What Causes A Warm Sensation In The Eye?

Hi,
Asking for my wife -she doesn't do computers. She has noticed a warm sensation on and off in her right eye. She said it feels like warm water washing over and behind her eye. It looks normal, pupils the same size, no change in vision. It happens with or without her contacts and started this morning as soon as she woke up. Seems to be increasing in frequency since yesterday.
Thanks