JI Packer's publisher Crossway announced the author, who was given the diagnosis over Christmas, is now unable to read or write.
The author of Christian bestseller Knowing God has lived with the same disease in his left eye for over a decade. The preacher was born in Gloucester, England but has lived in Canada since 1979.
In an interview published on The Gospel Coalition, Packer talked about "the sovereignty of God" and quoted Job chapter one: "The Lord gives and the Lord takes away".
"Now that I'm nearly 90 years old he's taken away. And I won't get any stronger, physically, as I go on in this world. And I don't know how much longer I'll be going on anyway" he said.
"God has been very good to us, and none of us has been struck as so many people of our age by any form of dementia. We're both blessedly free of that. You recognize this is a mercy and be thankful."
"You get old, and getting old means the loss of faculties and powers you had when you were younger. And that is the way God prepares us to leave this world for a better world to which he's taking us."
Crossway's Justin Taylor said the news marks "the end of a remarkable writing and speaking ministry".
Packer was recently recognised as one of the 20th century's "greatest theologians" by Crossway. The publisher praised him for his "steady, albeit generally quiet, influence on contemporary Evangelicalism".