To Apply Adjustments Selectively (to a part of the image)
1 Create a Levels adjustment layer and choose Levels to brighten or darken image, Hue/Saturation to adjust color, or other adjustment. Make adjustments looking on a specific area (not at the whole image - e.g. eyes only), and click OK.
2 Fill the layer mask with black to conceal the adjustment. 
Use Paint Bucket Tool or Edit > Fill...
3 Paint with white at 50% opacity again, this time to brighten the eyes only.
To overdo it, you can switch colors and paint with black, or simply lower the opacity of the adjustments layer in the Layers palette.

 

Selective Sharpening
1 In many projects it is preferable just to sharpen the selected areas, like the eyes and mouth, rather than sharpening the entire image.
  • First, create a new stamp visible layer
    (Ctrl, Shift and Alt keys, then type N and E).
  • Set the blend mode of the layer Overlay.
  • In the main menu go to Filter > Other > High Pass. Set the radius (1.5 pixels) and click OK.

At this stage the sharpening effect is global.
2 We can limit the sharpening effect to specific areas by painting directly onto the High Pass layer with a 50% gray color.

Click on the foreground color in the Tools palette. Set the HSB values to 0,0 and 50 respectively. With 50% gray as your foreground color you can now paint the smooth areas of skin to ensure they are not sharpened.