“If I have dry eyes, why are they watering so much?”
This question comes up very frequently in my exam lane, and I am always happy when it does. A successful treatment plan for dry eyes initially begins by prescribing a good dose of education. However, the education that I can provide in the exam room can be a bit overwhelming, and the last thing I want is for my patients to think that I misunderstand their symptoms, or their treatment plan. So, in this post, I hope to add a little more clarity to the mechanisms involved in creating “watery, dry eyes.”
The tears that cover our eyes (the “tear film”) throughout each day and night, giving them a shiny-looking surface, are not only comprised of salty water. There are actually three different components to a healthy tear film. 
First, there is a layer of protein, mucin, which lines the surface of the eyes. This protein acts as a point of adherence for the second part of the tear film – the salty, or aqueous, portion of our tears. This liquid accounts for over 90% of our tear film. Finally, the outermost layer of the tear film is a thin layer of oil, or meibum. Even though it is very thin, it is the most important stabilizing factor of our tears. It functions similarly to the action that allows liquid bubble-solution to stand up vertically in the bubble-blowing wand.
The tear film is essentially a vertical wall of water. I’m not sure if you’ve noticed, but water on the surface of the earth likes to spread out horizontally, not vertically. If there is not an adequate amount of oil, our tears will seek the lowest horizontal place to rest – the lower eyelid. This will cause a larger amount of tears on the lower eyelid that may not be able to be drained away quickly enough and might spill over the edge of the eyelid. Additionally, the perfect tear film is in place to defend the surface of the eye, which is packed with pain receptors, from dust and airborne particles that could damage the eye. 
If the tear film is mostly resting on the lower eyelid, it is more likely that particles could land on the surface of the eye and trigger excessive tearing as a response. It is in this response that the tears overwhelm the normal drainage system and spill over the edge of the eyelid onto the face.
Fortunately, it can be relatively simple to improve the quality of the tear film. There is a type of artificial tear that has a tear stabilizer in it. It is called an emollient artificial tear. These tears have an added oil component and are often milky or cloudy in appearance. The additional oil may cause you to have some blurry vision for a minute or two after instilling the drop into the eye. However, these drops are merely acting to fix a symptom of the underlying problem. They will decrease tearing, and may make the eye feel better temporarily, but they will not fix the problem.
Fixing the underlying problem is often more involved but also quite possible.
There are a number of effective treatments for improving the quality of your tears. To determine which treatments are most likely to be effective for your particular tear-quality issue, it will be necessary to be examined by an eye care practitioner.
…I happen to know a good one, in case you’re interested!
Pursing the best of health,
Dr. Tim