Answer:
He means that these people have impaired eye functioning
Step-by-step explanation:
The word "handicapped" refers to a malfunction of some body structure, allowing a person to become deficient in something.
When Mahoney states that "those who can see are handicapped" he means that the functioning of these people's eyes is not efficient or that their eyes do not work at all, so much so that they cannot see something clear and evident.