Can contact lens solution be used in place of eye drops for dry, itchy eyes?
Often, contact lens solution is just saline solution – salt water. So that would work as a substitute for eye drops. As would the cheaper & easily available water or salt water.
But not the contact lens cleaners that are sold for cleaning hard contact lens – they often contain disinfectants that would be annoying when put into your eyes (though probably just painful, no actual damage).
I always use saline solution for eye drops. The cheap stuff, even!
Depends on how itchy your eyes are. First, please don’t use the “gets the red out” kind, as they have vasoconstrictors that tend to have a rebound effect, such that you have to keep using them to keep making the red go away. They have a temporary effect only.
Many kinds of eye drops for more seriously dry eyes are thicker than plain saline, and hang around in the eye for longer with a more soothing effect. The severely dry/night time formulas may even be closer to a thick gel than a liquid. So if you find that you have to keep reapplying saline, you may have a benefit from buying the ones that are specifically for dryer than usual eyes.
Friend of mine did that once by accident. Grabbed the wrong bottle & squirted her lens cleaner into her itchy eye. Not good.
Short version: Trip to the nearby ER, lots of professional flushing, and 3 days of bright red eye and pain pills. No permanent damage, but had she lived out in the sticks or been alone it mighta been different.
That stuff is potent enough to be dangerous.
Some contact lens solution is basically dilute peroxide. Do Not be squirting that into your eye. It’ll say on the bottle whether it’s safe to put the lenses straight into your eyes without letting the solution … word blank in my head. What’s the word for finishing its reaction? It would be a type of solution with a lens case with a piece of something in it that fizzes with the peroxide.
Are you wearing your CLs while putting the solution in your eyes? That’s fine, and some “rewetting drops” for soft CLs are just repackaged CL multipurpose solution.
If you’re not wearing your contact lenses at the time, I’d like to echo what FerretHerder said about dry eye drops with different levels of viscosity. (if you put those in with the CLs in, they’re likely to hang around on the CL and lead to blurry vision. The really thick ones can lead to blurry vision even if you don’t have CLs in, so just keep that in mind. It goes away as the solution gradually drains from the ocular surface and is diluted by the tear film).
Oh, and the best ones to use, if you’re using them frequently, are the single-use capsules with a twist-off top and lubricant inside, as they do not have preservatives. Frequently bathing the cornea in preservatives isn’t always the best idea.
You can even store the capsules in the fridge for that nice cooling feeling 
Oh, and to echo what a bunch of people have said, don’t put hydrogen peroxide-based solutions like ClearCare (and others) directly in your eyes. Chances are if you use that type of solution to clean your soft lenses you’ll know, though.
And finally, since I keep remembering things I’ve left out, if your eyes are dry and itchy, you might be suffering from ocular allergies. Why not see an eye doctor? There are some very good prescription eyedrops (like Patanol) out there for ocular allergy sufferers. There are also some decent OTC ones too, such as Alaway and others.
Those were recommended after my LASIK surgery, and I used 'em by the ton. They’re marketed as “artificial tears”, which is basically what they are; they just add wetness, no “extra protection” or anything. But as a quick boost for dry eyes, they’re awesome.