This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
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? 
Select and explain. 
A. 14.5mm, B. 15.5mm, C. 16.5mm, D. 17.5mm
C: 16.5mm
Answer: C: 16.5mm 
Explanation: The focal point of an optical system (in meters) is the reciprocal of the refractive power of the system. Therefore, the focal point is 1/60 diopter (D), or 16.7 mm. An emmetropic eye forms a focused image of a distant object on the retina without accommodation. If the axial length is 16.5 mm, the image will be focused on the retina. Ref: Chang D.F. (2011). Chapter 2. Ophthalmologic Examination. In P. Riordan-Eva, E.T. Cunningham, Jr. (Eds), Vaughan & Asbury's General Ophthalmology, 18e.