I have been learning about the function of tears and found that there are several layers that affect the lubrication of our eyes. There is an aqueous or water layer. But there are also a lipid, oil, layer that keeps the water from evaporating and a mucin layer that helps adhere the water to the eyes. We have melbomian gland under our lower lids that produce the oils. Not only does under production of tears from our lacrimal glands affect dry eyes but so does under production of oil when the melbomian glands are damaged or blocked.
My dry eye specialist did a special test, that I paid extra for, to look at the melbomian glands to see how healthy mine were.
(I noticed that a symptom of dry eye may be sensitivity to light!)
Some experts and those selling new dry eye treatments are saying/suggesting that overuse of saline tears may be affecting our own natural ability to lubricate our eyes. Definitely a cue to pause and reflect on the best way to support healthier eyes.
Here's an article that is selling a dry eye treatment process that I in no way endorse. But it does a great job of explaining how eye lubrication works.
Pilocarpine / Eyes
Dry eyes
Sjogrens 
