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

Question

Q: To fit a contact lens to a patient's eye,a keratometer can be used to measure thecurvature of the cornea-the front surface of the eye. Thisinstrument places an illuminated object of known size at a knowndistance p from the cornea, which then reflectssome light from the object, forming an image of it. Themagnification Mof the image is measured by using asmall viewing telescope that allows a comparison of the imageformed by the cornea with a second calibrated image projected intothe field of view by a prism arrangement. Determine the radius ofcurvature of the corneawhen p = 32.0 cmand M = 0.0170. Q
mm
Q
mm

Explanation / Answer

Given :         Objectdistance   P = 32 cm         Magnification  M = - Q / P = 0.0170          Image distance Q   = - 32 * 0.0170 = - 0.544 cm We know that :       1 / f   = 1/P   + 1/ Q               = 1 / 32   - 1 / 0.544       f    = - 0.553 cm We have :           Radius of curvature   R = 2 f  = 2 * -0.553                                                            = - 1.106 cm                                                           = - 11.06 mm Hope this helps u!

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