Pascal Cotte said da Vinci built the painting up in layers, the last being a special glaze whose optical properties increased the illusion of a three-dimensional face.

Pascal Cotte said Leonardo built the painting up in layers, the last being a special glaze whose optical properties increased the illusion of a three-dimensional face.

After using the app 40 times, users with an average age of 51 were able to read two lines lower on an optical chart held 40cm from their face – a reduction in "eye age" from 50.5 to 41.9 years.