Regional anesthesia is used in those procedures in which one desires to obtain akinesia of the globe, as well as sensitivity block. The types of regional anesthesia are retrobulbar, peribulbar, and subtenon. Retrobulbar anesthesia is a type of regional anesthetic nerve block in the retrobulbar space, located behind the globe of the eye.
The technique was first described in 1884 by Herman Knapp. The main goal of this procedure is to obtain anesthesia of the cornea, uvea, and conjunctiva, as well as akinesia of the extraocular muscles by blocking the ciliary nerves and the II, III, VI cranial nerves, which all go through the intraconal space.
- Intraocular procedures (cataract surgery, vitrectomy, tube shunt placement, etc)
- Cyclodestructive procedures
- Corneal procedures
- Strabismus surgery
- Enucleation and evisceration
- Hypersensitivity or allergy to local anesthetic agents
- Active orbital infection
- Increased axial length of the globe
- Bleeding diathesis
- Anticoagulant use
- Thyroid associated orbitopathy
- Space occupying orbit lesion
- Previous scleral buckling
- IV sedation
- Atkinson or retrobulbar needle (23- or 25-gauge and 1.5 inches (38 mm) in length)
- 5 or 10mL syringe
- Povidone-iodine (5% ophthalmic)
- Anesthetic agent
- Gauze package
- Honan ballon
Intravenous sedation is commonly used to improve patient cooperation, to provide analgesia, and obtain amnesia for the procedure. Short acting agents are often used. Ocular surface may be topically anesthetized prior to the procedure. Vital sign monitoring, including cardiac and respiratory are used. Supplemental oxygen is commonly provided. Positioning of the patient is preferred in supine position with head resting on a flat surface. Depending on location of performed procedure, type of procedure and patient cormorbidities, involvement of an anesthesia team may be critical.
Choice of the anesthetic agent depends on the duration of the surgery to be performed. A single agent may be chosen or a combination of agents may be used. The most used combination is the Lidocaine 2% with bupivacaine 0.75%. In general the use of epinephrine or other vasoconstrictors is avoided to prevent ciliary or ophthalmic artery spasm and permanent vision loss, except in cases of enucleation or evisceration. Hyaluronidase is used as an adjuvant by some physicians to improve spread of the anesthetics at 50 IU per mL.
- After appropriate patient preparation, monitoring and positioning, Patient must be facing straight in primary gaze position.
- Inferior lid is then prepared with alcohol swab or povidone-iodine. The inferior orbital rim should be located and palpated while the globe is mildly pushed to elevate and clear the path for the needle insertion. Generally the injection point is approximately 1/3 from the lateral canthus.
- Bevel of the needle should face upward towards the globe to avoid perforation of the globe.
- Needle is inserted perpendicular through the inferior eyelid at the superior edge of the inferior orbital rim in the saggital plane of the temporal limbus to avoid major vessels and decrease the risk of a retrobulbar hemorrhage. The needle is advanced parallel to the orbital floor with an inclination of 10 to 15 degrees. Approximately 1 cm after penetrating the orbital septum, posterior to the equator often felt as a "pop", the needle is redirected 30 to 45 degrees superonasal and advanced 2.5 to 3.5 cm until the intraconal space.
- Once inside the intraconal space, gently move the needle and beware of any resistance or significant rotation of the globe to assure no perforation of the globe has occurred.
- Aspirate syringe to ensure no blood return and confirm no vessels compromise.
- Slowly inject 3 to 4 ml of anesthetic and remove needle.
- With the eye closed apply resistance to the volume injected apply pressure with gauzes or (historically) a Honan balloon at 20 to 30 mmHg for 5 minutes to prevent a hemorrhage and increase diffusion of the anesthetic agent. Monitor for retrobulbar hemorrhage.
- Assess the degree of akinesia and anesthesia 5 minutes after the injection.
Complications from retrobulbar block occur in 1-3%, ranging from mild to severe. The following are the complications described in literature:
- Retrobulbar hemorrhage
- Ocular perforation
- Subarachnoid or intradural injection
- Diplopia secondary to miotoxicity
- Cardiorespiratory distress
- Contusion and atrophy of the optic nerve
- Vascular retinal occlusion
- Corneal abrasion
Perforation (needle in eyeball) can cause blindness, but is rare. Mechanisms include choroidal hemorrhage, retinal detachment, vitreous hemorrhage, or needle trauma to retina/nerve and associated scarring. If anesthetic is injected into the eyeball, this can cause a scleral rupture (ocular explosion). Needle damage is more likely with longer needles, bigger eyes (myopic eye with long axial length) and eyes with posterior or lateral staphyloma (this is common in highly myopic eyes). Eyes that are deep-set in the orbit, or in small orbits, are also at higher risk. An alternative technique is peribulbar anesthesia, which was previously thought to be lower-risk for perforation. However, both techniques have a similar risk of globe perforation. To avoid this risk, many practitioners use 'no-needle' sub-Tenon's anesthesia using a blunt-ended cannula, or topical/intracameral anesthesia.
Orbital hemorrhage may also cause blindness, if not recognize and treated rapidly and occurs in 0.04-1.7% of retrobulbar blocks. This can occur from venous or arterial source and will usually present with rapid-onset proptosis and a tense orbit, usually with obvious arterial blood in the orbit and/or subconjunctivally. Urgent decompression of the orbit with lateral canthotomy/cantholysis may be required. A good article describing how to decompress an orbit is freely available here. In addition, the EyeWiki article on orbital compartment syndrome describes how to perform a lateral canthotomy/cantholysis here.
Deaths can occur as a result of retrobulbar or peribulbar injections of local anaesthetic. If the needle inadvertenly punctures the optic nerve, anesthetic may be injected into the subarachnoid space and will track back to the brainstem. This may present as gradual-onset or sudden-onset alteration of consciousness (e.g. coma, with tonic-clonic seizures), apnoea, and unstable blood pressure. Practitioners should be aware of this possibility: resuscitation equipment should be available, staff should have resuscitation training, and there should be an agreed pathway to get the patient to an intensive therapy unit. With appropriate timely management and supportive therapy, a patient with brainstem anesthesia would be expected to make a full recovery. For further advice, see the UK Guideline
A Guideline discussing all aspects of safer practice of regional anesthesia in ophthalmology has been published in the UK.
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