Station eight
(allowed 5 minutes)

aa
 a A security guard with 3 D of myopia in both eyes and 1.5D of accommodative amplitude  wants single vision glasses for viewing CCTV screen 1 m in front of him. a. if he is fully corrected for distance, at what distance can he see comfortably using his      accommodative reserve (assuming that he uses one-third of his accommodative reserve)? b. what power lenses should be given for him to see the CCTV comfortably (again assume      that he uses one-third of his accommodative reserve)?
a
 Answer to a As he uses 0.5D of accommodation (one-third of 1.5D), he would  be able to see 2 m in front of him comfortably when the eyes are fully corrected for distance.  f (focal length in metre) = 1 / D (power of lens in dioptre).   Answer to a The specified distance of 1 m is 1D from the patient (again using the  formula  f = 1/D). Because the patient can provide 0.5D, an  additional 0.5D is needed in the glasses. To meet the patient's need, the single vision glasses should be 2.5D ie. 3D - 0.5D = 2.5D