Sometimes when capturing a photograph, the subjects eyes can be shadowed because there wasn't enough reflective surfaces bouncing light back to her or his face. Or, the image overall isn't exposed enough, making the eyes even darker.
The easiest fix for this, honestly, is in camera, by slowing down the shutter speed, or increasing the ISO, or opening up the aperture more. Also, using a reflector or something white in front of the subject will reflect light back onto her or him.
Once the image is taken, though, we have to do what we can to make it the best it can be. Below is an example of this, where the image is a bit underexposed and the eye area is quite shadowed.
The very first thing I did was bump up the overall exposure in the Basic panel to +.55, as well as moving the Shadows slider to the positive side, around +15. Changes made via any of the panels on the right-hand side of the Develop module are considered "global" changes because they effect the entire image, not just some of it. To make small, specific changes, you must adjustment brushes, graduated filters, radial filters, or the spot removal tool. After making my global changes, I click on the brush (below the histogram) and used some adjustments brushes.
Brighten Area Around the Eyes
The above image shows the brush settings I used to lighten her upper and lower lids. Doing this not only made her eye area lighter, it makes her seem more alert or awake. Sounds funny, but the same is said when a woman uses a lighter concealer below her eyes. So many Lightroom users will brighten the whites of the eyes and the pupil and iris, but forget about the area surrounding the eye. Usually I start with that, then move inward to the eye itself.
Remember Small Changes
As with all editing, less is more. It is incredibly easy to make the eyes looks so amazing and beautiful, but often that comes with a cost - they no longer look real or believable.
The next step I took was the brighten the iris and pupil of her eyes (above). While I was at it, I added in some sharpening to make them look crisp.
Below is a before/after comparison of edit. After brightening her eye area, I also smoothed her skin with the Smooth Skin brush from the Perfect Portrait brush collection.
Flow and Density
If you are attempting to use adjustment brushes in Lightroom, but you are experiencing trouble with seeing the effects you either need to increase the sliders, or you need to check your flow and/or density sliders. If they are low then you won't see the effects of your change.
Below is a screen shot showing where to click to open the brush menu (pink), where to click to access custom brushes (yellow), and where to look for the flow and density sliders (green). You can read more about flow and density by clicking over to a tutorial written specifically for them.
Custom Brushes from Pretty Presets
The screen shots I shared for this tutorial were of brush changes I used on this particular image. Normally I am not tweaking the brush sliders but rather using the custom brushes that come in the Perfect Portrait brush collection. This collection contains 40 brushes that can be used for portrait editing as well as still-life or landscape photography. The set includes 10 brushes that are specific to the eye area!
Eye Brushes (10)
Eye Color Blue
Eye Color Brown
Eye Color Green
Eyes Blue Shadow
Eyes Rose/Brown Shadow