Look for changes in the upper neck if corrective lenses are used. Bifocals or progressive lenses often cause the head to look up for small font.
Lower the monitor 3-4 inches and review the head and neck position with a challenging target.
If a smaller font is needed, try increasing magnification from the computer operating system, or just move the monitor closer, to preserve spine posture.
Control glare by reducing lighting on the screen, or reducing light from behind the screen.
The secondary visual target may be paper.
Locate the paper in a position that is easier to see, and minimize the forward bend and rotation of the neck.
An alternative device like a tablet or smart-phone may also be needed, and that can be located with the paper using a slant board or copy holder in a place that does not require too much rotation of the neck.