A retrobulbar block is a
regional anesthetic nerve block
Nerve block or regional nerve blockade is any deliberate interruption of signals traveling along a nerve, often for the purpose of pain relief. Local anesthetic nerve block (sometimes referred to as simply "nerve block") is a short-term block, ...
in the retrobulbar space, the area located behind the globe of the
eye. Injection of local anesthetic into this space constitutes the retrobulbar block. This injection provides
akinesia
Hypokinesia is one of the classifications of movement disorders, and refers to decreased bodily movement. Hypokinesia is characterized by a partial or complete loss of muscle movement due to a disruption in the basal ganglia. Hypokinesia is a sym ...
of the
extraocular muscle
The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the oth ...
s by blocking
cranial nerves
II,
III, and
VI, thereby preventing movement of the globe. Cranial nerve
IV lies outside the muscle cone, and therefore is not affected by the local anesthesia. As a result, intorsion of the eye is still possible. It also provides sensory anesthesia of the
conjunctiva
The conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epithelium ...
,
cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...
and
uvea
The uvea (; Lat. ''uva'', "grape"), also called the ''uveal layer'', ''uveal coat'', ''uveal tract'', ''vascular tunic'' or ''vascular layer'' is the pigmented middle of the three concentric layers that make up an eye.
History and etymolog ...
by blocking the
ciliary nerves. This block is most commonly employed for
cataract surgery
Cataract surgery, also called lens replacement surgery, is the removal of the natural lens of the eye (also called "crystalline lens") that has developed an opacification, which is referred to as a cataract, and its replacement with an intra ...
, but also provides anesthesia for other intraocular surgeries.
Side effects and complications
Complications associated with this block are either ocular or systemic. Local ocular complications include
hematoma formation,
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...
damage and perforation of the globe with possible blindness. Systemic complications include
local anesthetic toxicity
A local anesthetic (LA) is a medication that causes absence of pain sensation. In the context of surgery, a local anesthetic creates an absence of pain in a specific location of the body without a loss of consciousness, as opposed to a general an ...
, brainstem anesthesia, and stimulation of the
oculocardiac reflex. Most commonly, patients will report discomfort during the performance of the block, such as the sensation of the needle during insertion and/or pressure behind the eye during injection. In recent years,
peribulbar block has become increasingly used because of its lower incidence of complications.
Technique
Resuscitative equipment, monitoring and personnel must be immediately available prior to performance of this block. The retrobulbar block is performed with the patient either seated or supine and looking straight ahead. The head should be maintained in a neutral position. A needle (22–27 Gauge, 3 cm long) is inserted at the inferolateral border of the bony orbit and directed straight back until it has passed the equator of the globe. It is then directed medially and cephalad toward the apex of the orbit. Occasionally a 'pop' is felt as the needle tip passes through the muscle cone delineating the retrobulbar space. Following a negative aspiration for blood, 2–4 mLs of local anesthetic solution is injected and the needle is withdrawn. 2%
Lidocaine (Xylocaine) and 0.5% to 0.75%
bupivicaine (Marcaine) are two commonly used agents. Epinephrine, commonly mixed in with local anesthetics for vasoconstriction, is not used in seeing eyes as this can cause a central retinal artery occlusion. An enzyme,
hyaluronidase
Hyaluronidases are a family of enzymes that catalyse the degradation of hyaluronic acid (HA). Karl Meyer classified these enzymes in 1971, into three distinct groups, a scheme based on the enzyme reaction products. The three main types of hyal ...
, is frequently a component of the anaesthetic solution, as it accelerates and improves dispersal of the agent. Akinesia and anesthesia quickly ensue within minutes with a successful retrobulbar injection.
Retrobulbar block can be used successfully for corneal transplantation but may require a supplemental facial nerve block. Retrobulbar block can block levator palpebrae muscle but not orbicularis oculi. Several techniques for facial nerve block can be used in conjunction with retrobulbar block.
See also
*
Eye surgery
References
* Cousins, MJ; Bridenbaugh, PO (1998). ''Neural Blockade in Clinical Anesthesia and Management of Pain.'' {{ISBN, 0-397-51159-0
* Anesthesiology Inf
AnesthesiologyInfo.com is for sale
Regional anesthesia
Eye procedures
Ophthalmic drug administration