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I can understand your concern.
Dry eye syndrome is a very common issue these days especially if you live in a cold place. Vision problems are common at the age of 40. You have not mentioned whether your visual issues are far or near. Presbyopia often sets in around the age of forty in most people. When you can read the smallest script at a distance of 9.8 inches and when your accommodation becomes weak, you will suddenly experience something similar to the double vision which is transient. Another thing, which I cannot really confirm without examining you, is the presence of a latent squint. If you break fusion (both eyes focusing simultaneously) by covering one eye, the covered eye will drift outwards.
This is different from a regular squint which is obvious all the time. So as you get older, the latent squint might cause a problem. The third possibility is severe dry eyes. As the tear film breaks up, it causes a temporary visual defect due to the diffraction of light through the broken tear film. For management, I suggest you add omega 3 to your diet which includes Flax seed powder, walnuts, fish, or taking omega 3 supplements. Secondly, talk to your ophthalmologist about lacrimal punctum plugs. These are tiny silicone plugs placed into the holes located near the inner corner of the eye that drains the tears. These plugs will prevent the tears from draining and will remain in the eye. I do not think the problem will persist once the weather settles down to a warmer climate. Use a humidifier in your home, as it will help. I cannot comment on the glasses as I have not examined you to determine if a refractive error is present or not, but you will require the OCT (optical coherence tomography) scan which will give a definitive diagnosis if there is any problem in the retina that is causing the distortion. If you have any report from the ophthalmologist, please send it as an attachment and I will reply to it.
I hope I have resolved your queries. Do get back if you have any further queries.