for understanding the optical properties of the eye, but it should be noted that the actual eye has a more complex refractive structure, with varying refractive powers across different parts of the eye.
**Correct Answer:** C. 17 mm