Visual impairment and guide dogs?

im just curious how is the process of applying, like is there a criteria? I'm registered as blind (have been since the age of 2/3) however I do have vision I can use. I use a cane currently however sometimes I feel it's still not the best tool, I struggle with crossing roads (with no crossing) and I have no peripheral vision (I have nystagmus.) are there are advantages to using a dog as an aid over a cane, do you use both? I'm 20 and currently at university, I've not mentioned it before, and nobody has suggested it, and I'm not sure if it would be better for me or not?