Black flies (habitat: near fast flowing water) sand flies (obvious) and noseeums also fly into eyes. They aren't seeking your eyes, they just bumble into them. I've also had them get out of reach in my ears, fly up my nose, have inhaled them by mistake, and found them crawling into the crease between clothing and skin.
Noseeums are basically punctuation with wings. The other two are 1/8 to 3/16" long (2-4 mm)
West and Rugge in the "Complete Wilderness Paddler" have a chapter on bugs in the bush. A lighter hearted look at blackflies is here: The Blackfly Song -- Wade Hemsworth
Mosquito hats work, but make you look like an alien from another planet. In most areas blackfly season is fairly short -- bad only for 2-3 weeks. Northerners usually have a few such hats that come out as needed during the rather intense bug seasons. Sandflies seem to have a longer season. If you are traveling in bug country a full suite of armour:
* Mosquito hat. The ones with wire hoops help keep the netting away from your face, or the hoopless ones can be worn over a hat.
* Modified light weight long sleeve shirt in a medium earth tone. (Mosquitoes are somewhat attracted to blue and white) Modify the cuffs with velcro closures and gussets so that you can make a bugproof seal around your wrist. Replace/augment the button up front with velcro too. Move the collar button as needed to get a proper fit at the neck. When using bug gunk, apply to collar and cuffs.
* Nylon wind pants with elastic cuffs, and calf length zippers so you can take them on and off without removing shoes. Windpants will stop the flies, but mosquitoes will bite thorugh the fabric where it is tight against skin. Medium beige is best combination of cool and unattractive to mossies.
* two pairs of socks, one inside and one overlapping the cuffs of the wind pants.
Not all mosquito netting is noseeum proof.
Noseeums in particular are repelled by DEET, and in general DEET seems to work well on smaller flies, but as the size get larger, the effect gets smaller, and hardly works at all on horse flies.
While DEET is effective, keep it out of your eyes. Don't apply to forehead either as it runs with sweat into your eyes and stings. Applying to hair (if you still have it...) works, as does applying it to the edges of your hat.
Deer flies and horseflies however do not like a greasy surface. I knew of a crew setting hydro pylons on the east side of Lake Winnipeg (Lines from Limestone Point/Kettle Falls dams) who wanted to work without shirts due to heat and humidity. They found that slathering themselves with motor oil was effective. On hearing this tale, I experimented with lard. It works. They still do touch and go landings, but do not bite.