Lakette I don't have experience of visually impaired babies as such but I do have a lot of experience of the visually impaired because i have been blind since birth.
There is no evidence to suggest that VI children develop at any different rate to sighted ones, but sometimes development needs to be assisted in different ways than with a sighted child. A baby will often lift its head up because it wants to look at something, or crawl because it wants to get to something, if the visual stimulation isn't there, then that needs to be replaced by an audible one. Try and hold a mirror near to your baby's face and see if she responds at all, try doing this without making any noise so as not to alert your baby to what you are doing. if she does not respond then rattle a bunch of keys close to her and see how she responds to that, not too loudly of course if she is hypersensative to noise.
The reason why your DD seems to be in a world of her own and jumps if someone touches her may purely be because she can't see them, if someone walks up behind you and touches you when you're not expecting it, it would give you a fright, for your DD this may be exactly the same, she doesn't know where you are and so when you touch her unexpectedly it will frighten her. As she gets older she will learn to deal with this in different ways, perception is a great thing, but in the meantime it might be a good idea to talk to your DD constantly, especially when approaching her, that way she will at least know you're near her and won't get a fright when you touch her.
Sometimes diagnosing visual impairment is difficult, especially if a child has some vision, even light perception. I have light perception and would turn my head to the window when placed near it, would look at white objects because the light reflects on them, but I have no further vision, but as a result it was 3 months before I was diagnosed as being blind.
This will not be the end of your world, if visual impairment is all your DD has, then she will go on to lead a normal and fulfilled life. Don't treat her any differently, let her do the things she wants to do, (I rode a bike and had rollerscates etc when I was a child), she will thank you for allowing her to be independent.
I am 32 now (well will be on Friday) I am married, I am a SAHM and have a 3 year old DS and am TTC for baby no 2, before having a baby I worked as a finance manager, before that as a customer adviser, and also as a secretary. I am totally independent and there is nothing I cannot do, (well apart from drive a car but that's not the end of the world).
If you need any advice, and I don't profess to know averything but I will always try to help, then feel free to cat me or email me at [email protected]
sorry for long reply, good luck