You should check your blood sugar level if it is within target range.
The cause for blurred vision can be a temporary eye problem that develops rapidly with diabetes and is caused by high blood sugar levels (high blood sugar in diabetes causes the lens of the eye to swell, which changes your ability to see).
Straining to see better, activates muscles around the eyes, excessively contracting, resulting in headaches.
However, you should visit your ophthalmologist, cause, blurred vision can also be a symptom of more serious eye problem with diabetes (glaucoma and cataract).
Regular ophthalmologist exams are important for diabetic people!