The underlying cause of blurred vision is a change in the metabolism of the lens of the eye resulting from high blood sugar. This temporarily changes the refractive power of the eye.
How the situation is experienced depends on the previous refractive power of the eyes: a person with age-related farsightedness may suddenly have better near vision, while someone who uses reading glasses may see better without them. Someone who previously had normal vision becomes short-sighted, and the long sight of someone who was short-sighted to begin with deteriorates further – person can still see things near them without glasses but closer than before.
Such a deterioration of the eyesight can feel scary. It is important to know that this is not a permanent change. Once the blood sugar level has been corrected by the treatment, these disturbances of vision will also correct themselves within a few weeks.
It is good to be aware of the deterioration of eyesight as a diabetes symptom as it may be the first symptom of diabetes, which makes person to see a doctor.
There is no point getting glasses when diabetes is first diagnosed or for a couple of months after the start of treatment.