What is the total optical power of the eye in the Reduced Eye model (in diopters)?

What is the total optical power of the eye in the Reduced Eye model (in diopters)?

• A. +60D
• B. -60D
• C. +40D
• D. +20D

Answer: (A)

In the Reduced Eye model, the eye is treated as a single converging lens with a short focal length. The typical focal length is about 16.7 mm, so the optical power is P = 1/f ≈ 1 / 0.0167 m ≈ +60 diopters. This level of positive, high power is what brings parallel rays from distant objects to focus onto the retina, matching emmetropia in this simplified model. Powers like +40D or +20D would have longer focal lengths and wouldn’t place the image on the retina for distant objects, while a negative power would diverge light instead of converging it.

In the Reduced Eye model, the eye is treated as a single converging lens with a short focal length. The typical focal length is about 16.7 mm, so the optical power is P = 1/f ≈ 1 / 0.0167 m ≈ +60 diopters. This level of positive, high power is what brings parallel rays from distant objects to focus onto the retina, matching emmetropia in this simplified model. Powers like +40D or +20D would have longer focal lengths and wouldn’t place the image on the retina for distant objects, while a negative power would diverge light instead of converging it.