BBC Sport earlier incorrectly reported Ward had retired.
"Over the past week, I have received advice from three separate eye consultants," said Ward.
"They have all told me that I have suffered damage to the retina of my left eye and that this damage is partly irreversible.
"I may get some sight back, but this won't be a quick process, and whether it will be sufficient for me to get back to playing international hockey only time will tell.
"It is a tough pill to swallow but, as people know, I am not one to give up easily and I will do everything can to make myself available for selection for Tokyo."
GB Hockey says it will be a "number of months" before the extent of the damage to Ward's eye is known.
"Sam has suffered a very serious injury," said performance director Ed Barney.
"Our focus is on supporting Sam to the best possible extent and ensuring that he has access to the best medical provision and wider support. The players and staff wish Sam well during this challenging period."
Ward has scored 72 goals in 126 appearances for Great Britain and England.
He made his international debut in 2014 and represented Great Britain at the Rio 2016 Olympics, before helping England to European and Commonwealth Games bronze in 2017 and 2018 respectively.