A drug that combats a debilitating eye disease could see mascara consigned to the dustbin after tests found it also doubles eyelash growth. So convincing are the side-effects of Glaucoma treatment Lumigan that its maker plans to apply for a cosmetic licence in the US.  It means sales in Britain could start as early as next year - allowing Allergan to compete for a share of the? 2billion spent on mascara each year worldwide. Interest in the cosmetic potential of Lumigan was sparked by the observation that the lashes of many patients being treated for glaucoma grew more quickly than expected. The effect was most obvious in those being treated in one eye, with the lashes becoming noticeably thicker, longer and darker. In a trial at Miami University, the drug, also known as bimatoprost, was mixed with a gel. Those taking part were given two gels, one containing bimatoprost and the other a dummy drug, and told to regularly apply one to each eye. The eyelashes treated with bimatoprost grew around 2mm in six weeks - twice as quickly as those coated with the dummy solution.  It is not clear how the drug lengthens lashes. In glaucoma, it works by lowering a build-up of pressure that can lead to blindness. More than 350,000 prescriptions are written every year in Britain. In the case of eyelashes, it is thought the drug's hormone-like formulation stimulates growth. If given the go-ahead for sale as a cosmetic, it could also benefit those who have lost their lashes because of alopecia and other conditions. Valerie Randall, professor of biomedical sciences at Bradford University, told the Independent on Sunday: 'What the company is doing now is amplifying the sideeffects of a medical treatment. When we understand better how it works, it could be used in the treatment of alopecia and other hair growth problems.'  Last night, Britain's Medicines and Healthcare Products Regulatory Agency urged people not to use Lumigan to lengthen lashes until its use as a cosmetic is deemed safe.                       - DM