"a squinting," 1680s, medical Latin,
from Greek strabismos,
from strabizein "to squint,"
from strabos "squinting, squint-eyed," related to strobos "a whirling round,"
from PIE root *streb(h)- "to wind, turn." Earlier in Englished form strabism (1650s).
The word "squint" has multiple meanings-- the ophthalmic definition being:
A condition of the eye consisting in noncoincidence of the optic axes; strabismus.
"Strabismus" does mean "squint", but squint doesn't necessarily mean "to look at something with your eyes partially closed".
In fact, in one of the historical examples on dictionary.com, the related word "asquint" is used in the following sentence from the 17th century:
But I know that Providence looketh not asquint, but looketh straight out, and through all men's darkness.
This usage seems to imply that strabismus (or at least not looking "straight out") has a long association with the word squint.