The photo below shows what may be a CRT for the TX-0 (transistorized experimental computer) in 1956, referring to what may be a CRT on the left side, not to the CRT on the right side .
If that is a CRT on the left side, what is it displaying ?
The image is sourced from the following webpage, just click 2 times on the tiny image of the TX-0 on the timeline on that webpage to expand it to it's maximum size - history-of-computers-timeline
The image below the TX-0 image, shows that a crt screen with square looking corners ? ( not sure though ) did exist in a similar time-frame, it shows the DAC-1 possibly in 1959 .