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.