Thank you for attaching the images. They clearly show that your pear tree is infested with pear blister mites. These are very tiny mites, much different from the more common spider mites which you may be familiar with. Blister mites feed from the undersides of the leaves, beginning very early in the season, just as the leaves begin to unfurl. Their feeding causes reddish to yellowish green blisters which turn brown or black as the tissue dies later in the season. Leaves may drop prematurely.

Treatment is a late-dormant spray at the pre-pink stage, and a different dormant spray in the fall.  (See the information for pears in “Managing diseases and insects in home gardens,” pages 4 and 5; http://extension.oregonstate.edu/polk/sites/default/files/MG_Handouts/managing_diseases_and_insects_in_your_home_orchard_0.pdf. )