There are three reasons why some seniors don't want others to know they have vision loss. The first is a tremendous fear of blindness, coupled with the belief that acknowledging
any vision loss is the first step on the way to blindness. They also often think that others will assume they're going blind if they say they're having vision problems. Most seniors with vision loss have macular degeneration, which doesn't lead to blindness. If that's the case with your parent, you should make that fact very clear.
Second, they don't want to feel "different." Approximately 30 percent of seniors in the United States who are 80 or over have some level of macular degeneration, so that in any assisted living residence many people are dealing with a similar experience. How about talking to the staff at your father's facility and see whether they can arrange a macular degeneration support group and posting a notice about it so everyone will realize how many of their neighbors also have some vision loss?
And finally, the emotional threat of vision loss comes from the enormous fear of losing independence, so empowering your parent to remain as independent as possible will likely reduce the impact of his vision loss and allow him to feel more like himself again. You can do that by putting him in touch with resources like low-vision rehabilitation centers, which teach people how to deal with impaired vision, finding devices (like reading machines or cooking aids) that might be useful, and training him to use those devices, if necessary. When he feels as if he has a handle on his vision loss, he may be more willing to acknowledge it to others.