Dani Diamond of Fstoppers recently shared a pretty quick and clever way to removing those dark patches you have under the eyes of your subjects.
Ignoring the commonly used patch tool, Dodge/Burn tool and Clone tool which either copy the texture as well as the color or smudging the texture altogether. Instead, Dani opts to use the curves tool which allows improving the dark tones while not affecting the texture. The entire tutorial and more examples can be found at Fstoppers.
P.S. If you are looking for a more complete/glamor eye retouching check out this tutorial from Dave Piper.