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 = 31.0 cm and M = 0.0160. mm

Explanation / Answer

M = - q / p = 0.016

q = - 0.016p = - 0.016 x 31 = - 0.496 cm

1/f = 1/p + 1/q

1/f = 1/31 - 1/0.496

f = -0.504 cm   

R = 2f = 1.01 cm OR 10.1 mm .........Ans

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