Pin hole can reduce refractive error upto -: (A) 1 D, (B) 3 D, (C) 5 D, (D) 10 D
Answer is B. Looking through a pinhole reduces the patients refreactive error and improves vision by increasing depth of focus. However, the pinhole vision is limited by diffraction. The opitimal apeure size of a pinhole is 1.2mm, which may correct up to 3D of refreactive error. Reference : Essentials of ophthalmology by Kaiser p.20