Intrigue is usually focused on her enigmatic smile.

But the Mona Lisa was at the centre of a new mystery yesterday after art detectives took a fresh look at the masterpiece – and noticed something in her eyes.

Hidden in the dark paint of her pupils are tiny letters and numbers, placed there by the artist Leonardo da Vinci and revealed only now thanks to high-­magnification techniques.

Under the microscope: Historians in Italy have discovered that by magnifying the eyes of the Mona Lisa painting tiny numbers and letters can be seen

Hidden symbols: This eye is thought to contain L and V, the artist's initials

Experts say the barely distinguishable letters and numbers represent something of a real-life Da Vinci code.

The revelation could have come straight from the pages of Dan Brown’s best-seller The Da Vinci Code, in which the Mona Lisa is said to contain hidden clues about the Holy Grail.

Silvano Vinceti, president of Italy’s National Committee for Cultural Heritage, which spotted the symbols, said: ‘To the naked eye the symbols are not visible but with a magnifying glass they can clearly be seen.

Genius: Historians believe that Da Vinci's love of riddles led him to paint himself as a woman - with some believing the Mona Lisa is a self-portrait

‘In the right eye appear to be the letters LV which could well stand for his name, Leonardo da Vinci, while in the left eye there are also symbols but they are not as defined.

‘It is very difficult to make them out clearly but they appear to be the letters CE, or it could be the letter B.

‘In the arch of the bridge in the background the number 72 can be seen or it could be an L and the number 2.

‘You have to remember the ­picture is almost 500 years old so it is not as sharp and clear as when first painted.

‘From the preliminary investigations we have carried out we are confident they are not a mistake and were put there by the artist.’

Mystery: The codes and riddles that the artist hid in his work were illustrated in the Dan Brown book and 2006 film 'The Da Vinci Code'

The search was initiated by another Dan Brown-style plot device after a fellow committee member discovered a musty book in an antique shop ­referring to symbols in the Mona Lisa’s eyes.

Mr Vinceti added: ‘Da Vinci put a special emphasis on the Mona Lisa and we know that in the last years of his life he took the painting with him everywhere.

'We also know that da Vinci was very esoteric and used symbols in his work to give out messages.

‘Who knows, they may even ­possibly be a love message to the ­figure in the painting.’

Mr Vinceti is a member of a group which is seeking permission to exhume da Vinci’s remains from his tomb at Amboise Castle in France’s Loire Valley.

They want to see if the artist’s skull is there so that they can try and recreate his face and establish if the Mona Lisa – owned by the French government and on display in The Louvre – is in fact a twist on a self-portrait of the artist as some believe.