To fit a contact lens to a patient\'s eye, a keratometer can be used to measure

Question

To fit a contact lens to a patient's eye, a keratometer can be used to measure the curvature of the cornea-the front surface of the eye. This instrument places an illuminated object of known size at a known distance p from the cornea, which then reflects some light from the object, forming an image of it. The magnification M of the image is measured by using a small viewing telescope that allows a 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 when p = 29.0 cm and M = 0.0100.

mm

Explanation / Answer

We know that M = q/p

0.0100 = q/29

q = (29)(0.0100) = 0.29 Now find f using the lens formula f = pq/(p + q) = (0.29)(29)/ (0.29 + 29) = 0.28712871287 Since radius of curvature is half of the focal length so R = f / 2 = 0.14356435643cm

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