Anesthesia for patients undergoing ophthalmic procedures should balance patient comfort with procedural safety for an optimal outcome. Most ophthalmologists strive to use the least invasive form of anesthesia to minimize potential anesthesia-related complications, while also hastening visual and functional recovery. Patients should be engaged in anesthetic considerations through the informed-consent process, and many patients now expect to be involved in planning. Glaucoma physicians now perform a broad array of procedures and therefore must tailor anesthesia appropriately. Anesthetic considerations will differ for traditional glaucoma procedures, which may be longer, have higher risk, and be more painful, compared to minimally invasive procedures, in which rapid visual recovery is desired. This article will provide an overview, procedure-wise, of various anesthetic considerations in glaucoma care.
Trabeculectomy
Trabeculectomy remains the gold standard glaucoma procedure to achieve a very low intraocular pressure (IOP). With this reward comes considerable intraoperative risk, making proper anesthesia crucial to success. Unfortunately, anesthesia itself can cause sight-threatening complications, especially in vulnerable glaucoma patients. These anesthetic risks must be weighed against the likelihood of developing further glaucomatous vision loss.
Local anesthetic, targeted posterior to the globe (retrobulbar, peribulbar, posterior sub-Tenon), is a common technique utilized in trabeculectomy. A retrobulbar block (RBB) provides the benefit of akinesia in addition to anesthesia, minimizing the risk of complications from intraoperative eye movement. Mild RBB-related proptosis may also improve exposure. Among the most dreaded complications of RBB is retrobulbar hemorrhage, which can raise intraorbital pressure, leading to optic-nerve ischemia.1,2 A peribulbar block (PBB) offers less risk of retrobulbar hemorrhage but may require a longer onset time or result in incomplete akinesia.1 In both RBB and PBB, the sheer volume of anesthetic injection can raise IOP and temporarily impair blood flow to the optic nerve, leading to optic nerve ischemia and “wipe-out” or “snuff” of the visual field in eyes at risk.3,4 Vision loss can also be caused by direct trauma to the optic nerve from the needle, needle-induced hematoma, or epinephrine use.5,6
A subtenon block (STB) allows for targeted delivery of anesthesia without the use of a sharp needle, while still providing eye immobility and analgesia.7 A comparison of the quality of analgesia among topical, retrobulbar, and subtenon techniques found that 99% of patients who received an STB had complete intraoperative analgesia compared to 83% with RBB and 69% with topical.8 An STB is associated with the same major complications seen with needle blocks, but the incidence is much lower.9-11 Indeed, needle blocks have a 2.5-fold increased risk of serious sight- and life-threatening complications.11 Notably, an STB, if allowed to reflux anteriorly, can cause conjunctival or tenon edema, making tissue manipulation more challenging.
Subconjunctival anesthetic, a less-conventional technique, allows for anesthesia without impacting eye movement, which can be used to the surgeon’s advantage.1,12 The absence of corneal traction reduces globe distortion, making it easier to obtain accurate tension when suturing. Additionally, subconjunctival anesthesia avoids the risks associated with posterior anesthesia because optic nerve blood flow is unaffected.3,4 Dietlein et al found that there were no significant perioperative and postoperative differences concerning IOP, filtration-bleb bleeding, hyphemia, hypotony, and choroidal detachment between patients who received trabeculectomy with general anesthesia and those receiving subconjunctival anesthesia.12 Compared with posterior needle blocks, subconjunctival injection may be less painful and may reduce the need for supplemental anesthesia during surgery.13 Subconjunctival anesthesia does require a certain degree of cooperation from the patient, who must be able to follow instructions, and an infraduct must be used to expose the surgical site. Hearing-impaired patients or patients or who speak a different language may still need a traction suture.
Pure topical anesthesia (TA) has the major benefit of rapid visual recovery, which is a nice option for patients with low vision in the nonoperative eye. Zabriskie et al performed a prospective, randomized study comparing topical bupivacaine to RBB for trabeculectomy and found that pain was equally minimal in both study groups. TA involves no risk of retrobulbar hemorrhage, artery occlusion, or optic nerve or globe injury compared to posterior needle blocks.14 Possible disadvantages of TA include blepharospasm, lack of ,akinesia and possible patient discomfort, all of which can interfere with surgery.2,14,15 Ocular motility withstanding, both topical and subconjunctival techniques require considerable surgeon efficiency and skill.
Glaucoma Drainage Implants
Glaucoma drainage implants (GDIs) require more posterior dissection than other glaucoma procedures and often require manipulation of the extraocular muscles. Tube shunts are also a dependable procedure for surgically complex eyes, which may be more difficult to anesthetize due to inflammation or scarring. Adequate access and therefore globe manipulation for GDI are crucial, especially for surgeons operating without a skilled assistant.
RBB is effective in GDI to achieve adequate anesthesia and akinesia. Again, proptosis from a posterior block can also be used to the surgeon’s advantage. Theventhiran et al compared RBB to TA (tetracaine) with subconjunctival lidocaine in patients undergoing glaucoma filtering surgeries, including Ahmed glaucoma implants (AGI), Baerveldt glaucoma implants, and trabeculectomy.16 Tetracaine was associated with a slightly higher average postoperative pain score and greater need for intraoperative intravenous anesthesia compared to RBB, but the overall severity of pain was mild for both groups. The type of glaucoma procedure or length of procedure had no impact on patients’ perceptions of pain. Rebolleda et al randomized patients undergoing AGI to topical lidocaine 2% gel or RBB and found no significant difference in patient-reported pain intraoperatively or postoperatively.17 Patient cooperation was similar for both groups, but duration of surgery was longer in the TA group. No intravenous anesthetic was utilized at any point.
Overall, the feasibility of TA may depend on the type of TA used, patient selection, surgeon technique, and supplementation with intravenous anesthetic and/or subconjunctival anesthesia. Hence, creative anesthetic combinations should also be considered. Combined anterior subtenon, topical, and intracameral, also known as “blitz,” anesthesia has been studied as an effective option for trabeculectomy, phacotrabeculectomy, or GDI. Compared to RBB, no statistically significant difference was found in the mean intraoperative or postoperative pain scores.18
Cyclophotocoagulation
Cyclophotocoagulation (CPC) is an effective treatment for medically resistant glaucoma. It is often performed with RBB/PBB due to the degree of pain associated with the procedure. Posterior blocks have the added benefit of akinesia, a desirable effect when precisely targeting laser delivery. Posterior blocks also help with early postoperative pain, potentially reducing the need for opioids, but postoperative patching can lead to functional challenges, especially if the contralateral eye is visually impaired.
A survey of UK ophthalmologists found that 50% preferred STB, 46% PBB, 13% RBB, 4% topical, 2% subconjunctival, and 31% general anesthetic for CPC (respondents were allowed more than 1 option as their preferred anesthetic choice).19 A prospective assessment of patient satisfaction comparing STB and PBB for CPC found that both modalities provided adequate analgesia, with PBB providing slightly lower pain scores compared to STB.20
Because RBB and PBB may raise IOP and consequently compromise optic nerve function, other options may need to be utilized in certain cases. Subconjunctival anesthesia can provide effective pain control while substantially reducing the risks associated with RBB and PBB.21 However, a significant delay between administration and CPC application is necessary. Notably, a subconjunctival hemorrhage caused by a subconjunctival injection may impede proper energy delivery to the ciliary body and can lead to conjunctival burns.22
Minimally Invasive Glaucoma Surgeries
Minimally invasive glaucoma surgeries (MIGS) share 5 preferable qualities: an ab-interno approach, a minimally traumatic procedure, IOP-lowering efficacy, a high safety profile, and a rapid recovery with minimal impact on quality of life.23 Because MIGS aim to cause minimal disruption to lifestyle and vision, anesthesia choice should align with the procedure. Typically, topical/intracameral anesthesia is adequate. Nevertheless, surgeons should have a low threshold to use RBB or PBB in the uncooperative patient because angle-based MIGS leave little room for error. Unexpected ocular movement can result in severe complications. Akinesia is particularly helpful when learning intraoperative gonioscopy or MIGS. Anecdotally, patients may experience more discomfort with 360 cannulation procedures (canaloplasty, viscodilation, GATT), so posterior blocks should be considered. It is important to note, however, that an akinetic eye may rest in exotropia, rendering gonioscopy and en-face angle viewing more challenging.
Xen (Allergan), a MIGS device designed for ab-interno subconjunctival placement, can be implanted with topical/intracameral anesthesia. However, off-label open-conjunctival modifications that require cautery may require more anesthesia. Subconjunctival anesthetic can be mixed with a subconjunctival mitomycin C injection, as utilized in trabeculectomy.24 Alternatively, a short-acting PBB or STB placed inferotemporally allows for adequate anesthesia and rapid postoperative recovery. Any subconjunctival chemosis or bleeding related to the block remains away from the typical superonasal or superior surgical site.
Conclusion
Appropriate anesthesia is crucial to ensure patient comfort and an optimal surgical outcome. Glaucomatous eyes are at heightened risk for optic nerve damage from local anesthesia, and needle blocks in particular carry a low but serious risk of complications, including wipe-out of vision. Nevertheless, most glaucoma surgery is performed on the anterior aspect of the eye and can be safely performed using any of the aforementioned anesthesia techniques. Ultimately, surgeon comfort level, experience, and individual patient factors, including ocular and systemic comorbidities, bleeding risk, and cooperation, all play roles in the complex decision making that occurs with anesthesia selection.
References
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- Gross A, Cestari DM. Optic neuropathy following retrobulbar injection: a review. Semin Ophthalmol. 2014;29(5-6):434-439. doi:10.3109/08820538.2014.959191
- Hulbert MFG, Yang YC, Pennefather PM, Moore JK. Pulsatile ocular blood flow and intraocular pressure during retrobulbar injection of lignocaine: influence of additives. J Glaucoma. 1998;7(6):413-416.
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- Theventhiran A, Shabsigh M, De Moraes CG, et al. A comparison of retrobulbar versus topical anesthesia in trabeculectomy and aqueous shunt surgery. J Glaucoma. 2018;27(1):28-32. doi:10.1097/IJG.0000000000000834
- Rebolleda G, Muñoz-Negrete FJ, Benatar J, Corcostegui J, Alonso N. Comparison of lidocaine 2% gel versus retrobulbar anaesthesia for implantation of Ahmed glaucoma drainage. Acta Ophthalmol Scand. 2005;83(2):201-205. doi:10.1111/j.1600-0420.2005.00420.x
- Kansal S, Moster MR, Gomes MC, Schmidt CM, Wilson RP. Patient comfort with combined anterior sub-Tenon’s, topical, and intracameral anesthesia versus retrobulbar anesthesia in trabeculectomy, phacotrabeculectomy, and aqueous shunt surgery. Ophthalmic Surg Lasers. 2002;33(6):456-462.
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- Lim MC, Hom B, Watnik MR, et al. A comparison of trabeculectomy surgery outcomes with mitomycin-c applied by intra-tenon injection versus sponge. Am J Ophthalmol. 2020;216:243-256. doi:10.1016/j.ajo.2020.03.002