Try to think of it this way:
Despite your best efforts, you are never going to be able to safeguard your child from every possible injury or hurt. And you know what? That's absolutely okay! Kids learn a lot from failing, from bumping into to the tables or walls, from using their toys, etc. While it can be sad that your child gets a bump or bruise, know that it isn't permanent and that the damage will not be lasting. On the bright side you're allowing him to discover and explore his world, learn about what works and what doesn't and then adapt/adjust what he's doing to work toward a positive or desired result...all on his own without you showing him the right way to do it!
Yes, the eye is red and bruised but after a few more times of hitting himself in the face with the rattle he will figure out that "ouch, this really hurts! Maybe I ought not do it again." Or, maybe the bump and bruise doesn't hurt him and he doesn't care.
Now, I'm not saying don't childproof and let your child be in danger but I am saying that infants, toddlers, and children get bumps and bruises even under the most careful and protected of situations. You can choose to be so overprotective that the child becomes afraid to do anything out of fear that they'll hurt themselves (not saying this is what you're doing, btw) or you can choose to allow your child to explore and learn from his mistakes in a safe environment.
For what it is worth, my 6 month old's knees are always red because he crawls everywhere. It looks unsightly, but it doesn't hurt him. Should I discourage him from crawling because it looks bad, denying him the opportunity to learn more about his surroundings, learn how to get a toy he wants, learn how to interact with his world? Of course not!