What would happen if somebody used eyedrops laced with heavy doses of novocaine (or any of the other -caine drugs) or eugenol (active ingredient in clove oil)? Would they be temporarily blind, or just see everything as a blur (due to paralysis of focusing muscles)?
Proparacaine is used all the time as a topical eyedrop. It numbs the eye, as you would expect. This can be used prior to surgery or to certain procedures (like tonometry, or eye pressure measurement).
It does not cause paralysis of the ciliary body (the muscle in the eye involved in focusing.) Other drops (mydriatics) can do so, however.
Topical anesthetic use is common. The vision is not affected.
However, use of these products for more than 24 hours reduces the cornea’s ability to absorb oxygen from the air (that’s how corneal cells get oxygen because capillaries running thru the cornea to supply oxygen would interfere with vision), and can cause corneal ulceration, perforation, and the need for a corneal transplant.
It is also worth pointing out that anesthetizing the cornea is playing with fire. Without the sensation of pain, or even discomfort to warn you, it is very easy to do very serious damage to it. In fact, I was taught that unless you’re using an ultra-short-acting anesthetic, then to avoid such trauma, you must place a patch over the anesthetized eye until sensation has been restored.
True dat! 
No idea, other than when that happens, it’s a damn weird experience.
I was due to have knee surgery, and the anesthesiologist was explaining all the drugs he was administering, and he got to the muscle relaxant, and said “your vision may get blurry”.
He wasn’t kidding- it was almost instantaneous. I went from being able to focus on things, to totally relaxed, to the point where I couldn’t even focus my eyes!
Cocaine was used an optical anesthetic at one point and IIRC can still be used (though I think if it’s still used, it’s used more as a nasal anesthetic).
It is used as a nasal anesthetic, I handle it a few times a month for ENT surgeries. I’ve never seen it used in the eye.
My mom was an early adopter of hard contact lenses (early-70s). Before fitting them for the first time the optometrist put anesthetic drops into her eyes. Hard contacts hurt like hell the first time you try them…
I had numbing drops when I had my laser iridotomy. It felt odd, but I don’t recall any vision issues between the drops and the start of the procedure. My vision was a little weird after the fact for a few hours (focus was fine, but the lighting seemed dimmer and yellower than I remember). I could see ok, though.