Marc Chiang cannot see his opponent on the other side of the court, or the ball until it is less than a metre away from him.
For that matter, he cannot even see where his own shots go.
The 38-year-old, who is partially blind, only knows he has kept the ball in play when he hears its distinctive rattle coming back towards him.
Listening is the most important skill in soundball, or blind tennis, as it is the players' only means of locating the sponge ball, which is filled with ball bearings.
Chiang's eyesight degenerated about seven years ago, when he was diagnosed with retinitis pigmentosa, a hereditary disorder that involves a breakdown and loss of cells in the retina.
"I have played tennis since I was 10, and tennis is such a three-dimensional game. So it was hard to adjust initially when you don't know how high or far away the ball is," said the engineer yesterday at the Pathlight School campus, where Soundball Singapore holds its weekly training sessions.
"But the better I got at listening to the ball, the more I could get over the frustration of not being able to see."
He is one of three Singaporeans headed to Dublin for the April 26-30 Dublin Takei International Blind Tennis Tournament, organised by the International Blind Tennis Association.
He finished fourth in the inaugural edition in Spain last year in the B2 (partially blind) category. About 70 players from 13 countries are expected to take part this year.
Joining Chiang will be Ong Hock Bee in the men's B1 (fully blind) category and Chris Tan in the women's B2 category. They will be accompanied by two volunteers.
Said Tan, 45, who is also the Soundball Singapore chairman: "I'm really excited (about going to Dublin). I know the standard is going to be very high and while I've improved, it's really just about going there to gain the experience.
"Soundball is becoming more popular and competitive internationally, and we hope to get more visually impaired people here to give it a try."