Hi, I find the easiest way to put gel/cream in cat's eyes is to squeeze a small amount out of the tube and onto my thumb, then facing the cat just hold it's face (with it looking at you) and quickly swipe your thumb across their eye. They are usually a lot more trusting of your thumb coming towards their face than a mean scary tube. Plus you'll probably be more confident that you're not going to hurt the cat by sticking the tube in it's eyeball (especially if it's the little metal tube type!).

Oh, and your aim is to get as much in the eye as possible, rather than just around the rim