Retrobulbar blocks have been used for decades to anesthetize the eye and orbit in the case of intractable pain or for surgeries. There is also new buzz about learning retrobulbar blocks in order to administer high doses of hyaluronidase in the rare case of central retinal artery occlusion after dermal filler injection. Whatever the intention, it is paramount to have the skill and knowledge before administering one of these blocks, as they do not go without risk and serious consequences.
Know Your Needles
Knowledge of both orbital and ocular anatomy is essential prior to putting a needle back there. The floor of the orbit slopes in an upward direction of about 10 degrees. The orbital apex, where the most essential nerves, muscles and vessels arise, is angled toward the nose.
Traditionally the thought was to insert the needle at the junction of the lateral 1/3 and medial 2/3 of the inferior orbital rim. The current trend is to move a bit more laterally, around the junction of the lateral ¼ and medial ¾ in order to avoid post injection strabismus.
Use a needle that is no longer than 1 ¼ inches in length. Longer needles will reach too far toward the apex and can cause serious damage, such as brain stem infiltration, strabismus, and intra-arterial injection. Some choose to use blunted needles so they are less likely to penetrate important structures such as the globe or optic nerve. The gauge of the needle can be any size between 23 and 27.
Peribulbar Blocks vs. Retrobulbar Blocks
Many have switched to giving peribulbar blocks rather than retrobulbar blocks for operative anesthesia. In this case, a shorter needle can be used and the angle of the needle pointed straight back, rather than angled toward the nose.
In a peribulbar block, the lower lid skin is infiltrated, whereas in a retrobulbar block the upper eyelid skin balloons up and you should see gradual loss of the eyelid crease. Digital pressure on the lower lid/inferior orbital rim will help guide the fluid toward the apex. The needle should be aimed straight back, then once past the equator of the globe, can be angled a bit more medially toward the apex. The patient should always be looking straight ahead, as upward gaze puts the optic nerve in the path of danger.
These are just a few tips for giving retrobulbar blocks that hopefully are useful to the caregiver.