This is a problem for many of us who wear glasses and whose eyes are unable to focus at different distances readily. Such conditions as might cause that are being over 40 and having presbyopia. or "old-age far-sightedness." There are other conditions that cause the lens to lose flexibility, too.
Most, but not all, cameras these days have a relative viewing distance of about 1 meter. Having your glasses or contacts set to focus at 1 meter usually solves the problem, but induces others.
You can also get corrective lenses for your camera's viewing system and some cameras even have adjustable correction built in. The add-on kinds are called "diopters." They are available on-line and most large camera stores. The problem is figuring out what correction to buy, so go to a big camera store and try them until you find your proper value.