A partially blind 84-year-old man suffering from Alzheimer’s miraculously survived a close encounter with a speeding No. 4 train after he wandered onto the tracks — walker and all — yesterday.

Anatoliy Zilberman lost several toes off his left foot and suffered severe bruising when the train nearly smashed into him on the express track just north of Union Square, police said.

Police are unsure how Zilberman, who lives in an assisted-living facility for the blind with his wife on East 23rd Street, ended up on the track and so deep in the tunnel.

Zilberman was taken to Bellevue Hospital, medical staff said.

His home health aide said Zilberman had told his wife that he wanted to go out for a walk and then vanished.