Let’s talk a little bit about hyaluronidase. Hyaluronidase enhances the spread of Local Anesthesia with Ophthalmic blocks

Hyaluronidase is the enzyme that breaks down hyaluron or hyaluronic acid, a polysaccharide found in connective tissue. 

Hyaluron is present throughout the human body where friction and or movements occur. (Koornneef) 

Thus it is no surprise that we find Hyaluron making up the dense matrix of connective tissue of the orbit and retrobulbar space. (Singh)

The enzyme, Hyaluronidase, hydrolyzes the hyaluronic acid, in the retrobulbar space behind the globe, increasing the permeability through the connective tissue and allowing a more uniform distribution of the local anesthetics in the orbit. Hyaluronic acid or hyaluron regenerates itself in about 48 hours.

I use 2-3 units of hyaluronidase / ml of LA in my Peri-Retrobulbar Intraconal Blocks and see an effective LA onset 1-minute after I complete the block.

Hyaluronidase is manufactured from 3-different sources, bovine, ovine and human recombinant. 

It is important to know the different types of medications or combinations of medications available to you as a clinician, and how they may or may not affect each patient. For more detailed information about Hyaluronidase, check out my accredited course Pharmacology for Ophthalmic Blocks. https://orbitalblocks.com/collections/frontpage 

References:

Koornneef L. ConnectiveTIissue Apparatus of The Human Orbit. What  About It? 

Proc. 3rd Int. Symp. on Orbital Disorders, Amsterdam, 1977.

Sing, SP & M. Nikifosak. The Biochemical Composition of Human Retrobulbar Connective Tissue. Separate Experiments Vol. 32, pp.395-396,

Berkhauser, Basel ,1976.

Retrobulbar Orbital Anatomy

The literature defines Peribulbar Blocks as Extraconal and the Retrobulbar Blocks as Intraconal. However, these definitions do not correlate with the anatomical path of the needle tip during the block.

Anatomical Definitions

• Peri is defined as about or around and Bulbar as of or pertaining to the eyeball. Thus anything that is around the eye is Peribulbar
• Retro is defined as behind. The retrobulbar area is situated or occurring behind the eyeball.
• Intraconal is defined as the area inside the muscle cone 
• Extraconal is defined as the area external to the muscle cone.

For example: Unless the needle tip is inside the globe, all blocks are peribulbar. Any time the needle tip goes behind the globe you are retrobulbar Intraconal or Extraconal needle tip placement is determined by the angle and depth you insert your needle tip into the orbital area.

Anatomically most blocks performed by an anatomical definition would be described as about or around and posterior to the globe which would define the ophthalmic blocks as both Peribulbar/Retrobulbar.

The literature reports ocular and orbital injuries from both Peribulbar and Retrobulbar blocks, so it is misleading to state that the Peribulbar Block is safer than a Retrobulbar block. 

An article in 1983 by Gills-Lloyd described the parallel approach to intraconal retrobulbar Blocks. Analyzing this needle track to the mid orbit demonstrates a lack of vital orbital structures along the projected needle path except the globe. However, Gills and Loyd do not address the needle insertion depth around the globe before redirecting the needle tip into the intraconal space. 

In 2008 I presented a poster presentation at the annual meeting of the Ophthalmic Anesthesia Society entitled, “A Geometrical Method Applied to an Orbital block”. This approach measures the dynamic orbital-globe relationship, calculates the distance from the needle tip insertion site to the equator of the globe and geometrically standardizes the technique for more precise performance and teaching the technique to other practitioners. 

Dr. D’Agostino and myself developed a video of the technique, which was accepted by the American Academy of Ophthalmology in 2013 to their Network-1 website. You may also view the video at www.orbitalblocks.com. 

We invite you to visit http://www.orbitalblocks.com and learn more about both intraconal and extraconal ophthalmic block techniques and retrobulbar vs peribulbar. Each individual online course is accredited for physicians and CRNAs and can be taken at anytime you need the didactic training to perform ophthalmic blocks and/or continuing education in ophthalmic anesthesia.

References

Gills JP, Loyd TL. A Technique of Retrobulbar Block with Paralysis of the 

Orbicualris Oculi. J Am Intraocul Implant Soc. 9(3): 339-40, Summer 1983.

Harvey R. A Geometrical Method Applied to an Orbital Block. Poster Presentation, Ophthalmic Anesthesia Society Annual Meeting 2008.

Harvey R & D’Agostino E. A Safe and Effective Peri/Retrobulbar Block Technique. Network-1 website, American Academy of Ophthalmology, 2013.

Disclaimer: The purpose of this blog post is for medical education only.  It is not intended as and does not substitute for medical advice. Information posted should not be construed as personal medical advice. Posts are not intended to diagnose, treat, or cure disease. The goal is to inform the audience with interesting medical and community information for strictly educational/entertainment purposes only.

We understand there are a variety of ways to actually perform orbital regional anesthesia. Therefore, it is extremely important as a clinician, that you have a very good understanding of the complex orbital anatomy. 

In conjunction with Bio-digital’s 3-D platform, we have developed a guided virtual tour of the orbital anatomy, which includes both a lecture based review of the orbital anatomy and also allows you to further your understanding through individual use of the 3-D model.

Once you have obtained an in-depth understanding of the orbital anatomy, you will be able to mentally picture your needle-tips pathway from the insertion site to the needle-tips end point.

This knowledge will allow you, the practitioner, to discern between the multiple approaches to orbital regional anesthesia and utilize techniques that you find the safest for your patients.

For example, the standard retrobulbar injection by Atkinson directs the needle tip towards the orbital apex from its inferotemporal insertion site. Anatomically the needle tip is in line with the macula, the optic nerve and larger orbital vessels with needles 1 ¼” to 1 ½”.

Our understanding of the orbital anatomy has already led to the abandonment of Atkinson’s “Look-up and In” position of the globe.

We will explore both intraconal and extraconal orbital block techniques that avoid these vital orbital structures and provide satisfactory anesthesia for ophthalmic surgical procedures.

By tracking both the intraconal and extraconal motor and sensory cranial nerve roots of the orbit, it will help us to understand where we can achieve the most effective local anesthetic distribution in the orbit.

Start Now and take advantage of the in depth information and guided virtual experience provided so that you can make the best and safest decisions in your practice.