While performing a right cataract operation, you inadvertently inserted a 25.00 D intraocular 
lens instead of a 20.50D (aiming for -0.05D) into the capsular bag.
 

a. Would the patient become more myopic or hypermetropic in the right eye?
 

The patient was unable to tolerate the anisometropia and found contact lens difficult to use. 
You performed a lens exchange and insert the new lens in the sulcus. Post-operatively, the 
patient's refraction was -0.50D. However, he returned two weeks  later, complaining of 
decreased vision. Repeated refraction showed that he had developed a 3.50D astigmatism.
 

b. What is the most likely cause for this change of refraction?