North Western Hot snake vs Non-venomous snakes?

[ErikBush97]

So I heard something very interesting today. I heard that in N.W. U.S.A you can tell the difference between a hot snake and a non venomous snake by the eyes... it was online so I am just wondering if thats true or BS? The guy said that if a snake in the N.W has a slit in the eye, it's hot, and if not, it's non venomous. Is that true? I am pretty familiar with all 15 types of our native snakes here and Oregon and I think the Diamond back is our only hot snake. I am not going to look at an unknown snakes eyes and pick him up either way but that is still pretty interesting to me. The first pic is of the slit shaped pupal I mentioned which is supposed to indicate that the snake is hot (Diamondback to be specific). The second is the eye of a non venomous colubrid (Gopher snake).
Edit: I'd like to know whether thats completely false, true for some N.W snake, or true for all. So if I'm walking down a trail and I see a snake without those slits am I okay to be around it or could it be hot?