In the Reduced Eye model, what is the cornea to anterior focal point distance according to Knapp's law?

• A. 16.67 mm
• B. 20.00 mm
• C. 12.50 mm
• D. 18.00 mm

Answer: (A)

In the reduced eye, Knapp's law uses the eye’s total optical power to set where the anterior focal point lies from the cornea. The reduced eye is modeled with a total power of about 60 diopters, so the focal length is f = 1/P = 1/60 meters ≈ 0.0167 meters, which is 16.7 mm. That is the distance from the cornea to the anterior focal point where parallel rays would first come to a focus. Therefore, about 16.7 mm is the correct distance. The other numbers would imply different overall powers for the reduced-eye model, not the standard 60 D used in Knapp’s law.