If the scratches are not too deep, you can polish them out by
a sequence of grindings with successively finer grits. This
is long and tedious, but is the technique used for preparing
surfaces for metallographic examination -- which is also used
for preparing glasses and ceramics for microscopic exam at
times.

Alternatively, one could attempt to fill in the scratchs
with something with the same dielectric constant vs. frequency
(i.e., same index of refraction vs. wavelength). Water-glass
comes to mind (sodium silicate solution in water) as a possibility.

I would try the water-glass first. If it is not good enough,
it can be removed with water-based solvents. If it is good
enough you can seal it with a clear coat of your choice.

For a CRT I would NOT recommend flame-polishing, which otherwise
would be my first choice for descratching glass.