I have mono vision contacts, and don't wear them when sewing anymore. I badly sewed my finger a month ago, my eye doc (friend), told me to wear my regular glasses when sewing, as the single contact gives a sight distortion in lines. I can now line up my rulers when I wear my old glasses. I didn't want to progress from sewing my finger to cutting it off with the rotary cutter. A lesson learned, my finger is still sore from the chipped bone, and needle fragments.