Anesthesia for Cataract Surgery

• Local and topical techniques are now the norm

• 2% of patients requiring general anesthesia

Local Anesthesia

• Minimal disruption for the patient• Sedation may be useful (Standard fasting

times)• Monitoring: ECG, pulse oximetry• Supplemental oxygen

Local Anesthesia

• Topical anesthesia• Retrobulbar block• Peribulbar block• Sub-Tenon's block

Topical anesthesia

• Oxybuprocaine (benoxinate) 0.4% : frequently used

• Proparacaine (proxymetacaine) 0.5% is less toxic to the corneal epithelium, shorter duration of action (20 min)

• Other: including tetracaine (amethocaine) 0.5–1%, lidocaine 1–4% and bupivacaine 0.5–0.75%, longer duration, but increased associated corneal toxicity

Advantages•No risk associated with needle insertion•Reduced risk of periocular hemorrhage•Functional vision is maintained; advantageous for uniocular patients•Reduced postoperative diplopia and ptosisDisadvantages•An awake and talkative patient can be distracting for the surgeon•No akinesia of the eye•Less-effective anesthesia than sub-Tenon's block•Increased risk of surgical complications. If difficulties or problems

occur anesthesia may be inadequate•May be unsuitable for less-experienced surgeons

Adverse Effects of Topical Ocular Anesthetics•Direct corneal effects – alteration of lacrimation and tear film stability•Epithelial toxicity – healing has been shown to be delayed when an

epithelial defect occurs (lidocaine does not appear to affect healing)•Endothelial toxicity – this occurs when penetrating trauma is present

and appears to be related to the preservative benzalkonium•Systemic effects – lethal toxicity (this is only a problem with cocaine)•Allergy and idiosyncratic reactionsSecondary Adverse Effects•Surface keratopathy

• Topical anesthesia may be combined with subconjunctival or, more commonly, intracameral anesthesia to improve patient comfort

• As visual perception is not lost• Several studies showing inferior analgesia

compared to both peribulbar and sub-Tenon's blocks, and an increase in surgical complication rate

Retrobulbar Block

• Aim is to block the oculomotor nerves before they enter the four rectus muscles by depositing local anesthetic directly into the posterior intraconal space

• Peribulbar block offers a safer

Advantages•Reliable akinesia•Onset of block is quicker than with peribulbar anesthesia•Low volumes of anesthetic result in a lower intraorbital

tension and less chemosis than with peribulbar blocks•Temporary loss of visual acuity occurs more reliably than for

peribulbar blockDisadvantages•Risk of brainstem anesthesia – reason for the development of

the peri bulbar block•Risk of myotoxicity and globe perforation

• Clean the lower lid with the prep wipe.• Ask an assistant to pull the upper lid upward to see if the block needle is going

through muscle, which will be indicated by movement of the globe.• Palpate the inferior orbital margin. Feel the infraorbital notch, approximately at

the junction between the medial two thirds and the lateral one third of the inferior orbital rim.

• Make a skin wheal immediately lateral to the notch using a small gauge (30 gauge) needle and syringe.

• Advance the block needle straight down and perpendicular to the plane of the face, until you encounter a distinct pop that indicates passage through the orbital septum

• Angle the block needle 45 degrees medially and 45 degrees superiorly toward the apex of the orbit until the second pop through the muscle cone is felt

• Aspirate for blood.• Inject 2 to 3 mL of the anesthetic solution.

Peribulbar Block

• instill local anesthetic outside the posterior muscle cone

• avoid accidental injection into the optic nerve

Technique

• local anesthetic drops are applied to the cornea• At the inferotemporal lower orbital margin a 25-

gauge, 25 mm needle is advanced parallel to the plane of the orbital floor either trans cutaneously or transconjunctivally

• A degree of upwards and inwards angulation may be needed once past the equator of the globe

• Local anesthetic (4–6 mL) is injected at a depth of about 20 mm from the inferior orbital rim

Complications-Most serious complications of peribulbar

anesthesia relate to the use of sharp needles.•Globe perforation/penetration•Retrobulbar hemorrhage•Extraocular myotoxicity

Sub-Tenon's Block

• Tenon's capsule is a facial sheath, a thin membrane enveloping the eyeball and separating it from orbital fat

Technique

• The conjunctiva is anesthetized first with a topical local anesthetic of choice

• The commonest approach is via the infranasal quadrant• The eye is cleaned with iodine 5% and the patient asked to

look upwards and outwards• Aseptically, the conjunctiva and Tenon's capsule are held 3–

5 mm from the limbus using non-toothed Moorfields forceps• A small incision is made through these layers using blunt-

tipped, sprung Westcott scissors exposing the sclera• A cannula is then advanced into the sub-Tenon space and

around the globe

General Anesthesia

• unsuitable for local anesthesia• method of choice for babies, children, and the

uncooperative

Advantages•Patient comfort•Ideal operating conditions – a quiet, immobile patient and soft eye•Allows for rapid alterations in intraocular pressure if required•No risk of complications associated with local anesthetic blocks•No residual paralysis of the eye when the patient is awake•Bilateral surgery can be performed•Better conditions for teachingDisadvantages•Slower turnaround times•More expensive•Greater risk in frail elderly•Greater physiological disruption for patient

• Ophthalmology , Fourth Edition, Myron Yanoff, and Jay S. Duker