Paul:
Yes, like a TV set, most CRT monitors have a screen control on
the high-voltage (flyback) transformer. The one with the big red
wire going to the top of the picture tube.
The screen control is the lower control. 17" and larger monitors
have 2 focus controls and 1 screen control. Smaller monitors have
just 1 focus control.
Note: some monitors do not have screen controls and you have to
manually change a resistor in the screen circuit to control
the brightness.
John