They always say one sign of diabetes is blurry vision. how does that work? how are they related?

Lens swelling: Elevated blood sugar can result in swelling of the intraocular lens. Typically, this increases the power of the lens, making you more nearsighted. Normalization of blood sugar levels will usually reverse the swelling. If you are diabetic and noticing vision changes, you should, of course, see your ophthalmologist.

Lens swelling: High sugars cause the lens of the eye to swell causing the eye to become more nearsighted.