Are your glasses polarized?

Are they 100% UVA and 100% UVB?

The darkenss of the shading is only a small part of what makes quality eyeware for flying. Polarized glasses make a HUGE difference, and UV protection should be a no-brainer, with out it, you run an increased risk of developing cataracts.

Yellow or brown tints often help sharpen what you see a little as well.

Also, if it's been as hot there as it has here, are you drinking lots of water at the field? How about food? I get more of a headache at the field when I forget to eat or drink enough than I do from the sun in the eyes these days.