To fit a contact lens to a patient?s eye, a keratometer can be used to measure t

Question

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 magnification M 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 = 29.0 cm and M = 0.0110. _______ cm

Explanation / Answer

M= 0.0110
distance of object = 29.0 cm

M = - di/ do
0.0110 = - di/29

di = - 0.319 cm

Focal length(f) = r/2
where r - radius of curvature.

1/f = 1/di + 1/d0

2/r = - 1/0.319 + 1/29

2/r = 0.0345 - 3.135

r = - 0.645 cm

Radius of curvature of cornea =  - 0.645 cm

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