Is it obligatory to inform the suitor about the daughter's hereditary disease, which may lead to future blindness, or is it permissible to conceal that, and what is the ruling on the marriage if it takes place without informing him?

The suitor does not have to be informed of every defect. Rather, he must be informed of defects that prevent intercourse, or are repulsive, or contagious. There is no need to inform him of a potential illness whose prognosis doctors might change. If the marriage is concluded fulfilling the conditions of validity, then it is a valid marriage.