Round eyes are those that are open and are widest in the middle.
This guide will show you how to complement them, and elongate if you prefer...
They're mostly comparable to a baby's eye.
You can tell them apart mostly because of the dip they have on the bottom lash line.
A great example is Katy Perry.
The roundness is often even more pronounced than hers with a more drastic curve on that lash line.
There are two effects you can create with your brows. To emphasize the roundness of your eye, you can have a higher arch, and brows that become thinner at the ends.
To make them less round, you have a straighter arch and an almost uniform thickness.
Here's an example...
Same eyes, different eyebrows. The frame affects the way the eye shape looks within it...
This eye makeup complements the roundness of your eye. You're keeping them open, and just making them a little more striking.
The best way to do this is to keep your colors neutral, and focus on the eyeliner.
If you want to add color, here's how
Since your eyes are already round, elongating them means skewing the round shape. So you will use eyeshadow and/or liner strategically to make them a little flatter.
Use a horizontal pattern on the lid, and use eyeliner only on the top lid. When lining your eyes, first do the waterline. This will thicken those lashes and bring the lid down a little. It'll make it look a little heavier.
Then line the lash line. Make the eyeliner as thick as you'd like,as long as it's even across the lid. If your lids are already heavy, you may want to give it a little bit of a brushing to blend it and make it softer.
You can even wing it out for a little more linearity.
If you want to use eyeliner on the bottom lid, use a brown one that won't emphasize that bottom lash line.
If it's dark, it will define the bottom lash line and complete the circle. This will make take your eye back to looking round. So rather use a light eye liner, and fade it out into a soft shadow for even less definition.
Often, round eyes are also prominent, so you might want to check that out and combine the advice...Makeup Know How > Eye Shapes > Round Eyes