What role did technological advances play in propelling american migration all the way to the pacific ocean

It helped bind the growing country together.

True blindness may be caused by trauma to the eye, severe conjunctivitis due to  ibr (infectious bovine rhinoceros) or pink eye or other infections, leptospirosis, lead poisoning, selenium toxicity, fungal infections, vitamin a  deficiencies, rabies, vitamin b12 deficiency, neoplastic of the orbit or  conjunctiva, cataracts, congenital malformations, etc.