QUOTE ("RC p108 Reduced Sense")
For 10 BP, the chosen sense is completely reduced and
the character suffers a –6 modifier to all Tests towards which the
sense might contribute.
Further Down
QUOTE
Blind/Reduced Sight: A character with Fully
Reduced Sight is legally blind and receives a –6 dice pool modifier
for all vision-based Tests. Note that since their astral perception is
not a visual sense, Awakened characters with the Blind quality may
still perceive astrally, though gamemasters are advised to strictly
apply the Astral Visibility modifiers on p. 114 of Street Magic.
A ghoul gets this Weakness, RC specifically states the -6 modifier.
And it is the "rule" for modifiers for reduced senses.
As you said, the eyes of a ghoul are broken. So he gets a negative dice pool modifier whenever he tries to perceive something visual.
But they can use astral perception to make up for it, like identifing people, recognizing objects, maybe even communication (more in the like of body language, but i wondered, if ghouls actually use the emotions they "read" from their family).
But it isn't a visual perception, astral sight is a psychological sense, more like "feeling" around. You don't have literally eyes in the astral space nor ears, yet you can see and hear in astral, even feel, propably even smelling and tasting.
Now, my Fun-Question was just fooling around, but your question could be answered easily (at least with my view of the whole astral perceiving thing): Yes he can. It's called Switching off Astral Perception

Happy new Year by the way