Can map-dot corneal dystrophy cause your eyeglass prescription to vary over the course of several days or weeks?

Yes. Epithelial basement membrane dystrophy, or map-dot fingerprint dystrophy, is caused by irregular adherence of the corneal epithelium (outermost layer of cornea) to the underlying tissue. These irregularities on the surface of your eye can cause changes in your vision and your prescription. Most of the time, repeated measurements of your prescription on different visits will give you a close approximation of your true prescription. However, if the changes are excessive, you can discuss with your eye doctor if removal of these irregularities is a good idea.