headaches on longhaul daylight flights

[747pilot747]

Hi,

I'm a longhaul pilot and I tend to get headaches that originiate right behind the eyes. I almost always get them on daylight flights and cannot remember ever having one on a night flight.

I wear spectacles to correct a mild case of myopia and astigmatism but I generally take them off during the cruise. I wear sunglasses if it's bright outside. I've been flying longhaul for 5 years now and I think I've always had this problem. Any ideas? I'll mention it to my AME on my next visit but maybe someone out there has some experience with this.

Thanks.