As someone who has a continuously worsening astigmatism caused by eye trauma, I have noticed this, as well. And many times I will get beaches or migraines the next day from eye strain using the lower-quality glass for hours on-end at the range. For years I never put 2+2 together, until I used nothing but some of my high end scopes all day on the range, and had zero migraine or headache the next day. Then I tried it again the following week with cheap scopes, and headache that night or the next day.