My vision blurrs after several minutes when reading with bifocals which I have read with for years and only recently am having the problem. I am 73. The longer I read, the worse it gets. The blurring lasts for at least an hour+ and affects both the reading and long distance through my normal distance part of my glasses. If I read without my bifocals, I have to put the readiing material very close and it is somewhat blurred. But, after I read w/o glasses for an hour, my vision, both near and far are normal with my glasses. My Opthomologist is perplexed by the problem, and I am going to try other experiments to see what the results are. I will read with a pair of distance glasses from at least an arms length and see if it creates any blurring. I am doing that right now and it does not seem to create any blurring. I then plan to cover one eye while reading with my bifocals and see what happens.