I have a 7-year-old 15" CRT monitor that is connected to a standard PC.
Lately I noticed that the size of the monitor's onscreen image is
affected by changes to the image's brightness (the brighter the wider).

For example, my Desktop background is dark. If I click to maximize a
white window, the onscreen image expands by (approximately) 1mm on
every border. If I then click to minimize the window, restoring the
dark Desktop, the image contracts to its previous state. The same
occurs when the monitor's Contrast control is quickly rotated from one
end to the other.

Is this behavior normal or a sign of a dirty or aged CRT? And speaking
old CRTs, would it be wise, with respect to health or sight risks, to
continue to use this monitor as long as it's operating properly (as the
average user would say)?

Dave