Beauty may be in the eye of the beholder, but the secret of what constitutes an attractive face could actually lie in a mathematical formula originally devised by artists like Leonardo da Vinci.

Scientists at the University of Nebraska say they have developed software that can predict whether or not a face will be deemed beautiful, using a calculation that calibrates the symmetry and geometry of the face.

Amazingly, the boffins' beauty results are practically identical to a code that da Vinci and the Old Masters followed to paint perfect beauty back in the 15th century.

The Renaissance artists used six Neo-Classical criteria as a guide to defining a beautiful face, among them being that the width of the face must be four times the width of the nose. In addition, the code stipulated that the height of the forehead, length of the nose and the height of the lower face must all be of equal length.

Last week, biostatisticians confirmed that out of the six Renaissance beauty rules used in their computer programme, only one turned out to be wrong. That was the so-called 'divine proportion' or 'golden ratio' between mouth and nose width (the artists said the ratio should be 1.5, whereas the scientists found it to be 1.618).

The rules were then tested on 36 volunteers who responded strongly to those 'ideal' Renaissance traits in pictures of celebrities like Meg Ryan, Rock Hudson and Keanu Reeves. To add to the theory, a recent documentary on Kate Moss argued that her features have the golden ratio of 1.618, which could explain her phenomenal popularity as a model.

So, just how has the Renaissance formula stood the test of time? It could be because the criteria incorporate the basic psychological triggers that alert the mind to beauty -- and ultimately to sexual reproduction.

"Facial symmetry is probably the most important factor in determining what we consider attractive," Philip Malone, a psychoanalyst and Head of Psychotherapy at the Independent Colleges in Dublin, explains. "Generally, research shows that people will select faces that are more symmetrical as being the most attractive.

"Faces that are consistently rated as attractive normally have the size of their features in proportion. It's believed that such factors reflect good genes, and therefore make that person a better candidate for the production of healthy offspring.

"One of the main areas of the brain thought to be important in the designation of attractiveness is the orbitofrontal cortex, parts of which seem particularly active when judgements of attractiveness are being made.

"This system seems to be important in so-called 'social reward' processing, which assists us in making judgements regarding the value of potential mates."

However, irrespective of the Renaissance formula's endurance, the most cursory glance through history shows that perceptions of beauty have constantly evolved according to social and cultural trends.

In his classic tome On Beauty, Umberto Eco tells how Greek philosophers first put forward the idea that beauty lay in proportional and symmetrical features, while later in the Middle Ages, a pale complexion was deemed the height of beauty (to the extent that women used to slap white lead on their faces and even make themselves bleed to achieve the look).

In modern times, notions of what is deemed beautiful have also been turned on their heads time and again, and these changes can be viewed through the prism of the modelling industry, that great litmus test of what's popularly -- or, at least, commercially -- deemed beautiful at any given time.

"If you look at the 1930s and '40s, the great beauties were Hollywood stars like Ava Gardner and all those magnificent, glamorous, curvy women," explains Limerick-based model scout Celia Holman Lee.

"Then in the 1960s, it was all about the boyish, Twiggy look, followed then by Cheryl Tiegs, Christie Brinkley, and then the reign of the supermodels like Cindy Crawford and Elle Macpherson.

"To my mind, the supermodel period was the most interesting in terms of what was considered beautiful, because there was such a variety. There wasn't a set look like the Twiggy era. The supermodels were there in their glamour and their beauty, and they all looked totally individual.

"Right now, the concept of beauty in the industry has gone from all the great supermodels back to the gaunt, quirky look of someone like Agyness Deyn. She is beautiful in a particular way; not the divine way of Crawford and Claudia Schiffer.

"That quirky look applies to men too. Once upon a time, male models had to have a strong, masculine jawline. Today, they look softer and a lot more feminine."

But before your own self-esteem bottoms out and you grab a ruler to gauge the ratio of your facial features, the scientists involved in last week's beauty breakthrough stressed that their results "can be extended in many different directions, and that attractiveness is complex and involves many other issues".

In Holman Lee's mind, the test of an enduring beauty isn't the golden ratio, but rather simply the eyes.

As she says: "Look at Twiggy. She was an icon in her day, but when I look in her eyes, I can still see the Twiggy I idolised in the '60s. It's the eyes that hold the power to entrance."

Beauty around the globe

> In India, it's commonly held that the fairer a person is, the more beautiful they are. Many Bollywood stars, such as Aishwarya Rai, are chosen for their fair skin, and the fact that they have eyes that are blue, green, grey or light brown.

> In parts of Asia -- mainly Japan and China -- the double eyelid is considered more beautiful than the single one. Hence, many opt for surgery to 'correct' this. Also among the Straits Chinese, a perfectly egg-shaped face with high forehead and bright eyes are regarded as more desirable in women.

> In the Middle East, blue and green eyes are considered the most beautiful, which makes contact lenses in those colours extremely popular in the region.

- Declan Cashin