• Ophthalmic anaesthesia
• Proxymetacaine 0.5% can be used to to anaesthetise the conjunctiva
• 25g sharp needles are commonly used as longer needles increase the risk of globe perforation
• Anatomy
• Bony anatomy
• Pyramidal structure
• Orbital rim to foramen = 42-54mm
• Apex has more vessels/optic nerve
• Globe
• Axial length 20-25mm in adults but longer in myopia
• Tenon's capsule is a thin membrane covering the globe, extending from the optic nerve to fuse with the conjunctiva anteriorly
• Muscles
• Congregate at the apex of the orbit to form a fibrotendinous ring which inserts into the globe
• The sensory nerves supplying the globe pass within this cone as do nerves III & IV
• The superior oblique lies outside the ring
• Nerves
• Optic nerve
• Enters the medial aspect of the globe
• Travels medially in the in the orbit to enter the optic foramen and is vulnerable here
• Sensory supply of the globe is via the long and short ciliary nerves (branches of the opthalmic branch of the trigeminal nerve)
• Vessels
• Opthalmic artery is a branch of the IC artery
• Venous drainage is via the superior and infereior opthalmic veins
• Complications
• Not much good evidence for any technique over another currently
• Retrobulbar haemorrhage 1-2%
• Inform surgical team immediately
• Globe perforation (<1%)
• Leads to retinal detachment
• Commoner in myopia
• Pain on injection is common
• Optic nerve damage (<1%)
• Commoner with medial compartment block or looking in and up during inferotemporal injection
• Can cause CNS toxicity and pain on injection
• LA toxicity
• Can be due to injection into CSF so need resus equipment nearby
• Muscle palsies
• Avoid injection directly into muscles
• Chemosis
• Common and relieved with pressure and time
• Corneal abrasion
• Can occur during anaesthesia, procedure or post-op
• Contraindications
• Relative
• Myopic patients
• Pts unable to lie flat for duration of procedure
• Children
• communication difficulties
• Scleral buckling
• Bleeding diathesis (INR >3 if on warfarin)
• Absolute
• Patient refusal
• LA allergy
• Infection or marked inflammation
• Methods of block
• Peribulbar (extraconal)
  Link:m.youtube.com/results?q=peribulbar%20block&sm=
  
• 16mm 25g needle used with topical LA
• Neede is directed vertically backwards parallel to the floor of the orbit, lateral to the lateral limbus through the conjunctival reflection or percutaneously
• The needle tip should be extraconal, beyond the equator of the eye
• Retrobulbar
  Link:m.youtube.com/results?q=retrobulbar%20block
  
• Use topical as an adjunct
• A 24mm, 25g needle is inserted infrotemporally lateral to the lateral limbus or percutaneously
• The needle is directed vertically backwards until the equator is passed
• Once beyond the equator, direct slightly medially and upwards to enter the cone
• Supplementary blocks may be needed in some patients
• Supplementary blocks
• All peribulbar
• Superonasal
• Made through upper eyelid above medial limbus
• Medial canthus
• Needle inserted through conjunctiva, medial to the caruncle
• Keep parallel to the medial wall or risk optic nerve damage
• Sub-Tenon's
  Link:m.youtube.com/results?q=subtenon%20block&sm=1
  
• May be advantageous in myopic or anticoagulated patients
• Use LA for the conjunctiva and few drops of 5% iodine
• Use a lid speculum to keep eye open
• Get pt to look upwards and outwards
• Inferno nasal quadrant, 5-7mm from the limbus, a 2mm cut is made in the conjunctiva using moorfield's forceps and Westcotts scissors
• A blunt curved 19g, 25mm sub-Tenon's needle is used to deposit the local in the inferonasal quadrant beyond the equator
• Gentle side-to-side movement of the cannula may be needed
• CEACCP
  Link:ceaccp.oxfordjournals.org/content/6/5/203.full.pdf?sid=5b4323b4-16e3-4c66-9df9-b65edc8cf844