The centre of the target is not much bigger than, let us say, your average grapefruit. So with a bow and arrow from 70m away there's very little room for error.

And although Im Dong-Hyun can barely read the big letters at the top of an optician's chart, he can hit that small, yellow circle time and time again.

In fact he holds the world record for the highest score from 72 arrows.

I caught up with him in practice at South Korea's National Sports Training Centre in Seoul.

The 25-year-old had to check occasionally with his better-sighted team-mates, practicing on either side, to find out whether his arrow had found its mark.

Many more times than not, of course, it had. In tests of his vision Im Dong-Hyun scores 20/100 and 20/200 in his right and left eyes respectively.

IM DONG-HYUN - THE FACTS Home town: Seoul, South Korea

Born: 1986

Discipline: Recurve archery

Career highlights: 2007 World Champion, member of two time Olympic gold medallist team and member of three time World Champion team

He laughs at the suggestion made in some media reports that this makes him "legally blind". But it is certainly poor eyesight, and enough, one might think, to rule out winning an Olympic gold medal in archery.

He now has two of those to his name, as well as four world championship golds to boot. "With my vision, when I look at the target, it looks as if different colour paints have been dropped in water," he tells me.

"The boundaries are not that clear and the lines between the colours are very blurred."

But Im Dong-Hyun simply aims at the ill-defined yellow blob, shimmering and fuzzy at 70m, and somehow his poise, strength and technique combine to put the arrow right on target.

He could, of course, improve his sight with glasses or contact lenses, but chooses not to. He has simply become accustomed to seeing the target this way.

His sporting career began more than 10 years ago, at his primary school in the city of Cheongju, 100km south of Seoul.

A teacher suggested that he try archery and the rest would be history, as they say, except for the fact that one major achievement still eludes him - the men's individual Olympic gold.

Despite the strength of the sport in South Korea, its archers have never managed to get their hands on the men's individual Olympic prize.

The gold medals that Im Dong-Hyun has won so far are team golds, which South Korea claimed at Athens in 2004 and Beijing in 2008.

Often the favourites - as he certainly was in Beijing - it seems as if the huge expectations placed on South Korean archers have simply proved too much.

"There's a huge amount of pressure," he tells me.

But looking ahead to the 2012 Games, this confounder of opticians everywhere appears relaxed and quietly assured.

He will arrive in London with even more experience under his belt and, with two more years of careful preparation, he believes that the ultimate prize is now within his reach.