In cases where vitreoretinal surgery is indicated, selection of the appropriate anesthetic agent is essential to both the patient and providing ophthalmology team. Ideally, the anesthetic agent should provide the patient with the most possible comfort that still allows the ophthalmologist to operate optimally. Local or general anesthesia can be used, and each of these has its advantages and disadvantages. This article will explore each type, the indications for the use of each type, and challenges they bring to the health care team.

LOCAL ANESTHETIC

The development of regional, or local, eye anesthesia has significantly transformed vitreoretinal surgery, enabling procedures to be performed safely and effectively while patients are awake.¹ Different types of local anesthetics can be used for retinal surgery, including regional blocks (sub-Tenon, peribulbar, and retrobulbar) and topical options. Regional blocks are used when both akinesia and analgesia are required.³

Sub-Tenon Block

A sub-Tenon block necessitates making an incision in the sclera,² followed by the passage of a curved cannula.³ Subsequently, a local anesthetic (typically a 1:1 mixture of 2% lidocaine and 0.5% bupivacaine) is then administered beneath Tenon’s fascia.³ Due to its improved safety, this method of anesthetic has become the preferred choice over other regional block techniques.⁴ Although typically used for cataract surgery, sub-Tenon block for posterior segment surgery was found to be equally effective and as comfortable as a retrobulbar block.⁵ Overall, sub-Tenon block is suitable for most vitreoretinal procedures, and other ocular surgeries. There are various techniques that can be performed to successfully administer a sub-Tenon block with a high degree of efficacy. The initial incision into sub-Tenon space should be followed only with blunt probing thereafter so as not to perforate the surrounding tissue.⁶ Additional tips to ensure high patient comfort and long-term effectiveness of the anesthetic include injecting in different directions while the syringe is in the desired location so the solution can spread easily and keeping the cannula tip tight against the sclera to ensure it does not pass too deep into the orbit.⁶ Among other associated complications, pain, subconjunctival hemorrhage, and chemosis are potential adverse effects of sub-Tenon blocks.^2,7 Although these risks are uncommon, they must be considered before choosing sub-Tenon block for anesthesia.

Peribulbar Block

Peribulbar blocks are known for their distinctive extraconal approach involving the lateral insertion of the needle alongside the eye, through which the solution is administered into the region surrounding the intraconal orbital compartment.⁸ Peribulbar blocks offer anesthetic effects similar to sub-Tenon injections³; however, their administration can bring a higher degree of distress to the patient, potentially reducing patient comfort.^2,9 This technique is suitable for vitreoretinal surgery³ and has many benefits for the patient as well as the health care team, including but not limited to greater postoperative pain relief, minimizing impact to the management of diabetes, quicker recovery, greater patient turnover, and a reduction in equipment needed.¹⁰

One study published in 2000 found that administration of solely peribulbar blocks prior to posterior-segment surgery offered analgesia in 85% of patients, whereas peribulbar blocks supplemented with sub-Tenon block provided 99% of patients with sufficient analgesia.¹¹ Therefore, a combination of techniques may be beneficial for sufficient anesthetic treatment.

When administering a peribulbar block, the mixture administered largely influences the degree of akinetic and analgesic effects. Adding adjuvant dexamethasone to bupivacaine was found to offer longer akinetic and analgesic effects, in addition to reducing inflammation.¹² More rapid onset of akinesia may also be achieved by the addition of 50 mg of magnesium sulfate, which was found to decrease the onset time of akinesia when added to a lidocaine-bupivacaine solution.¹³ Furthermore, peribulbar blocks consisting of ropivacaine were associated with lower rates of failure compared to those containing bupivacaine.¹⁴

The mixture of choice should be determined beforehand while taking into consideration the length and severity of surgery as well as patient-specific factors. The risks of peribulbar blocks, although rare, must also be considered. It is important to consider potential complications associated with peribulbar blocks, including perforation, acute ischemic optic neuropathy, central retinal artery occlusion, and brainstem anesthesia, among others.^15-16

Retrobulbar Block

Retrobulbar blocks offer the strongest akinesia of any regional block,³ and they are suitable for most types of ocular surgeries, including vitreoretinal and glaucoma surgery, but the discomfort patients experience from this injection may lead surgeons to use other anesthetic techniques. Additionally, the optic nerve is at risk of being injured due to the posterior location of the injection, and complications such as globe perforation and retrobulbar hemorrhage are risks that must be considered.¹⁷ Some suggestions for successful administration of retrobulbar blocks include (1) using a rounded needle, such as the Atkinson needle, because the rounded point and short bevel facilitate smooth entry with reduced trauma to nearby vessels; (2) facing the needle bevel up toward the globe, which reduces the risk of globe perforation; and (3) manual compression of the eye after injection, which may help spread the anesthesia after initial administration.¹⁸ Although rates of serious complications resulting from retrobulbar blocks are relatively low, some suggest this method should be replaced by peribulbar blocks because they are similar in effectiveness and carry less risk.¹⁹ Furthermore, topical anesthetics, which have emerged as a common form of anesthetic for ophthalmic conditions, have been found to be as safe and effective as retrobulbar blocks for retinal surgery.²⁰ This finding may further raise doubts about the ongoing use of retrobulbar blocks.

Topical Anesthetics

Topical anesthetics are now the most used form of ocular anesthesia,³ and although they are still suitable for vitreoretinal surgery, they may be more suitable for anterior-segment surgeries, because this provides anesthesia to the anterior sclera, conjunctiva, and cornea while leaving intraocular contents unaffected.¹⁸ Topical agents provide the benefits of quick recovery, easier administration, and avoidance of complications related to needles.²¹ Some disadvantages include the lack of akinesia, potential patient discomfort resulting from awareness, and pain with sudden changes in intraocular pressure.¹⁸ These agents are commonly composed of proparacaine hydrochloride 0.5% and tetracaine hydrochloride 1%,⁸ although 4% lidocaine solutions have been used for retinal surgery,²² perhaps due to the posterior nature of the retina and increased length of surgery. Although topical agents were found to be as safe and effective as retrobulbar blocks for posterior vitrectomy,²¹ these surgeries are often of short duration and without complications, which must be considered. When compared to regional blocks, there is no risk of globe perforation, retrobulbar hemorrhage, or prolonged postoperative akinesia.²¹

The success of retinal surgery under topical anesthesia depends on various factors, and selection of topical anesthetics is case specific. Important considerations include type and duration of the surgery, possible complications, and overall health of the patient. These factors play a crucial role in determining the effectiveness of the topical anesthesia for retinal surgery. Some tips to ensure proper administration of topical anesthetics is to ensure that (1) the agent enters the eye appropriately, because the drop may not enter the targeted area if not administered carefully; and (2) the bottle carrying the agent is not contaminated by touching the patient’s eye. With proper administration, the eye can be effectively prepared for surgery while maintaining sterile practices and reducing infection and postoperative complications.

GENERAL ANESTHETIC

General anesthesia is suitable for all vitreoretinal surgeries because it offers the strongest option of anesthetic, but it is commonly used for lengthy and complex surgical cases, as well as in patients with multiple underlying health conditions.²³ Additionally, general anesthesia may be preferred when a patient has only 1 functioning eye, because regional blocks can temporarily affect vision due to the impact on the optic nerve. There are various general anesthetics available, administered either through inhalation or intravenous routes.¹⁰ In the context of vitreoretinal surgery, the position of the eye undergoing the procedure is an important consideration. Some suggest a neutral gaze position to be optimal for retinal surgery, which may require specific anesthesia techniques.¹⁰ For instance, achieving this position may necessitate the use of muscle relaxants and mechanical ventilation.¹⁰ It is crucial to monitor neuromuscular transmission when muscle relaxants are administered to ensure the relaxation does not abruptly wear off. The selection of anesthesia agents necessitates a comprehensive understanding of the patient’s medical and surgical history,²⁴ because individuals with retinal conditions often have associated comorbidities. These patients may also have cardiac disease, hypertension, or diabetes mellitus, and they be on multiple medication therapies.¹⁰ When choosing general anesthesia, the patient’s underlying health conditions must be considered, ensuring that they can continue certain medications and effectively manage their chronic illnesses while also receiving surgical treatment of their eye.

CONCLUSION

Although topical anesthesia has become more popular for ophthalmic surgical cases, regional blocks remain safe and effective, and they continue to be used. General anesthetic remains a strong choice for long, complex cases. Within each type of anesthetic administration, there are various techniques that can be followed to ensure the solution is adequately administered to the desired location. A thorough understanding of the patient’s past medical history, the type and length of surgery, and any anticipated complications must be considered when selecting the anesthetic for retinal surgery.³ RP

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