Eye care professionals will sometimes dilate your pupils during an exam to get a better look at your retina. This simply means that your pupils will be widened (or dilated), usually using special dilating eyedrops.
The downside of getting your eyes dilated is that it makes your vision blurry and your eyes extra-sensitive to light for a few hours, or sometimes a bit longer. Sunglasses help a bit. (Safety tip: It’s not a good idea to drive for several hours after your dilation.)