There is a major problem occuring in the arguments about intelligent design, and that is the one that, roughly stated, says "If I were God, I wouldn't have done it like that!" This always makes me very grateful that the writer is not God. Our knowledge and understanding is so limited, that to presume to be able to decide what is good in the world of biological design and what is not 'good' is supreme egotism.
If, after all, we are the results of only natural forces, as evolution claims, then wouldn't that claim of a 'bad' eye for humans or a 'bad' back be a blow to evolution? If, after all, evolution is a result of natural selection, how on earth did such a bad eye or bad back or bad whatever get selected for? That decision that something is 'bad' is a two-edged sword for the evolutionist!
However, if we are considering intelligent design and/or creation, there are two items that must be considered:
1. We do not know enough to judge God, and
2. We do know that mutations, through time, can accumulate to produce significant damage in a population.
Thus, it is not intelligent design or creation which must answer to the judgment of 'poor design' in any human's analysis, but rather evolution which must somehow account for 'poor results.'
Personally, I find nothing wrong with the eye or the back. I don't like needing glasses, but accept that as a result of mutations plus heredity, knowing we were NOT designed with poor eyesight or an inherently bad eyeball design, but that the first is the result of time and mutations and the second only a judgment by fallible and ignorant human beings. As far as the bad back goes, I would venture to say that the vast majority of those who think it is a bad design have abused it rather than used it -- this can include the football player who is getting tackled for fun and profit as well as the computer geek who sits all day not using his back muscles at all.
All in all, the fact that we can still function so well while abusing ourselves in so many ways -- diet, sudden exercise or lack of it, stress, etc. etc., indicates that we were designed incredibly well. We have enough overlap of organ function to be able to be badly injured and still keep going. It is optimal to have everything functioning correctly, but as someone who was kicked in the gut by a horse many years ago, I can testify that one can live without a spleen and half a pancreas quite nicely. There are those who do well without a number of other bits and pieces of themselves as well. That's incredible design -- incredibly intelligent design.