A problem is that during the subjective measuring the optometrists reduce the strength until your vision get worse. But astigmatism does not affect the vision

A problem is that during the subjective measuring the optometrists reduce the strength until your vision get worse. But astigmatism does not affect the vision so much. Then they get, you have 20/20 vision with the correct glasses, and 20/20 vision with weaker glasses, so they give you weaker glasses, even though they cause some blurriness