FRCA Notes

Regional Anaesthesia for Ophthalmic Surgery

Resources

  • Regional blocks provide superior analgesia to topical techniques, as well as providing a degree of akinesis
  • They do, however, carry the risk of sight- or even life-threatening complications

  • As with the performance of any regional technique, the patient should be AAGBI-monitored with cannula in situ, and have appropriate resuscitation equipment nearby to ward off evil spirits

Absolute Relative
Patient refusal Inability to lie still
True local anaesthetic allergy Poor compliance e.g. confusion, communication difficulties
Localised sepsis Grossly abnormal coagulation
Perforated globe or penetrating eye injury
Procedure >90mins duration


  • Regional techniques can be broadly split into 'blunt cannula' and 'sharp needle' techniques

  • The sub-Tenon's block is the blunt cannula technique of choice

  • There are a few sharp needle blocks to be aware of:
    • Peribulbar block (i.e. extraconal block)
    • Modified retrobulbar block (i.e. intraconal block)
    • The traditional retrobulbar block, which is now effectively obsolete

  • Amide local anaesthetics are most frequently used in regional eye blocks, either:
    • 2% lidocaine
    • 0.5% levobupivacaine
    • Or a mixture of the two

Additions

  • Hyaluronidase facilitates local anaesthetic spread thus improving block efficacy; the optimum dose is debated
  • Adrenaline, at a concentration of 1:200,000, prolongs the block duration

  • Tenon's capsule arises at the peri-limbal sclera anteriorly and inserts into the fibres of the optic nerve dural sheath posteriorly
  • The sub-Tenon's block aims to deposit local anaesthetic within the sub-Tenon's (episcleral) space to block the long and short ciliary nerves, and ciliary ganglion
  • On account of using a blunt cannula, it benefits from a 2.5x decrease in complications compared to sharp needle blocks
    • This makes it safe for use in those with an axial length >26mm

  • The elderly tend to have thinner Tenon's capsules, making the block easier
  • Younger individuals, or those who've had previous surgery, may have thicker and/or scarred Tenon's which can make the block harder

Conduct

  • Both topical anaesthetic drops and aqueous iodine are applied to the conjunctiva to provide analgesia and sterility
  • A Barraquer speculum is inserted to hold the eyelid open
  • The patient is instructed to look up and out

  • Non-toothed forceps are used to take a bite of conjunctiva + Tenon's capsule in the infero-nasal quadrant, ~6mm from the limbus
  • The tip of a pair of Westcott springed scissors is used to make an opening into the sub-Tenon's (episcleral) space

  • A blunt, curved, 19G sub-Tenon's cannula (25mm) is advanced into the space until 15 - 20mm deep
  • This is used to infiltrate 2 - 5ml of LA into the space
    • The volume varies significantly between operators
    • High volumes can increase the IOP and shallow the anterior chamber during surgery

Specific complications

  • Patients experience pressure ± pain on injection
  • Subconjunctival oedema and haemorrhage can occur
  • Damage of the vortex veins
  • Although rare, if globe perforation does occur there is increased damage compared to sharp needle block

  • Peribulbar blocks are extraconal injections and use a short needle to improve safety profile
  • They have largely superseded retrobulbar blocks, but should still be avoided if axial length >26mm due to risk of globe perforation

Benefits

  • Good quality anaesthesia
  • Motor block
  • Reduced complication rate vs. retrobulbar block

Conduct

  • Patient lies supine and in primary gaze i.e. looking straight ahead
  • A 16mm, 25G (or smaller ie 27G) needle is inserted infero-temporally, lateral to the lateral limbus
  • It is aimed posteriorly and advanced parallel to the floor of the orbit
  • Some individuals ask the patient to look around during the injection to check no muscle is trapped in the needle
  • Needs 5 - 10ml LA for satisfactory block and may need supplementation with alternative blocks

  • Traditional retrobulbar block used sharp, 50mm needles, but the increased risk of sight- and life-threatening complications has reduced their use
  • The modified approach uses a short, 24mm needle to increase safety
  • The goal is to inject LA at the level of the posterior border of the globe to block:
    • The ciliary ganglion, causing pupillary dilation
    • Sensory nerves to sclera and cornea
    • Motor innervation of the extra-ocular muscles

  • The retrobulbar block benefits from causing rapid onset, high-quality anaesthesia and globe akinesis
  • However, its (relatively) high risk of significant complications has led it to fall out of favour compared to other techniques

  • Block conduct is very similar to the peribulbar block, though once the needle reaches the globe equator it is redirected medially and superiorly to enter the muscle cone at the level of the posterior border of the globe

  • Chemosis (conjunctival swelling) is common, but is easily dispersed by gentle pressure
  • Subconjunctival haemorrhage
  • Corneal abrasion can occur, as the anaesthetised cornea is susceptible to injury or drying out
  • Muscle palsy from direct LA injection into muscle may lead to prolonged diplopia or ptosis

  • Allergy to local anaesthetic or hyaluronidase can occur
  • Local anaesthetic toxicity from intravascular injection

  • Failure
    • Signs a block is working include (relative) dyskinesia and ptosis (from levator palpabrae superioris paralysis)

Retrobulbar haemorrhage

  • The incidence is higher with retrobulbar (1%) than peribulbar (0.07%) blocks
  • Blood in the orbit causes proptosis and raised IOP
  • The increased pressure may impair retinal artery flow, leading to blindness
  • If suspected, one should alert the surgeon immediately as a lateral canthotomy may be necessary

  • The risk of retrobulbar haemorrhage is reduced by:
    • Use of sub-Tenon's block
    • Avoiding the supero-nasal quadrant, which is more vascular
    • Checking INR if patient on warfarin

Globe penetration, perforation or rupture

  • The incidence is higher with retrobulbar (1 in 140) than peribulbar (1 in 12,000 - 16,000) blocks
  • 50% of incidents aren't immediately recognised
  • Signs include:
    • Painful injection
    • Sudden deviation of globe
    • A 'soft' eye
  • Can lead to retinal detachment

Optic nerve damage

  • Overall rare
  • Injection into the optic nerve sheath is painful and may cause permanent nerve damage
  • Intrathecal injection, or injection into the dural sheath, may lead to brainstem anaesthesia and profound respiratory, cardiovascular and neurological sequelae
  • Management is supportive