This is sound advice, our ophthalmologist said the same: glucose level can change the thickness of your cornea (https://pubmed.ncbi.nlm.nih.gov/17964654/ https:

This is sound advice, our ophthalmologist said the same: glucose level can change the thickness of your cornea (https://pubmed.ncbi.nlm.nih.gov/17964654/ https://pubmed.ncbi.nlm.nih.gov/17964654/), and that can even improve your vision. A sudden change in vision, for the worse or better, merits checking your glucose level.