You made the assumption for a lens in air. The eye is not a lens "in air".

Thank you, Otis, for posting that link to exactly what I’ve been looking for. I see that the calculation you present yields a focal power of 57 diopters, which I consider to be in agreement with the statement in

http://en.wikipedia.org/wiki/Diopter#In_vision_correction that the optical power of the relaxed eye is approximately 60 dioptres. You used the following equation:

*Focal Power = (Refractive Index) / (Focal Length)*

However, according to

http://en.wikipedia.org/wiki/Focal_power, focal power is defined as the reciprocal of the focal length, i.e.,

*Focal Power = 1 / (Focal Length)*

So we now have a pair of conflicting definitions. How do we resolve that? And how is the lens being in air or not relevant?