Compounds designed to treat aesthetic conditions have been a boon to some drugmakers in recent years, particularly for Botox and silicone-breast-implant developer Allergan (NYSE:AGN). In conjunction with its annual research and development day yesterday, Allergan discussed its next attempt to supercharge the medical aesthetics market: a new drug to help grow longer eyelashes.

This use for a compound called bimpatoprost came about by accident, according to Allergan. Even though the company is best known for its beauty-related products, it derives its largest portion of sales from its portfolio of eye-care and ophthalmology treatments, including dry-eye treatment Restasis. Over time, Allergan noticed that patients taking another one of its eyedrop treatments, Lumigan, were experiencing noticeable eyelash growth.

There are no prescription compounds approved for eyelash enhancement, and mascara from cosmetics companies like Revlon (NYSE:REV) and Estee Lauder (NYSE:EL) represents a global $3.7 billion market, according to Allergan. The company decided to capitalize on this opportunity by formulating bimatoprost, which contains the active ingredient in Lumigan, but is applied to the eyelash instead of in the eye.

Bimatoprost still has to get through the FDA rigmarole before Allergan can start marketing it. Not surprisingly, the FDA takes a much harder stance when reviewing prescription drugs used for cosmetic purposes than it does for other drug candidates.

If Allergan sticks to its guidance and files a bimatoprost marketing application in Q3 2008, the FDA will likely make its approval decision on the drug in mid-2010. Provided the drug can clear regulatory hurdles, Allergan estimates that bimatoprost could eventually bring in global peak sales of more than $500 million a year.

Allergan has guided for sales of at least $4.4 billion in 2008. While it will take some years for bimatoprost to reach Allergan's peak sales goal for the drug, merely meeting these sales estimates will still make it a significant growth driver for Allergan's top line. Any investor would bat an eyelash at prospects like that.