Ophthalmic surgery is one of the most common procedures that require anesthesia. Options include local anesthetic options such as topical, sub-Tenon’s, peribulbar and retrobulbar techniques as well as general anesthesia.
Local ocular anesthesia is indicated in that subset of ophthalmologic surgeries in which general anesthesia is not needed, and particularly for those surgeries requiring patient cooperation. The subset of surgeries appropriate for regional ocular anesthetic includes nearly all intraocular surgeries, including for example cataract removal, corneal transplantation, glaucoma surgeries, vitreoretinal surgeries, scleral buckling, strabismus repair, and enucleation.
Long eye (in the anterior to posterior axis, evidenced by high myopia), staphyloma (abnormal protrusion at a weak spot in the wall of the eye), enophthalmos (posteriorly or deep set eyes), and extended surgery duration are relative contraindications to retrobulbar and peribulbar anesthesia. In an uncooperative patient, patients deemed to be unable to follow commands during surgery, children and those with uncontrollable neurological movements, general anesthesia may be considered.
Patient education about what to expect prior to surgery is important to reduce anxiety and increase compliance.
Specifically ask about bleeding disorders, and anti-coagulant or anti-platelet drugs. Note that patients receiving anti-coagulants may continue medications as long as levels are within therapeutic ranges, whereas there is no current recommendation for patients on anti-platelet agents. An axial length measurement of the eye may be useful if considering a retrobulbar block, for the increased risk of globe or optic nerve damage in long eyes.
Avoidance of wrong site surgery
On the day of surgery the operative eye is marked in a standardized, unambiguous manner to avoid wrong-site surgery.
- Any anesthesia method will require topical anesthetic and antiseptic. Particular anesthetic modalities also require:
- Sub Tenon’s: Westcott scissors, blunt curved cannula
- Retrobulbar: syringe and 32mm needle
- Peribulbar: syringe, 25mm needle
- Additionally, particular materials and tools needed for surgery should also be available.
- Cocaine was the first anesthetic used for ocular anesthesia by Knapp in 1884. Currently, a combination of lidocaine and bupivacaine is reported to be the most popular, as the short acting lidocaine provides immediate anesthesia while bupivacaine provides longer duration of anesthesia.
- Hyaluronidase promotes anesthetic diffusion and has been demonstrated to cause more rapid and complete anesthesia than injections lacking hyaluronidase.
- Epinephrine is used to increase intensity of anesthesia, minimize bleeding, and slow systemic uptake. However, because epinephrine may cause retinal ischemia through constriction of the ophthalmic artery, its use is usually avoided in patients with underlying cerebrovascular disease.
- Sodium bicarbonate increases the pH of the anesthetic solution, shifting the anesthetic agent bupivacaine to its noncationic form that more readily diffuses into surrounding nerves.
There are few randomized controlled trials to compare the different types of regional anesthesia, and against general anesthesia in the areas of efficacy and safety. In a survey based study done in the UK, Eke confirmed that adverse events in regional ocular anesthesia are rare, but can occur with all types of regional anesthesia.
Topical anesthetic, with the use of supplemental intracameral lidocaine, is the most commonly used method of anesthesia for cataract surgery in the US. The upsides of this technique are that it does not alter vision, avoids the use of needles, and may not require sedation. The downside is that it does not provide akinesia, in that the eye is still under voluntary movement. Therefore, careful patient selection for this technique is paramount.
First the eye is numbed with a topical anesthetic such as proparacaine 0.5%, then an antiseptic such as 10% povidone-iodine is applied to the skin of the lower eyelid. The patient may be lightly sedated but ideally is still able to respond to commands. A needle no more than 32mm is then inserted bevel up into the lower eyelid just above the orbital rim at the border between the lateral and middle third of the lower eyelid. Alternatively, the needle can be inserted directly into the conjunctiva, bypassing the lid entirely, which may be associated with a lower risk of lid ecchymosis. Other authors recommend needle placement as far lateral as possible, below the lateral rectus, or even upward displacement of the eyeball with one hand while advancing the needle. The globe is watched for any movement during needle insertion, as this could indicate that the needle has contacted the sclera and puts one at risk of puncturing the globe. The needle is inserted while held horizontally until the tip is judged to be posterior to the inferior-most part of the globe, at which time the needle tip is angled superiorly 45˚ and slightly medially. After withdrawing the syringe to ensure no blood return, the anesthetic can be slowly dispensed into the retrobulbar space, usually at a volume near 5mL.
A note on needle position and delicate structures: the retrobulbar block (and peribulbar for that matter) has been decreasing in use in recent years in favor of non-needle based techniques. Factors that predispose to globe penetration include a long eye (in the anterior to posterior axis, evidenced by high myopia), staphyloma, enophthalmos, an uncooperative patient, and the use of a longer needle than needed. The classic Atkinson position, in which the gaze is directed upward and inward, is associated with complications and places the optic nerve, ophthalmic artery, superior ophthalmic vein, and posterior globe within striking distance of a 35mm needle and thus is no longer recommended.
The peribulbar block requires the same preparation as the retrobulbar, including conscious sedation of the patient, local anesthesia, and antiseptic. The needle, however, is usually shorter than 25mm, and is advanced horizontally under the globe without the upward advancement. The presumed further distance from the nerve sheath is made up for by injecting a larger volume of anesthetic, commonly 6-10mL. The lower chance of globe penetration should be weighed against the greater volume of anesthetic required in peribulbar blocks, theoretically increasing the risk of brainstem anesthesia. Edge found ocular injury rates of 0.007% for retrobulbar and 0.022% for peribulbar blocks. The only identifiable risk factor in all cases was posterior staphyloma, suggesting that staphyloma, and not simple axial elongation, may be the crucial factor.
As the name implies, this block is applied under Tenon’s capsule, the sheath that surrounds the eye from the optic nerve to the limbus and creates a potential space around the sclera, called the episcleral space. This block requires an incision to be made in the infero-nasal quadrant of the sclera, through which is passed a blunt, curved cannula to deliver 3-5mL of anesthetic into the episcleral space. If the larger 5mL volume is used, this will spread to the extraocular muscles and cause akinesia. Uptake of the sub-tenon’s technique may be slowed by some perceived downsides, despite evidence that it is safe and efficient. Perceived downsides include association with subconjunctival hemorrhage, a postoperative side effect that is transient and cosmetic, in addition to requiring the use of surgical tools that may not be readily available in outpatient day surgery locations.
This modality is usually reserved for patients that are unable to cooperate or communicate during surgery. Note that presence of intraocular gas, whether from penetrating trauma or therapeutic intervention, has been associated with vision loss in patients undergoing general anesthesia with nitrous oxide.
Perioperative complications and management
- Transient decrease in visual acuity: decreased vision after administration of local anesthetic, likely due to conduction blockade of the optic nerve or ischemia related to optic nerve compression. Patients should be warned about the possibility beforehand to minimize anxiety during the surgery.
- Permanent vision complications: result of penetration of the globe, optic nerve, or central retinal artery. Trauma to the nerve is most associated with the Atkinson position.
- Brainstem anesthesia: symptoms of difficulty breathing, dysphasia, hypertension, tachycardia, severe shivering, agitation, confusion, or unconsciousness generally occurring within a few minutes of anesthetic administration. Supportive treatment is essential, including interventions to support respiration and stabilize blood pressure. Mechanism may be from spread through the optic nerve sheath or foramina of the orbit.
- Diplopia due to extraocular muscle injury: generally due to injection of anesthetic into a muscle sheath.
- Oculocardiac reflex: rare during eye surgeries with regional anesthesia, but as common as 50-80% in ocular surgeries with general anesthesia. Manipulation of the extraocular muscles or conjunctiva, or pressure on the globe, can trigger cardiac arrhythmias and hypotension. Efficacy of prophylaxis with anticholinergics such as atropine or glycopyrrolate is not consistently demonstrated.
- Retrobulbar hemorrhage: may be arterial or venous. Arterial tends to expand quickly and cause rapid orbital swelling and increased IOP, thus IOP should be monitored in the event of rapid hemorrhage. If pressure is substantially increased, particularly in conjunction with paleness of the optic nerve on fundoscopic exam, steps should be taken to reduce pressure within the orbit including a canthotomy.
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