If the refractive power of the unaccommodated eye of an emmetropic woman is 60 diopters (D), the axial length of her eye is closest to?
**Core Concept**
The refractive power of the eye is determined by the combination of the cornea, lens, and vitreous humor. In an emmetropic eye, the refractive power is balanced to focus light on the retina without any refractive error. The axial length of the eye is a critical factor in determining its refractive power.
**Why the Correct Answer is Right**
The refractive power of the eye is given by the formula: Refractive Power = (n2 - n1) / R, where n1 and n2 are the refractive indices of the media in contact with the lens, and R is the radius of curvature of the lens. In an emmetropic eye, the refractive power is approximately 60 diopters. The axial length of the eye is directly related to the refractive power, with longer eyes having lower refractive power and shorter eyes having higher refractive power. The normal axial length of an adult human eye is approximately 24 mm.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too short for an emmetropic eye. The axial length of an emmetropic eye is typically longer than 22 mm.
**Option B:** This option is incorrect because it is too long for an emmetropic eye. The axial length of an emmetropic eye is typically shorter than 26 mm.
**Option D:** This option is incorrect because it is not a plausible value for the axial length of an emmetropic eye.
**Clinical Pearl / High-Yield Fact**
A useful rule of thumb for estimating the axial length of an eye based on its refractive power is: Refractive Power (D) = 1 / (Axial Length (mm) / 6). This can be useful in clinical settings where the axial length is not directly measurable.
**Correct Answer:** C. 24 mm