@media (min--moz-device-pixel-ratio: 1.5),
       (-o-min-device-pixel-ratio: 3/2),
       (-webkit-min-device-pixel-ratio: 1.5),
       (min-device-pixel-ratio: 1.5),
       (min-resolution: 144dpi),
       (min-resolution: 1.5dppx) {
 
/* Retina rules! */
 
}

/*
Source: http://mir.aculo.us/2012/11/28/the-ultimate-target-retina-screens-media-query/
*/