LA agents

New anesthetic agents have shown little advantage over established agents. Lidocaine continues to be popular for LA cataract surgery because of rapid onset, low toxicity, and suitable duration of effect. Bupivacaine may be myotoxic to extraocular muscles. Hyaluronidase speeds the diffusion of injectate through tissues, and may improve quality of LA blocks. Severe orbital inflammation has been described with animal-derived hyaluronidase, including some cases of blindness. In recent years, hyaluronidase from a recombinant DNA source has become commercially available, hopefully with an improved safety profile. Topical anesthetic eye-drops include lidocaine, proxymetacaine (less stinging, probably weaker anesthetic effect), and tetracaine (probably stronger anesthetic effect).

Sharp needle blocks

Retrobulbar and peribulbar LA injections1 (Figs 10.1, 10.2) give excellent akinesia and analgesia, although they are associated with sight-threatening and life-threatening complications. The needle may penetrate the globe or optic nerve, and this can result in blindness. Long myopic eyes, particularly those with a staphyloma, are at particular risk of this complication. If the needle penetrates the meninges around the optic nerve, the LA may enter the subdural space and track back to the brainstem; brainstem anesthesia may present with apnea, fitting, unstable blood pressure, and possibly death1,6. While these complications are rare, they are of course devastating. Therefore, it is recommended that these techniques are only used after suitable training, consideration of the anatomy and eyeball size/shape for each case, and with back-up available in case of an inadvertent brainstem injection1,4,5. Even in the best hands, these complications can occur with sharp needle blocks1. The advent of small-incision phacoemulsification was associated with renewed interest in LA techniques which should have a fewer complications.

Fig. 10.1 Retrobulbar anesthesia.

A sharp needle injects anesthetic behind the globe, within the cone formed by the extraocular muscles.

From Rubin A, Techniques in Regional Anesthesia & Pain Management 2000;4(1):45–50.

Fig. 10.2 Peribulbar anesthesia.

Sharp needle introduced, outside the muscle cone.

From Rubin A, Techniques in Regional Anesthesia & Pain Management 2000;4(1):45–50.

SubTenon’s anesthesia

The SubTenon’s LA technique2 involves passing a blunt-ended cannula between Tenon’s capsule and the sclera. If the cannula is blunt enough, there should be no risk of penetrating the globe or optic nerve (Fig. 10.3). The anatomical connection between the sclera and dura means that the LA should not be able to reach the brainstem. Thus, the technique should be safer than sharp needle blocks.

Fig. 10.3 SubTenon’s anesthesia.

A blunt cannula introduces the anesthetic between Tenon’s capsule and sclera.

Numerous variants of the STA technique have been described2. Common techniques include (i) posterior injection using a long metal subTenon’s cannula, (ii) anterior injection using a short plastic subTenon’s cannula, and (iii) posterior injection using a flexible intravenous cannula. Anterior injections are more likely to cause chemosis or subconjunctival hemorrhage. Larger volumes of injectate give better akinesia, and hyaluronidase can aid diffusion.

Complications of subTenon’s anesthesia do appear to be rarer, and less severe, than with sharp needle blocks2,6. Chemosis and subconjunctival hemorrhage are very common. Orbital hemorrhage occurs rarely, generally due to damage to a vortex vein. A scarred conjunctiva (e.g. from previous cryo/explant surgery) can make the initial dissection difficult or impossible. Posterior injections have rarely been associated with optic nerve infarcts, episodes suggestive of brainstem anesthesia, and even death2. It is possible that these reports are indeed true complications, perhaps due to anatomical variants at the optic nerve/scleral junction which may render some patients particularly susceptible. Because of these concerns, some authors have cautioned against using subTenon’s injections that are very posterior, particularly if a metal cannula is used.

Topical and topical-intracameral LA

Topical anesthesia is becoming increasingly popular for phacoemulsification. It has the advantage that virtually no training is required, no additional personnel or time is needed for the anesthetic, and patient satisfaction rates are high. Some surgeons use purely topical anesthesia (e.g. tetracaine 1% drops). Many will routinely supplement topical anesthesia with an intracameral dose of non-preserved anesthetic. A recent meta-analysis concluded that intracameral lidocaine does improve patient comfort, with no evidence of corneal toxicity or other adverse events3. Many surgeons feel that intracameral LA is important for patient comfort, particularly if the instruments inadvertently touch the iris.

A standard technique for topical-intracameral LA is as follows: (i) The patient is counselled about their surgery, and warned that they may be aware of some sensation but they should not expect any pain. The patient is advised to look toward the microscope light throughout the procedure, and warned that they may experience some unusual visual sensations such as alterations in light intensity, swirling lights, or loss of light perception during surgery. Proxymetacaine is instilled, and may be followed by tetracaine 1% drops. (ii) After the initial corneal incision, non-preserved lidocaine 1% or 0.5% is injected into the anterior chamber, using a 1–2 ml syringe and intraocular cannula. The patient should be warned that this may sting slightly. (iii) Surgery then proceeds as normal, and the patient is reminded to keep looking toward the microscope light. If the patient initially finds the light too bright, then the light should be reduced to low intensity, then slowly brightened – this can usually be done gradually and does not delay the surgery. This technique is equally suitable for more complex surgery including pupil stretch, iris hooks, anterior vitrectomy, and sulcus-postioned lens implants.

Variants of this technique have been described, including the use of lidocaine or tetracaine gel for topical anesthesia, and a viscoelastic that includes lidocaine for intracameral use. With topical gel techniques, it is important to instill povidone-iodine before, not after, the gel.

It has been suggested that topical/intracameral LA may give an increased risk of surgical complications, because of a potentially mobile eye. However, many believe that the opposite is true. By fixating on the light, the patient keeps their eye perpendicular to the microscope, thus facilitating surgery. If an LA block is used, then the akinetic eye may make it difficult to position the patient with the eye ‘on axis’. Furthermore, the volume of LA behind the eye may increase vitreous bulge. At this author’s institution, topical/intracameral LA without sedation is used for over 98% of all cataract surgery (including for teaching trainees), and the rate of surgical complications is reassuringly low8.

LA cataract surgery in upright position

Some patients cannot position with their head horizontal for cataract surgery, because of medical problems such as ankylosing spondylitis or severe Meniere’s disease. They may be high risk for GA, but surgery can take place with the patient seated upright, using topical-intracameral LA9. The operating microscope is rotated toward the horizontal, and the surgeon sits or stands, facing the patient. An inferiorly placed incision is used. Topical-intracameral LA is particularly advantageous for these patients, because the patient will be able to keep the eye in line with the microscope. It is important to ensure that both patient and surgeon are happy with positioning before surgery commences.

Intracameral LA to dilate the pupil

Following the observation that intracameral LA will dilate the pupil, some surgeons have tried using intracameral lidocaine instead of preoperative dilating drops. However, the degree of pupil dilatation may be insufficient for safe surgery, particularly for some patient groups such as those with glaucoma. Some have reported success with an intracameral ‘dilating mixture’ comprising lidocaine and mydriatics.