Why Did I End Up in the Emergency Room After Botox Injections?

Another rare but possible complication after Botox injection to the "crow's feet" is decreased tear production. If Botox is injected near the lacrimal gland (which resides deep to the outer edge of the upper eyelid), this gland which helps to lubricate the surface of the eye may produce less tears. This effect has been shown to last for 6 months when injected directly into the gland. In someone who has dry eyes to begin with, this could cause worsening of the condition and blurry vision. Luckily, these effects should be temporary.
That being said, Botox is very safe and has a longstanding history of high patient satisfaction and a very low complication rate when properly administered.

Misplaced botulinum toxin can cause visual disturbance by affecting the muscles that coordinate eye movement. All three of the neuromodulators that are commonly used and FDA approved for cosmetic use in the US (Botox, Dysport, Xeomin) are extremely safe, when in the right hands. 
Any horror stories that you hear are likely performed by unlicensed providers at a medi spa, home injection party, dentists office, etc. 
When put in improper places with incorrect doses, problems can definitely happen.
These unqualified injectors, although especially prevalent where I practice, are everywhere across the US. Choose somebody whose entire practice revolves around facial anatomy, facial cosmetics, and who's training was specific to that - this is not your cardiologist or geriatrician who took a few weekend courses. Stay away from the dentist, internal medicine doctor, family practice doctor, etc who decided to inject Botox on the side to make a few extra bucks. You often find the best deals with these unqualified providers or medi spa's, but you will get what you pay for in the end.  
It is also worth noting that just because somewhere does a lot of Botox does not necessarily mean they are good at it; doing the same thing wrong a thousand times just makes one better at doing it wrong.

Scientifically: 
Botulinum toxin was first isolated in the 20s, was first used therapeutically in 1968, and became approved in 1989 for eye issues. It has been used heavily for cosmetic use since 2002, and it was the first aesthetic drug ever approved.  All that is to say...it has a lot of safety data behind it. Recent evidence (coming out this week) proves that botulinum toxin does NOT enter your brain as it's distant cousin tetanus toxin does, which is where that theory came from. 
Botox, Dysport and Xeomin are the 3 botulinum toxins approved for cosmetic use in the US. They all work in the same way, at the presynaptic terminal blocking the release of acetylcholine - making the nerve temporarily unable to communicate with the muscle. It is broken down as a protein in our body with liver metabolism. Effects are temporary, and repeated use serves to take tension off of your skin, relaxing lines and wrinkles.
To ensure you are receiving the highest level of care, seek out a modernly trained, new-school dermatologic surgeon, oculoplastic surgeon, facial plastic surgeon or plastic surgeon who is board certified and fellowship trained in one of these "core four" cosmetic specialties. Membership in organizations like the American Academy of Facial Plastic and Reconstructive Surgery help to identify a highly trained surgeon.
Cameron Chesnut
#realself500 Physician

Sorry that you had such a negative experience. Botox adversely affecting the vision is normally caused by one of two primary reasons.  Injector error due to improper technique or improper location. Or, not genuine botox was used. The decision to place botox near the lower lash line is generally unwise as it can affect two muscles -  Orbicularis Oculi muscle and Inferior Oblique muscle.  If the inferior oblique muscle was affected then the patient may experience double vision. If the Orbicularis Oculi muscle was affected the function of the lower lid may have been impacted. Your experience demonstrates the need to go to only experienced and expert physician injectors.