when you bought your topiary, if it was sheared tight, then the leaves dropping would be natural. the lack of light to the inner leaves would cause this. as long as you have a good thickness of outer growth you are fine. do you have much new growth occuring?

Hi -- this may be due to the shock of being transplanted. You didn't mention when it was done. Keep it in indirect sunlight for the meantime until it recovers. Don't overwater. Also you might look into some fertilizer for transplants.
Don't worry it will do fine.

Ianna