The more dots or pixels used on the screen, the greater is the clarity of the image. The monitor's refresh rate refers to how quickly the screen is redrawn. The faster refresh rate will result in less flickering and off course less eyestrain. You can check the flicker by looking at the monitor from left or right of the screen instead of straight ahead. The refresh rate decreases as the resolution or size of the monitor increases.
Monitors come in different sizes.
However, many larger monitors don't deliver image quality as high as a smaller monitor of the same price. Depending unpon the requirement you can choose the right one. Your monitor should be able to provide image sharpness and color balance, acceptable to your eyes. Generally, a large size monitor with lower dot-pitch numbers is better. These are flat screens with light weight and smaller footprint.