Local And Regional Anesthesia in Ophthalmology and Ocular Trauma

Appropriate selection of local and regional anesthesia in ophthalmic surgery depends on the planned procedure, necessary duration, and patient characteristics. There is considerable redundancy of sensory innervation to the face, and therefore a combination of anesthetic techniques is often needed to achieve optimal results. This chapter will briefly review types of ocular anesthesia with a focus on periocular anatomy and targeted anesthesia. Topical Ocular Anesthesia Topical anesthesia is a relatively fast and simple technique that provides superficial anesthesia without the potential hazards of injections. Its use is limited to low complexity cases with adequate patient cooperation, as it does not provide complete akinesia or intraocular pressure control. Topical anesthesia may be achieved using eye drop applications (e.g., proparacaine hydrochloride 0.5%, tetracaine hydrochloride 0.5%), gel application (e.g., lidocaine hydrochloride 3.5% gel), or anesthetic-impregnated sponge application. Subconjunctival Anesthesia Subconjunctival injection of local anesthesia involves direct infiltration of anesthetic under the conjunctiva. This local infiltration technique may be used in a variety of procedures, including intravitreal injections, cataracts, glaucoma, and pterygium surgery. Following a drop of topical anesthetic, a small gauge needle (27 to 30G) is used to administer local anesthesia 5-8 mm from the limbus at either a superotemporal or inferotemporal site. The needle is placed in a bevel-down position to reduce the risk of inadvertent penetration of the globe. A cotton-tipped applicator may be utilized to spread the anesthetic. The injection results in reliable concentrations of local anesthetic and improves patient comfort for ocular procedures. Sub-Tenon Anesthesia Sub-Tenon anesthesia involves the injection of local anesthetic into the potential space between the Tenon capsule and the sclera. The inferonasal conjunctival fornix is the site most commonly utilized for injection to avoid encountering the insertion of the medial rectus or inferior oblique muscles. Anterior or posterior injection techniques may be used to accomplish sub-Tenon anesthesia. Anterior injections are performed superficially just beyond the equator using low volumes (3 to 5 ml) of anesthetic. In contrast, posterior injections provide more anesthetic into the posterior intra- and extraconal spaces; this allows for smaller volumes of anesthetic with a lower risk of chemosis. Intracameral Anesthesia During intraocular procedures, intracameral injection of local anesthesia involves the administration of a small volume of anesthesia (0.1-0.5 mL) into the anterior chamber. Common intracameral agents include preservative-free lidocaine hydrochloride 1% and bupivacaine hydrochloride 0.5%. These agents must be free of preservatives, such as benzalkonium chloride or other agents, which may cause toxic anterior segment syndrome. Likewise, bisulfites may carry similar issues with corneal endothelial toxicity, although diluted forms of less than 0.025% appear safe. However, not all medications are available in preservative and bisulfite-free form, and the surgeon must be aware of specific ingredients utilized in each product. Intracameral anesthesia is frequently combined with topical anesthetic agents and subconjunctival or sub-Tenon anesthetics as an effective and safe method to achieve analgesia in cataract surgery. Local and Regional Anesthesia Targeted anesthesia can be administered through direct local infiltration or a regional nerve blockade. Local tissue infiltration is technically straightforward and sufficient for the exploration and repair of small soft tissue injuries. In cases of larger complex injuries, a nerve block is a useful tool to provide anesthesia to a larger area with a smaller amount of anesthetic while minimizing tissue distortion.The disadvantages of regional nerve block include pain with injection, the need for patient cooperation, and the risks associated with the injection technique and medication. Injection of any substance carries a risk of an allergic reaction, overdose, medication-specific side effects, bleeding, infection, and tissue damage. The more proximal the local anesthesia is injected to the nerve root and other important anatomical structures, the higher the risk of significant adverse reaction.