I was Vit-D deficient living in California, so I'm certain I'm Vit-D deficient living in Canda. My doc in Canada doesn't run a Vit-D panel - He says everyone needs to take Vit-D here. But Vit-D tabs don't seem to do much for me.
Here's my story. I play volleyball and have been playing pretty serious vball for the last 2-3 years. I started having double vision after about an hour or an hour and a half of play, I believe, due to dry eyes. I started doing nasal irrigation before my games, and that seemed to take care of this problem up to a point. (I drink tons of fluid, hydrate myself with electrolytes, etc but they didn't seem to do much to alleviate the double vision for some reason.) I don't want to get into all the experiments I did to finally get to this conclusion, so to make the story short, I started going to a tanning salon to replenish my Vit-D. I only do 8 minutes once a week or so on average, and I cover my face and my hands because I don't want any extra wrinkles in this area. I am tanning slightly (I'm Asian) even with just 8 minutes of use of the tanning bed.
Anyway, my double vision is completely gone. No nasal irrigation, nothing and it's just gone. I didn't do the tanning for 2 weeks and my double vision came back after 2.5-3 hours of pretty intense vball (tournament) so I'm trying to do 8 minutes once a week.
I started tanning in the winter months to keep my winter blues away and this eye thing is just a nice, added benefit. I didn't know that Vit-D had any impact on the eyes.