The fundamentalist Christian group Answers in Genesis (AiG) preaches that evolution is wrong and everything was created directly by God. In this article they discuss why the eye must have been created. The argument essentially boils down to "If it wasn't built exactly the way it is, it wouldn't work at all". This suggests that the eye could never have arisen naturally. The article uses, as proof, the fact that the eye twitches constantly. This twitching (microsaccades) is imperceptible but has an important side-effect: twitching changes the light that appears on the cells of the retina and in essence refreshes the signal from those cells, so that your eyes can see constantly, even when nothing is moving. If there was no twitching, you'd stop seeing the image after a few moments, until something moved. This is because the retinal cells only respond to a change in light. Since the muscles that control this twitching are tiny, and the twitching is responsible for continuous vision, God must have made the twitchy muscles.
There are so many things wrong with this argument it's hard to know where to start. First, the argument is one of incredulity. Saying "It's absurd that such and such occurred naturally" is the same as saying "I can't imagine a way for such and such to occur", but some people have a better imagination than others. The fact that AiG don't understand how an eye might evolve microsaccades doesn't mean that those microsaccades didn't evolve.
The second problem with this argument is that it is quite obvious how microsaccades might have evolved. First, an eye evolves that doesn't have microsaccades. As the AiG article mentions, this eye can't see something if it isn't moving. However an animal can be born with a mutation where this animal's eyes are naturally twitchier. As a consequence, this animal sees better than his brethren and is a better hunter (or is better at escaping hunters), and thus has a better chance of surviving. Animals that survive longer have more offspring, thus propagating the mutation. This is only one possible scenario; in order to account for the tiny twitching muscles in the human eye it's probably required that the twitching evolved at the same time as the eye. Twitching is often a defect, but as a computer programmer I can assure you that defects often become features.
The third problem with this argument is that it denies God's own perfection. This isn't a problem for evolution, but a strange paradox in the creationists' arguments. If God is perfect, and he designed the eye to perfection, why did he make it so that it has to twitch in the first place? It doesn't make sense. If you're designing an eye, you don't make a photo-receptor that only works when the light changes, and then fix that by constantly changing the light with twitchy muscles. Rube Goldberg would have come up with a better system. And don't get me started on the testicles being outside the body.