BBC News disability affairs reporter
Visually impaired people are now increasingly able to join in the video gaming fun thanks to an ever-expanding range of audio games.
They even have the potential to turn into new gaming genres in their own right which could start to appeal to sighted gamers.
More games are being made which do not rely on sight
But, compared with the millions of copies of PC and console games sold every year, the market for audio games is still relatively tiny.
"My guess is that about 3,000 audio or blind-accessible games are sold a year," said Richard van Tol who jointly runs Audio Games.Net, an information site for fans and developers.
"Loads of blind people have computers but not many of them know about audio games."
There are currently about 50 commercially available titles on the market, with perhaps three times as many freeware and shareware options.
Like their graphics-based cousins, the games come in many varieties - adventure, arcade and so on.
But certain elements are essential according to Canadian Kelly Sapergia, who regularly reviews audio games for ACB Radio - a dedicated service for blind listeners.
"They need to have really distinctive sounds so that you can easily tell where you are," he said.
KELLY'S TOP FIVE GAMES
1 - GMA Tank Commander
2 - Aliens in the Outback - invaders with an Australian twang
3 - Dark Destroyer - another invaders game
4 - Lock Picks by L Works - you become an expert safe cracker
5 - Golf by Jim Kitchen
"This can be achieved using different ambient music and having the footsteps change depending on whether you're on grass or mud."
Mr Sapergia also thinks that good dialogue is necessary to guide players through the game.
"First and foremost, it must be fun," said Richard van Tol. "Secondly, it must be understandable because you don't have any visual references."
And both agree that good games need sufficient elements of competition and have to be attractive enough to make players come back for more.
Out the box
One of the first commercial companies in the marketplace was Bavisoft, a small US-based developer which has two titles to its credit and a third due for release in 2005.
"The idea for creating audio games came from our president, Jeff Gibbons, who is colour-blind," said Bavisoft sales and marketing director Russ Byer.
Mr Gibbons had always experienced problems playing video games because of the lack of proper contrast. For him certain things were completely invisible.
"As he's a musician, he had the idea of making a game just based on sound and the idea grew from there," said Mr Byer.
Bavisoft says its main focus is not on people being unable to see, but more on what would be a fun thing to do.
"If it's impossible to make the activity audio-based, we have to re-think the idea or think outside the box," said Mr Byer.
The company's second title, Chillingham, is an adventure set in a haunted village.
Players have to solve puzzles and, on the way, need to defend themselves from attacks by vampires, witches and werewolves.
Fending them off requires either excellent stereo speakers or a good pair of headphones in order to locate them in the stereo picture.
Games on the move
Mr Byer said that he and Mr Gibbons had grown up playing text adventure games but they also loved the arcade variety.
"Our games have the feel of the old text adventures but then, at times, there will be action sequences which are like mini arcade games," he said.
"The result is hopefully more than just a text adventure made for sound."
Games for visually-impaired could have a future on handhelds
The games have developed to such an extent that some people are predicting they could soon be popular among sighted players.
But Richard van Tol thinks platforms like PCs and games consoles are so inherently graphics-orientated that sound-only games are unlikely to break through.
On the other hand, small, handheld devices - mobile phones, PDAs and the latest portable games devices - could be ideal for furthering the audio game genre.
"Maybe people will use them on the move a bit like personal music players," said Mr van Tol.
He thinks another limiting factor is the lack of good quality audio engines.
"The current 3D engines only use the X-Y axis. The sound's either in front of you or behind, there's no above or below."
While it may be some time before the majority of gamers talk of developing good "hand-ear co-ordination", visually impaired people can now look forward to a brighter gaming future.