 , only one such product had been approved for sale by the FDA, based on a technique for electrically pulling glucose through intact skin, and it was withdrawn after a short time owing to poor performance and occasional damage to the skin of users.Hundreds of millions of dollars have been invested in companies who have sought the solution to this long-standing problem.Approaches that have been tried include near infrared spectroscopy (measuring glucose through the skin using light of slightly longer wavelengths than the visible region), transdermal measurement (attempting to pull glucose through the skin using either chemicals, electricity or ultrasound), measuring the amount that polarized light is rotated by glucose in the front chamber of the eye (containing the aqueous humor), and many others.