On the Pro tab > Pro Adjust effect, try increasing the Clarity and Sharpness. This will affect your entire image, but if you turn on Effect Painting (by clicking the button towards the end of the effect) and tick the Reverse effect checkbox (at the bottom of the “Effect Painting” dialog), you can then just paint on the areas where you want the sharpening to occur.
Other relevant effects which you may or may not be familiar with would be the Retouch tab > Eye Bright and Eye Color effects.
Let us know if you have any other questions!
Regards – The Ribbet Team