An improved mechanism for extending and retracting a retainer strap for eyewear. The strap is disposed in a cartridge unit such as a box like container which may be inserted into the interior of one or both hollow temples of an eyeglass frame. Alternatively, the strap containing cartridge may be affixed to the exterior of the temple of any pair of eyewear of sufficient size to support the cartridge. Retainer straps suitable for use with the cartridge may be either elastic, inelastic, or one of each to provide for different modes of use.