They have extremely far sighted vision. It is doubtful that they can make out a close branch as any thing other then a blur. It is normal. It is important to try to leave the cage like it is as best you can. Once they get settled into a cage for awhile they can navigate through it very gracefully.
A friend wrote an article that may be published someday. I didn't ask her where she got the data but knowing her, I'm sure that it was reliable...
Here's a quote:
"Comparatively, chameleons’ eyes produce the largest retinal image of any animal. Chameleons have evolved what has been described as a “mini-telephoto lens system” based on a myopic, divergent, lens, which creates a virtual image. Their eyes can focus as close as 3cm while the accommodation range is said to be up to 45 diopters and rapid, up to 60 diopters per second; similar to birds according to one expert."
If your chameleon continues to miss its target, there may be an tongue/eye-related health issue. Keep an eye on things .