First of all, before the experts start attacking me with technicalities I’d better explain that there are two kinds of tears: constant tears, which are complicated, and reflex tears, which are simpler. As luck would have it we really are only concerned with the complicated ones today. After all if it was that simple, you’d be out enjoying the sunshine rather than reading about dry eye treatments.

(Okay, okay, to save you the trouble of looking them up in the encyclopedia: constant tears are the kind your eyes are constantly producing without your being aware of it and which keep your eye (well, maybe not YOURS but most people’s) reasonably well coated throughout the day and night. They are complex. Reflex tears, on the other hand, are simpler, and they are the ones that make your makeup run when you’re crying, or that make your eyes smart when you’re running on a windy day, or that try to wash grit out of your eye by themselves. As luck would have it, it’s the complex ones that we have to deal with.)

Now, back to those constant tears. There are four basic components you should know about: oily stuff, watery stuff, sticky stuff, and other stuff.

Oily stuff (lipids)

Remember in your science lessons about 20 years ago where you learned that oil floats in water? Well, guess what, that’s true here too! The lipid layer is oily stuff that sits on top of your tears. It is made by your meibomian glands, glands sitting in both your lower eyelid and upper eyelid margins. The purpose of the lipids is that they keep the watery part of your tears from evaporating. If you think about it, that’s a good thing. Suppose you’ve got lots of tears, but no lipids, well, your tears will evaporate and your eyes get dry. Fine, your eyes will (well, for most of you anyway) just keep making more tears, but what happens if your tears are evaporating faster than you can make new ones? Big problem. That is the problem, or rather one of the problems, that a lot of us have. In fact, if you don’t seem to have a problem with the watery stuff but still have "dry eye", this is almost certainly a big part of your problem.

The main reason you might not have enough oily stuff (lipids) is simply that those meibomian glands, the things that make it, get clogged. The oil is supposed to be nice and warm and runny, but sometimes it can get thick and gets stuck. This is fixable. Lid therapy helps deal with this by first kind of melting the stuff that’s thickened up, then gently squeezing it out. A drug called doxycycline is supposed to help too. Some nutritional supplements may be useful as well.

Watery stuff (aqueous)

This is the main part of your tears. It’s secreted by the lacrimal glands, which are in your upper eyelids. You either make enough, or you don’t. If you don’t, this is a problem. This is probably the closest thing to true "dry eye" that there is. If you don’t have enough tears of your own, usually you’ll be told to add some fake tears (artificial tears) or, if you’re so dry that you’re adding tears all day long, you’ll probably be given tiny little plastic plugs in the little holes your tears drain out through, so that you can trap the tears you have in your eyes as long as possible. If those work really well, some people burn the holes shut so they don’t have to worry about the plugs falling out. And if that’s not enough, well, first you need to make sure you haven’t got any of the Other Problems or that if you have, you’re treating them. And if that’s not enough, there’s some, ahem, sort of experimental treatments and drugs you might want to look into. They’re anything from drugs to... tarrsoraphy, where they sew your eyelids partway shut. Mind you, we don’t know ANYONE who has actually done that, not even after LASIK, not even the worst cases we know, so don’t start worrying about it.

Now, if you don’t have enough of this watery stuff, AND you don’t have enough lipids to help you keep the small amount of watery stuff your lacrimal glands can be persuaded to actually produce from evaporating as fast as it’s made, then you’ve got an Even Bigger Problem, and you need to address both problems separately.

Sticky stuff (mucins)

This is Rocket Science, we are told. Really high-tech spooky stuff that no one actually understands. — Just my luck, you say. The very thing that’s probably wrong with me, they don’t even know how it works or what to do about it when it doesn’t work. Yes, our feelings exactly — sigh.

Anyway, the point of the mucin layer is to make your eyes wet. "Hmm," you will say. "But if I have tears in my eyes, doesn’t that, well, by definition, sort of mean that they are wet?" Sorry, no. This just isn’t your day, is it? Look at your car when it’s raining. Could you swear that the entire surface is wet? Look carefully. No? See, I’m no scientist, but I kind of figure that unless you’ve got it totally submerged in water (and please don’t try this experiment with your car) a lot of things don’t actually stay 100% wet across their entire surface for very long. — Porous things that soak up water, fine, but smooth things, well, that’s a little harder. So it really DOES take a special kind of substance to stretch and spread around and stick to your eye. Hence Rocket Science. And the watery stuff (aqueous) sits on top of the sticky stuff (mucin). Where mucin goes aqueous will follow. Where mucin doesn’t go, well, that’s going to be dry. And unprotected, because that’s the other job of the mucins, standing between your corneas and the big bad world of bacteria.

Like I said, mucins are Rocket Science, but we’ve been told they’re made by something called Goblet Cells and that surgery might mess with them a little bit. Second, surgery most definitely messes with the surface of your cornea. Before surgery it was relatively smooth. After surgery, well, if you’re here, it’s probably mountains and valleys. Bet those slimy old mucins resent the fact that they’ve got to go crawling up mountains and down valleys. Bet they’re huffing and puffing before they make it to the tops of the mountains and maybe never even get there. Presto, dry spots. The answer? I wish I knew. Well, some of the artificial tears — but ONLY a very few - are specially formulated to try and help the mucin. That’s the only help for it that we know.

Other stuff

There’s all kinds of other stuff in your natural tears, like Substance P and lyposomes and other goodies that nourish the surface of the eye (the epithelium) and kill bugs. It’s good stuff. The more of it, the better. In fact, unless you are truly and totally dry (meaning you haven’t got anywhere near enough Watery Stuff), the fewer of those fake tears you use, the better, because they might just wash all this good stuff out of your tears.