While there will always be variances that depend on the person, most hospitals and health providers recommend the top of the monitor to be at or below eye level.

“Place the computer monitor straight in front of you, directly behind your keyboard, about an arm's length away from your face. The monitor should be no closer to you than 20 inches (about 50 centimeters) and no further away than 40 inches (about 100 centimeters). The top of the screen should be at or slightly below eye level. If you wear bifocals, lower the monitor an additional 1 to 2 inches (about 2 to 5 centimeters) for more comfortable viewing.” Source: Mayo Clinic : Office Ergonomics - https://www.mayoclinic.org/healthy-lifestyle/adult-health/in-depth/office-ergonomics/art-20046169