Fascinating reading the comments to see some people say it works flawlessly and others say it's terrible and jittery. I'm wondering if it's lighting conditions

Fascinating reading the comments to see some people say it works flawlessly and others say it's terrible and jittery. I'm wondering if it's lighting conditions? Bright light will allow the phone to read your eye position far more accurately than the noisy pixels in a dark room. Or did Apple do a big upgrade to their front camera recently that accounts for the difference?