This reminds me of an argument I posted on here a while back (not sure about original pic):
Daily reminder that 90% of atheists are retarded, underage b& newfags Anonymous
Aside from the fact that the "inverted" retina allows the eye to process the higher amount of oxygen it needs in vertebrates, or that it's practically impossible even to conceive of how it might be modified without significantly decreasing its function, or that atheists have such trouble even finding a bodily system to quibble about in the first place despite there being a centillion number of systems in the human body, let's look at this anyway:
Perhaps you've seen this argument; pic related.
It's basically something like
>hurrr if God exists how come there are blind spots checkmate Christians XD
Questions aren't arguments, so this is already invalid, but here's the argument made explicit:
>1. If God were to exist, eyes wouldn't have blind spots.
>2. Eyes do have blind spots.
>3. Therefore, God doesn't exist.
Begs the question
Now here it is with all its implicit premises made explicit:
>1. There are designs for the human eye that would allow us to see better.*
Begs the question
>2. It is possible to see better.
>3. God's purpose for eyes would be for us to see better.
Begs the question
>4. If God were to exist, He would have designed the eye so that we see better.* (from 2 and 3)
>5. Human eyes have blind spots.
>6. We don't have eyes that allow us to see better. (from 5)
Non sequitur. Implies a false equivocation between "blind spot," colloquial understanding of "blind spot," and not seeing better
>7. Therefore God doesn't exist.
*"Better" can be defined as "as clearly as possible," "as much as possible," "more," or any arbitrary word or phrase you want.
Remember kids, pointing out these fallacies isn't bitching about minor technicalities, but showing the argument to be unsound and stupid.