Mizutani started having problems seeing the ball roughly 1 year ago. If people remember, he first played with sunglasses on at the WTTC 2018. He first revealed his problem in an interview with Table Tennis Report(Butterlfy's magazine) in Feb, 2019. He then went over the details in another interview with Rallys just a week ago, which got widely reported.
His left eye started deteriorating in 2014 and he had Lasik. Then last year, his right eye got worse as well all of a sudden and this time the Lasik didn't help much. He went to the US for consultation and the issue he can't see the ball isn't related to the Lasik. Mizutani says he can't see the ball under certain conditions, particularly with stage lighting and LED billboards. Now, he's only able to play at 30%, and 50% with glasses on.