LONDON (REUTERS) - Smart glasses could transform the theatre experience for the deaf and hard-of-hearing.

Developed by Japanese firm Epson and UK computer scientists, they use augmented reality software to show subtitles synchronised with the actors' performances.

They've been launched at London's National Theatre.

Mr Jonathan Suffolk, technical director at the National Theatre, said: "Working with Professor Andrew Lambourne from Leeds Beckett University, he's developed a speech-following system that listens to the phonetics of the performers and we combine that with information that derived from the production environment, which is lighting cues, sound cues...

"And we create a file that's effectively a live way of triggering and broadcasting these captions to the glasses."

Each set is customisable, so you can change font size, colour and position.

And it's already helping theatregoers.

Mr Tim Hardy, a hard-of-hearing theatregoer who has been helping to test the glasses, said: "I used to buy the text every time and follow it with a torch on my lap.

"Captioning of all sorts being available makes a huge difference... It's interesting to see how easily the eye and the brain can actually absorb the text at the same time as the looking at the action on stage. It's a comfortable experience."

The current system sticks rigidly to the play's text.

But future versions could adjust itself if there's an unplanned deviation.

Said Mr Suffolk: "The system delivers the script that's supposed to be being said. So if there's too much deviation from a performer, frankly, it's not going to deliver that.

"But we are looking at merging this technology with speech recognition technologies so that future iterations of this allows for that variability in dialogue."

The smart glasses will now be rolled out for all of 2019's season at the National.