Opthalmology

Question 1

How long will 2% lidocaine last for in eye block vs 0.5% levobupivicaine

Answer 1

45 mins vs up to 24 hours

Question 2

Absolute and relative contraindications LA blocks eye surgery

Answer 2

Absolute ci are refusal, LA allergy, localised infection
Relative ci are inability to lie still, communication difficulties, confusion, grossly abnormal coagulation, perforated globe or trauma

Question 3

Average axial length

Answer 3

25mm

More than 26 mm myopes risk of perforation in retro and peribulbar blocks

Question 4

Muscles of eye

Answer 4

4 recti - origin annulus of zinn
2 obliques
Levator palpebrae
Orbicularis occuli

Inferior oblique only muscle to have anterior origin.

Question 5

Nerve supply eye

Answer 5

Sensory -
Optic nerve
Opthamic branch trigeminal ( nasocillary- intraconal lacrimal, frontal extra conal) via SOF

Motor
3, So4 lr6
Trichlear extraconal

Question 6

Normal IOP and what factors effect IOP

Answer 6

IOP is 10-20mmhg

IOP depends on
Changes in intraoccular contents (balance between inflow and outflow aqueous humour)
Sclera rigidity
External pressure on eye

Question 7

Anticoagulants and antiplatelets in eye surgery

Answer 7

Continued in cataracts with normal therapeutic targets
Topical Anaesthetisia reduces risk in high inr

More complex surgery should discuss

Question 8

Drugs used in eye blocks

Answer 8

Local ie lidocaine or bupivicaine

Hyaluronidase

Question 9

Complications of regional eye anaesthesia

Answer 9

Chemosis 
Subconjunctival haemorrhage 
Pain
Retrobulbar haemorrhage 
Globe injury 
Optic nerve atrophy
Muscular palsy 
Brain steam anaesthesia

Question 10

Topical anaesthesia

Answer 10

Lidocaine 3.5%

Tetracaine 0.5%

Question 11

Subtenons how to do

Answer 11

Look up and out
Speculum to keep eye open.
Use inferior nasal approach
To other forceps, bite tenons fascia
Small cut to expose sclera, scissors closes to pass around globe to create passage
Subtenon needle follow contour globe until vertical
3.5ml injected

Subtenon cannula 25mm with flat curved tip

Question 12

Peribulbar block how to do

Answer 12

Inferior temporal
Posterior to equator then 5-10ml
Classically described as two injection - medial carbuncle to medial canthus second injection

Question 13

Describe orbit

Answer 13

Pyramidal shape with base front of eye ans apex pointing posteriormedial
Medial walls lie parrellel to each other
Lateral walls lie at 90 degrees
Length apex to rim 50mm
Cavity volume 30ml

Bones
Frontal
Zygomatic
Maxilla

Lacrimal
Ethmoid
Sphenoid
Palatine

Question 14

Describe eyeball

Answer 14

Lies anterior, superior lateral
Spherical shape
Average axial length of 25mm
Myopic eyes more than 26mm are at risk of staphylomata and increased risk of gloves rupture in peripbulbar block
Tenons fascia surrounds eye ball- arises at cornoscleral junction and fuses positively with Dural sheath of optic nerve - separates glove from intra and extraconal fat. Sub tenons space is a potential space around eyeball in which LA can be placed

Question 15

Describe muscles of eye

Answer 15

Levator palpabrae
6 extra ocular muscles 4 recti SIML 2 obliques SO IO

Recti arise from annulus of zinn and insert into sclera anteriorly
Narrow intramuscular membrane connects the recti = cone

Can inject LA into the cone = retrobulbar 3-5ml

Extraconal requires more LA as will need to diffuse into the space 5-15ml for peribulbar

SO arises near SR near annulus of zinn

IO only muscle that has an anterior origin at infraorbital rim

Question 16

Describe nerve supply of the eye

Answer 16

Sensory
Optic nerve leave via optic foramen
Ophthalmic branch of trigeminal (frontal lacrimal and nasocillary) pass through SOF
Nasocillary sensation to cornea and superior nasal conjunctiva - passes intraconal to long and short ciliary nerves
Lacrimal and frontal extraconal and supply rest of conjunctiva

Motor
Occulomotor nerve SOF passes intraconal
Trigeminal also SOF but extraconal so intraconal injection may result in trigeminal sparing (spared SO action)

Question 17

OCR describe

Answer 17

Parasympathetic bradycardia due to traction or pressure of globe

Trigeminal afferent to medulla
Efferent vagus nerve to SAN

Treatments
Stop action
Anticholinergics
Deepen anaesthesia

Reduce effects by LA and blocks

Question 18

Opthamic surgery prep considerations

Answer 18

General
Comorbidities ie CVS can’t lie flat, hypertension
Neuro can’t lie still, tremor

Eye
Previous surgery ie schleral explant topical rather than block
Staphylomata need perioperative USS by opthalmology
Axial length more than 26mm risk of perforation so subtenons

Question 19

Preoperative fasting eye surgery

Answer 19

If ga or sedation - routine fasting
Low dose sedation for anxiolytics not required fasting
LA alone normal diet and medication

Question 20

Before eye block

Answer 20

Position
Consent including may see unusual shapes shadows and kaleidoscope effects
Eye topical preparation - local anaesthetic( ie proxymetacaine) and pivodone iodine 5% solution

Question 21

Intracameral injection

Answer 21

By surgeon
Directly into anterior chamber
PF lidocaine