Imagine going to the dentist for a filling and then suddenly going blind while in the chair. That’s what happened to one man who went in for a root canal. Before the dentist even started drilling, the man had a sudden loss of vision. Here's a case report of what happened.

A recent article in the Journal of Endodontics described the case of a 37-year-old man whose 2-week-long toothache sent him to the local dental college. The dentist who examined him observed a large cavity in his right first molar. An x-ray of the tooth showed a deep cavity that went all the way to the root. The dentist recommended a root canal, and the patient agreed to have it done at that visit.

The dentist used a 30-mm-long, 28-gauge aspirating syringe to administer anesthesia (1.8-mL lidocaine with 1:100,000 adrenaline) targeting the right inferior alveolar nerve. Aspiration was negative.

Immediately after receiving the anesthesia, the patient reported blurred vision in his right eye. About 30 seconds later, he said that his vision was completely gone.

Sudden vision loss

The dentist stopped the procedure immediately and reassured the worried patient while keeping the man lying in the chair as relaxed as possible. The patient’s vital signs showed no changes, and he was mentally alert. The dentist performed a quick ocular motility test, which revealed normal eye movement in all directions.

The dentist then asked the patient to read a nearby letter chart, covering one eye and then the other. The man’s vision was normal in his left eye, but he had no vision in his right eye. Other than this, the patient showed no physical symptoms or changes in speech or mental acuity.

After a long 15 minutes in the chair, the patient regained vision in his right eye. He said that his visual acuity was still poor in that eye, but after 30 minutes that too resolved. The patient remained in the clinic 1 additional hour for monitoring, which was uneventful, and then the dentist discharged him.

At a follow-up visit 2 days later, the man reported no problems since leaving the clinic. The dentist went ahead with the root canal under local anesthesia—and this time the patient suffered no vision loss.

What happened?

Why did this patient have a sudden loss of vision? Surely, you’ve concluded that it had something to do with the anesthetic injection—but what was it specifically? Was it a drug interaction with the anesthetic itself, or maybe even with the tiny bit of adrenaline? Was it the injection approach, or was it perhaps the location of the injection site?

Sudden vision loss (amaurosis) after inferior alveolar nerve anesthesia injection is rare but not unheard of. It’s often accompanied by diplopia. Among the few cases reported in the literature, amaurosis usually resolved on its own in about 20-30 minutes. Only two case reports have described permanent vision loss.

The prevailing explanation for this temporary amaurosis goes like this: Because the inferior alveolar artery lies adjacent to the inferior alveolar nerve, accidental administration of a local anesthetic under pressure forces the solution into the artery, and backflow carries it into the maxillary artery and middle meningeal artery, where it’s eventually delivered into the central artery of the retina. The result: blurred vision and/or temporary vision loss.

“Although the initial aspiration showed a negative finding in our case, minor movement of the patient and the syringe could lead to the penetration of the needle into the wall of the artery with subsequent deposition of the local anesthetic solution,” wrote the authors of this case report. “Given that the patient reported complete loss of vision and loss of visual acuity immediately after the administration of the intraoral local anesthesia, it can be postulated that the combination of intra-arterial injection and anatomic variation is responsible for this event.”

How can you prevent such a worrisome misadventure the next time you or a loved one visits the dentist? Frighteningly enough, you should ask for a big needle—a smaller-gauge needle is more likely to be deflected when passing through the tissues. And don’t move a muscle when the dentist injects it. Although this may be more uncomfortable, it’s better than going blind.

This story is contributed by John Murphy and is a part of our Global Content Initiative, where we feature selected stories from our Global network which we believe would be most useful and informative to our doctor members.