Dear Ace,

Here are the basic equations of physiological
optics.  If you assume that the eye
is a "box camera" (Gullistrand model)
the calculations are quite simple.

(From Chapter 3 my book)

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BASIC OPTICAL PHYSICS

In order to understand the design and behavior of the normal eye it is
necessary to understand its basic optical properties.

When a light ray enters water it is refracted (bent). The equation that
describes this bending is shown below. Water has an Index-of-Refraction
of 1.33. The normal eye has 1.38 as an over-all Index-of-Refraction.
(Figure 1)

SNELL'S LAW OF REFRACTION

Figure 1.

When light travels through a curved surface, the light rays converge on
a single point. Since an image is made up of a large number of points
of light, an image will form where the light rays converge. (Figure 2)

THE APPROXIMATE REFRACTIVE CHARACTERISTIC OF THE EYE

Figure 2 (from Gullstrand's schematic eye, Reference 1).

The distance between the surface of the lens and the point of image
formation is called the focal length.

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

By using this equation it is possible to analyze the basic optical
properties of the eye. The approximate dimensions of the eye have been
established. The radius of the cornea is 0.66 centimeters, the index of
refraction is 1.38, and the length of the eye is 2.4 centimeters. By
using these numbers we can calculate the focal power of the normal eye.
(For reasons of clarity, I have not included the effect of the internal
lens. A more detailed analysis can be found in Reference 1.)

Focal Power = 1.38 / .024 Meters

Focal Power = 57 Diopters

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You can continue with these
calculations.  DrG and the
other ODs can confirm you
the formula and your math for you.

Best,

Otis