# To fit a contact lens to a patient's eye, a "keratometer" can be used to measure the curvature of the front surface of the eye, the cornea.

To fit a contact lens to a patient's eye, a "keratometer" can be used to measure the curvature of the front surface of the eye, the cornea. This instrument places an illuminated object of known size at a known distance p from the cornea. The cornea reflects some light from the object, forming an image of the object. The magnificationM of the image is measured by using a small viewing telescope that allows comparison of the image formed by the cornea with a second calibrated image projected into the field of view by a prism arrangement. Determine the radius of curvature of the cornea for the case p = 32.0 cm and M = 0.0150
cm

asked Apr 11, 2012 in Physics
reshown Jul 24, 2013

To solve this problem you need to use two equations.

The first is the equation for Magnification which is:

M = -q / p

and the second equation is the mirrior equation which is:

1/p + 1/q = 2/R

R is the radius of curvature, and q is the image distance.

First step is to solve for q, which is:

q = -M*p

Next, you can plug p and q into the mirror equation and solve for R.

R = 2/ (1/p + 1/q)

answered Apr 11, 2012 by ~Expert~ (3,856 points)
selected Apr 11, 2012 by awesome
Thanks!!!!!