I hope you get your eyes checked pronto. Get good quality sunglasses. They don't have to be cycling specific, but they should protect from UVA and UVB rays (cheap ones usually don't and are worse than no sunglasses) and should also protect the sides of your eyes. They should also be made of polycarbonate--you don't want any shattering to go on around the eyes. There are lots of sports sunglasses out there that have these components. I like my Rx Tifosi sunglasses very much.

I used to think that plain water was fine for any ride under two hours. Then I started drinking electrolyte drinks (diluted) and felt so much better during and after rides, even shorter rides. It's also important to be hydrated throughout the day, not just before and during rides.

I've gotten headaches when my helmet's been too tight. My helmet has a little knob in the back that makes it easy to adjust the tightness. Very helpful.

I also would suggest that you see a doctor or neurologist in addition to getting your eyes taken care of. Just cover all the bases.