Ophthalmologist Craig Blackwell described the 'Dry Eye Cycle' in two excellent videos with graphic descriptions. From his description it becomes clear that the Dry Eye Cycle really consist of two self-reinforcing feedback loops. I have constructed these feedback loops here because they help explain the cycle, and understanding it may be very useful for suffers of the often debilitating 'dry eye syndrome '. The process usually starts with one of two deficiencies: the oil secreted from oil glands is too thick and does not adequately cover the aqueous film leading to evaporation and dryness or tear glands do not produce enough tears.  Dr. Blackwell stresses the role of inflammation which can lead to the progressive worsening of the condition and  which should be controlled. He suggests various treatments. I highly recommend watching the videos

https://www.youtube.com/watch?v=ooYcjzNtn58

https://www.youtube.com/watch?v=TwpWKCM31JI