For seeing a clear image of an object eyes have to be very accurately aligned towards that object. if one of the eye is not able to do so than problems like double vision
, shadows, blurring etc can appear. If the mismatch is very little than our vision mechanism is able to compensate and blurring does not appear. However there are situations in which decompensation occurs and eyes which were otherwise well adjusted start having problems. Commonly such triggers are fever
etc. you might have had that 1 year back and that has caused the problems. Prism lenses and/ or surgery may be required for correction of this mismatch.