I don’t know about my fellow T1D’s experience, but there is a small change that I always observe during summers every year and that is a slight ‘Blurred vision’. 

At first, when we hear or experience blurry vision, the first thing that comes to our mind is, that something is very wrong with our eyes and is very obvious. A few years back, when I started realizing that I have a slight blurred vision during summers, I asked my ophthalmologist about the same during my annual checkup and he said that its quite common in people with diabetes to have a bit unclear vision during summers. Its very obvious that he examined my eyes first, as he had to rule out other possibilities too. I got my Intra ocular pressure done and thorough examination, so as to check for any signs of retinopathy. 

As I had undergone my LASIK surgery a couple of years ago, he asked me to use a simple eye drop meant for lubrication of eyes and that was all. The basic idea behind prescribing those eye drops was simply preventing dryness and keeping my eyes moist which was hampering my vision. After that, during every summers when temperatures really take toll, I get those eyedrops (as prescribed by him) and use whenever I feel like and vision is as clear as any other day.

Note :

1. Please do not consider this as medical advice and always visit your ophthalmologist if you have a blurred vision, as this can be an early sign of glaucoma or retinopathy or something else. 
2. Never use any eye drop without consulting any ophthalmologist or on advice of any of the pharmacist, as eyes are a very sensitive part of your body.

*This is very common with almost all the T1Ds, still rule out other possibilities first and then make any generalization as I did.