Recently, I got a call from a dentist friend of mine.
He told me that he had administered Posterior superior nerve block and extracted a grade 3 mobile right maxillary first molar.
It took him hardly 5 minutes to complete the extraction. But the patient started complaining of double vision.
On clinical check-up, it was found that the patient did have double vision especially on looking sideways towards the right side.
I asked him not to worry and assured him that it should subside within a few hours as the effect of Local Anesthesia wears off.
In India, there is a misconception among the general public that getting any dental treatment done may lead to weakening or loss of eyesight.
We dentists usually dismiss it as superstition due to lack of education among the general population. But we tend to forget that many of these superstitions started from a logical base.
Remember this, there can be ocular complications due to the administration of Local Anesthesia (especially Inferior Alveolar & Posterior Superior Alveolar Nerve Block) but never due to a dental procedure.
As Local Anesthesia is required in most of the dental procedures, the patient usually associates the ocular complication with the dental treatment.
The exact reason is still not clear as to how the injection of Local anesthetic leads to ocular complications but there are a few theories that explain it.
So, let’s get started.
Some Anatomy First
Inferior alveolar artery is close to the site of injection for Inferior Alveolar Nerve Block.
Maxillary Artery, Posterior Superior Alveolar Artery & Pterygoid plexus are present close to the site of injection of Posterior Superior Alveolar Nerve Block.
When administering Inferior Alveolar Nerve Block & Posterior Superior Alveolar Nerve Block, the operator may accidentally deposit Local Anesthesia into the lumen of these arteries or in the Pterygoid Plexus.
This may happen even after bi-planar aspiration, due to slight movement of the patient or the operator.
If the Local Anesthetic is deposited with pressure inside the lumen of these blood vessels (artery or pterygoid plexus), that may cause a retrograde (backward) flow of the Local Anesthetic via different pathways finally ending at the structures related to the eye.
Inferior Alveolar Nerve Block
When the Local Anesthetic is deposited with pressure inside the lumen of the Inferior Alveolar Artery, there is a backward flow of Local Anesthetic to the main trunk of the Maxillary Artery.
From there Local Anesthetic is pushed into the other branches of the Maxillary Artery, one of which is Middle Meningeal Artery.
Middle Meningeal Artery is connected to the Recurrent meningeal branch of the Lacrimal Artery. Lacrimal Artery supplies the Lateral Rectus muscle of the eye. Hence the Local Anesthetic reaches the Lateral rectus muscle & paralyzes it.
Lateral Rectus muscles cause lateral rotation of the eye. So, the patient will have diplopia, especially on viewing laterally.
Posterior Superior Alveolar Nerve Block
When Posterior Superior Alveolar Nerve Block is administered, there are chances of accidental deposition of Local Anesthetic into the lumen of the Main trunk of Maxillary Artery, Posterior Superior Alveolar Artery or Pterygoid Plexus.
If Local Anesthetic is deposited in the lumen of the Posterior Superior Alveolar Artery then the solution will be pushed into the Main trunk of the Maxillary Artery.
From the Main trunk of the Maxillary Artery the Local Anesthetic flows to Middle Meningeal Artery and finally it reaches the lacrimal artery via the Recurrent meningeal branch of the Lacrimal Artery.
This leads to diplopia.
If Local Anesthetic is deposited in Pterygoid Plexus then there will be backward flow of Local Anesthetic via the emissary veins to the Cavernous sinus.
So, the Local Anesthetic solution flows from the cavernous sinus to these structures. This leads to complications such as diplopia, Mydriasis, blurred vision, amaurosis (temporary blindness).
Another reason would be direct diffusion of Local Anesthetic from infratemporal fossa to pterygopalatine fossa and from there to inferior orbital fissure. This diffusion if further facilitated by supine position of the patient.
The abducens nerve lies close to the inferior orbital fissure. Hence Abducens nerve is directly exposed to the Local Anesthetic solution, leading to diplopia.
Also, the chances of ocular complications are more in females than in males. The reason for this is that the size of the skull in females is smaller than males, so Local Anesthetic has to travel less distance to reach the eye.
Management
Reassure the patient regarding the usually transient nature of the complications.
The symptoms usually are present for the duration of action of Local Anesthetic. Although rare cases of permanent damage have also been reported.
Cover the affected eye with a gauze dressing to protect the cornea for the duration of Anesthesia.
The patient should be discharged from the clinic only when he is escorted by a responsible adult. This is to prevent the patient from doing any motor activity like driving, as depth & distance perception is hampered by the ocular complication in one eye.
Follow-up the patient after 6 hours, if the symptoms still persist then refer the patient to an ophthalmologist.
Remember a good doctor knows how to manage a complication, but a great doctor knows that it is best to avoid it.
So read the next section to be a great doctor.
Prevention
Biplanar aspiration with minimal antero-posterior movement to avoid injection into the lumen of a blood vessel.
Slow injection rate is mandatory. Even if the needle bevel is inside the lumen of a blood vessel, the slow rate of injection leads to less pressure. Hence there is no backward flow of Local Anesthetic.
IMPORTANT
Guys. After i had published the article, i realized that i have made a mistake in some pics. Maxillary artery branches from External Carotid artery & not Common Carotid artery. External carotid artery branches off from Common Carotid artery.
So now you know that sometimes when the patient says that he has difficulty in seeing or he has double vision after dental treatment, he may actually be telling truth.
Let me know in the comment section, whether you have experienced any such ocular complication and how you managed it.