[Sacamuelas]

Tough one for the internet Bbdb.

Lots of potential causes of "blurry vision" in one eye. I will base my post on the assumption that you mean it is blurry because of the excess tearing. If not, then disregard this info.

Since you are asking for guesses.... I will give thoughts but please understand that I am not recommending you see an ENT for specific testing for this diagnosis. Talk with your Doctor about it and use him/her to guide your treatment.

Summary-
Your symptoms are of a "watery eye" only during a sinus infection/congestion and only affect the same eye right? It happens every time you have serious sinus congestion correct?

With that info, I would lean against a medication induced vision problem, as they would tend to affect both eyes similarly.

I see it in main possibilities:
1. An alteration in the composition of your tear production that is leading to either excess flow or altered mucous/water composition. This could be caused by taking medications to treat your congestion in your sinuses.

2. (my best guess) You are experiencing mild Nasolacrimal duct blockage in your left eye. This is the duct that drains the tears from your eyes down through into your nasal cavity. If your sinus inflammation is severe enough, it could cause a partial blockage of the NLD that would produce the symptoms you have.

The reason I like this diagnosis is it tends to fit your (recurrent- left eye only -sinus congestion only) scenario. The ducts for the left and right eye are separate entities. Each travels its own path into the sinuses. Therefore, it is possible that your left NLD could have narrowed over time, become partially blocked by a polyp, or be more susceptible to this blockage due to the anatomy in that side of your nasal sinuses. Also, it only affects you when your sinuses are "blocked" or congested due to membrane inflammation. One duct could easily become blocked by inflammation of the sinus lining more than the other NLD based on your specific nasal anatomy. Your repeated problem with only the left tends to follow that pattern.

If your Doc decided this could be the problem, specific testing can be done to determine blockage and quantify your "drainage system" of each eye.

That is my educated guess... I must say that this is something that is difficult if not impossible to ID over the net. Maybe others on here can help.

Here. Stole a pic to give you an understanding of the NLD system.