Ophthalmology Flashcards
SS_OP 1.5:
Discuss the use of adjuvant drugs for regional eye blocks and in particular Hyalase
What’s hyaluronidase & what does it do?
What are the benefits of hyaluronidase? risks?
other adjuvants?
enzyme causing hydrolysis of hyaluronic acid, a glycosaminoglycan forming part of the extracellular matrix. This increases tissue permeability & promotes dispersion of LA.
facilitates speed of onset & quality of the block
range of concentrations from 5-70IU/mL; product info recommends 25 IU/mL (ie. dilute one ampule in 1.0mL sterile distilled water or the LA solution (this will mean 0.1mL has 150 IU, added to 6mL LA will give 25IU/mL).
Increases tissue permeability of the LA
facilitates speed of onset
enhances quality of block
Promotes dispersion of the LA
reduces the increase in orbital pressure associated w the injected volume
reduces risk injury to extraocular muscles (eg. less risk myotoxicity due to faster spread)
clonidine enhances intra- & post-op analgesia when added to the LA
Dose of 1mcg/kg does’t inc incidence of systemic adverse effects (hypoT, excessive sedation)
May help prevent intra-op arterial HTN, may lower IOP
Adr: less commonly used to enhance duration of eye block since long-acting LAs
LA doesn’t spread inside globe so unlikely to cause vasospasm & subsequent retinal ischaemia.
What else (unrelated to ophthal) can hyaluronidase be used for?
Extravasation of a vesicant
Considerations when doing a GA for eyes?
accessibility
airway selection- generally a SGA
adequate depth/relaxant
environmental issues
What are some common co-morbid disease & pt factors encountered in pts having ophthalmic procedures? (also consider for paediatrics)
often elderly
DM, IHD, COAD, obesity
anticoagulants
issue with lying flat- can work around- just the eye level needs to be flat for microscopy so could prop & make sure just head flat
anxiety/fear level (perception, advice from surgeons/friends)
What’s normal axial length?
Axial length 22-25mm, long >26mm short <22mm
What’s normal IOP? Ocular HTN?
10-21mmHg, ocular HTN >21mmHg
What’s glaucoma?
visual loss due to damage to the optic nerve
What’s staphyloma?
protrusion of sclera due to thinning
prevalence increases with axial length.. More common in extreme myopia.
What’s an example type of eye inflammation/infection for which intracameral injection of antibiotic into the anterior chamber of the eye for cataract surgery is performed?
endophthalmitis
What are some surgical factors to consider for ophthalmologic procedures?
Often “remote location”- standalone facility/distant to major hospital, regional centre
May not be familiar with team
they may not be as practiced with anaesthetic emergency procedures/resus
Type
Duration
Akinesia needed? (particularly vital for vitrectomy)
Toric marking needed?
Postop positioning
SS_OP 1.3: What’s the oculocardiac/aschner/trigeminocardiac reflex?
traction on extra ocular muscles/pressure on globe, ocular manip/pain–> severe bradycardia (?<20% of baseline), junctional rhythm or asystole.
mediated by connections of ophthalmic branch (V1) of trigeminal cranial nerve afferents (which is formed by merging of short & long ciliary nerves) synapsing with visceral motor nucleus of the vagus nerve (PSNS) in brainstem. Efferents from the cardiovascular vasomotor centre in the medulla then inhibit the SA node.
less pronounced with older age (frequent +++ with kids & squint surgery)
For all of the reflexes (oculocardiac, oculoresp, oculoemetic):
-afferent arm= V1 (ophthalmic division of trigeminal nerve) via long & short ciliary nerves converging on ciliary ganglion, to trigeminal ganglion near floor 4th ventricle
-efferent= vagus (fibres to resp, vomiting centre, SA node)
-risk factors: worse with hypoxia, hypercarbia, acidosis, light anaesthesia, younger age.
-prevention:
Could consider prophylaxis with block (LA reduces incidence since blocks the afferent limb (via trageminal nerve) of the reflex), extra LA, anticholinergic (consider pre-op glyco), avoid hypercarbia (sensitises the reflex)
-Mx: immediately stop stimulus, consider atropine (eg. 20mcg/kg IV)/glyco, optimise oxygenation/ventilation, deepen anaesthesia, CPR if severe
SS_OP 1.3: What’s the oculorespiratory reflex?
pressure on globe/traction on extraocular muscles, ocular manip/pain–> reduce RR, shallow breathing, lead to irregular resp movements & risk resp arrest
mediated by connections of ophthalmic branch (V1) of trigeminal cranial nerve afferents (formed from convergence of short & long ciliary nerves) which communicates with the pneumotaxic respiratory centre of the pons which signals the medullary respiratory centre &, via phrenic & other respiratory nerves, lead to bradyphrenia, irregular respiratory movements, risk respiratory arrest
Reflex sometimes occurs with strabismus surgery, sometimes masked by controlled ventilation, pt who’s spont breathing should be carefully monitored, may cause hypoxia/hypercapnia.
atropine doesn’t impact the reflex.
SS_OP 1.3: What’s the oculoemetic (trigemino-vagal) reflex?
traction on extraocular muscles, pressure on globe, ocular manip/pain–> nausea & vomiting
ophthalmic division of trigeminal nerve carries impulses to main sensory nucleus of the trigeminal nerve
vomiting center in the medulla causes increased vagal output–> nausea & vomiting.
incr PONV risk so administer prophylaxis (multimodal), limit fasting time, promote hydration, consider limiting emetogenic meds.
Retrobulbar or peribulbar blocks decrease afferent signaling & reduce incidence of the oculo-emetic reflex
common ++ with squint surgery (60-90%)
Discuss cataracts
For “cloudy lens”
very common, rapid (approx 5 mins in experienced hands)
Surgeons perform 3x incisions between iris & cornea, inject viscoelastic solution to keep enough pressure in chamber/ not collapse
Capsular recess (break into the anterior capsule) & insert machine with ultrasonic waves to break the lens into fragments, vacuum to remove them. Insert a new lens held in place with some hooks.
Often insert antibiotics- generally the incisions heal themselves, may glue or very rarely suture.
Major complication to avoid= posterior capsule tear.
Anaesthetic: can be ANY technique- GA–> no sedation, regional can be topical/ subconjunctival/ intracameral/ retrobulbar/ peribulbar/ subtenon
What are advantages & disadvantages of regional +/- sedation for ophthalmic anaesthesia?
Advantages of regional:
Minimal disruption to life/living
Avoid GA/minimal exposure to sedatives
Rapid discharge
Faster turnover=more pts
Ease & speed for postop positioning
Disadvantages:
Pt cooperation
Language barrier
Fear/anxiety
Body comfort- unable to lie flat/pain
Sedation can be tricky- too deep may be dangerous
O2 supplementation minimal
How do topical anaesthesia for cataract? pros & cons
Oxybuprocaine 0.4% 3 or so drops to the conjunctival sac 5-10mins before surgery, or tetracaine 0.5%, both esters, use prior to iodine prep/eye block.
Can only do if calm/cooperative pt, simple pathology, amenable surgeon, happy anaesthetist.
Advantages= negates risks with GA/other regionals, minimal pain on application, no change in IOP, able to move eyes & rapid recovery of ocular function
Cons cf subtenon: only blocks trigeminal nerve terminals in cornea & conjunctiva- poorer intraop pain relief despite less pain with administration (no anaesthesia to intra-ocular structures) pt & surgeon satisfaction (no akinesia of the globe), incr posterior capsule tear, vitreous loss 4.3% cf 2.1% (cochrane 2007 subteons vs topical for cataract)
How to do subconjunctival or intracameral block?
Small volume, direct injection into anterior chamber or subconjunctiva often by surgeon intraop
supplement topical or if there’s an incomplete block for anterior procedures
ameliorates the pressure effects of hydro-dissection (used during phacoemulsification cataract surgery) which can be uncomfortable & is not blocked by topical anaesthesia alone
pain relief is rapid
preservative-free 1% lidocaine
What are the “sharp needle blocks”?
Extra-conal (outside the fibromuscular cone formed by the 4 rectus muscles- the cone is incomplete (particularly posteriorly) so LA distributed to both sides of the fibromuscular cone as volumes increase)= inferolateral peribulbar or medial canthal peribulbar
intra-conal= retrobulbar, behind the eye within the fibromuscular cone
What’s the advantage of peribulbar over retrobulbar?
less uncomfortable for pt (but less comfortable than subtenon’s)
peribulbar is extraconal- aims to avoid iatrogenic injury vessels & optic nerve, as outside the fibromuscular cone, LA aiming to spread across the fibromuscular cone.
retrobulbar is intra-conal. more marked proptosis (smaller volume adequate) & may miss the trochlear (motor for sup oblique) & the frontal/lacrimal branches of V1 (sensory to peripheral conjunctiva)
How to do a peribulbar? What’s the max insertion depth for inferolateral & medial canthal peribulbar?
extraconal injection of LA
LA topicalisation & sterilisation
eye in neutral gaze
Inferolateral: can either go perconjunctival or skin. if L) eye, open eye w L) thumb, steady the needle hub, enter @ inferolateral 1/3 (far inferotemporal corner of eye), needle passed posteriorly, parallel to floor of orbit until beyond equator of globe.
25g insertion depth limited to 25mm.
Negative aspiration before inject to avoid globe injection.
6-10mL (LARGER volume than retrobulbar; allows spread to intraconal space & spread to lids (to block orbicularis muscle so don’t need additional lid block). Pt may c/o a pressure-like headache that subsides within minutes.
max needle depth for medial canthal (btwn caruncal & medial cants) peribulbar= 12.5mm- angle towards upper medial quadrant to limit risk of injecting into medial rectus. Myopic staphyloma (risk factor for perforation) infrequent here.
- may use a blunter atkinson needle which may help identify encounter of scleral tissue (relatively blunt) but may use sharper needle as theoretically less damage if did perf globe.
Classically peribulbar described as the 2 injections- 6-10mL at the inferotemporal site & 3-5mL at the medial canthal site.
Pros: less major complications (posterior globe perf, optic N injury, haematoma, brainstem anaesthesia) than intraconal, no need for additional block for lid akinesia (the larger volume of LA spreads to orbicularis oculi)
Cons:
slower onset than retrobulbar
conjunctival chemosis more common w peribulbar vs retrobulbar
less akinesia of orbit than retrobulbar (given the spread of LA may be unpredictable; additional LA may be required but rule of thumb= only do supplemental injection (eg. 2nd approach) if a single injection was insufficient anaesthesia since anatomic distortion w the 1st inj risks compns w consecutive injns.
if insert too deep (>25mm) risk unintentional retrobulbar, damage rectus mm & optic nerve.
How does the retrobulbar differ to the peribulbar?
Aiming intra-conal
smaller volume cf peribulbar
marked proptosis
What’s tenon’s fascia?
connective tissue enveloping eyeball
begins anteriorly at the corneoscleral junction (limbus), fuses posteriorly with the dural sheath of the optic nerve. (cornea= transparent part of eye covering iris & pupil. sclera= white outer layer of eyeball).
separates the globe from extra- & intra-conal fat which surrounds the ocular muscles
pierced by muscles/nerves
creates a potential space around the eye into which LA can be placed, allowing diffusion of drug to nerves innervating the eye & its muscles
What’s subtenon’s space?
potential space btwn tenon’s capsule & sclera.
Describe the “blunt needle technique” of sub tenon’s
1% ropiv & 2% lig
hyalase no diff onset & risk anaphylaxis
L) UL IVC (closest to us)
for LA drops, lower lid down & pt look up
syringe set so can see the mL marks
Inferonasal location. Avoid muscle insertions, avoid vortex vein
Pt has had phenylephrine & LA drops
Apply chlorhex prep
Barraquer speculum
Pt look up & out, hold gaze to expose inferonasal quadrant (avoids insertion of the oblique muscles & surgical site)
Steady hands
non-toothed forceps taking conjunctiva & tenon’s fascia 5-10mm from limbus (avoid blood vessels & pterygia) & small vertical cut with Wescott scissors to expose underlying white sclera. may pass the closed scissors around the globe to create a passage following contour of eye (optional)
With hand grip over needle, advance blunt needle around the curvature of the eye (keeping tenon’s fascia close to globe so minimal stretch), blunt curved short 18-20g, 12mm cannula past equator (syringe vertical) before inject so LA posterior to equator of the globe, so LA spreads back to optic nerve (if a lot of LA spills forward not advanced far enough)
3-5mL for good anaesthesia & early akinesia; accessing episcleral space allows LA to spread circularly around scleral portion of globe under Tenon’s fascia with good analgesia of whole globe w relatively small volumes. larger volumes (8-11mL) provides spread to extra-ocular m sheaths for more reproducible akinesia.
gentle pressure to improve spread & reduce chemosis.
Issues with subtenon’s:
while it’s the least painful injection method & has lower risk of major (eg. globe perforation) complications & has rapid onset (approx 5 mins) & highest success for anaesthesia (>97%, vs >=84% for peribulb, >85% retrobulb):
pt cooperation (pt MUST look up & out to maximise field) -requires much more pt cooperation cf peribulbar
limited field
pt may have scarring/oedema of conjunctiva or be very vascular or pterygium
Scleral buckle limits insertion of tenon cannula (is a contraindication, as is infection). Prior retinal or glaucoma surgery= relative contraindicaitons.
variable akinesia (volume-dependent)
The minor complications (chemosis (common ++ with subtenon’s if gone through conjunctiva but not capsule, can happen with peribulbar too)/subconjunctival haemorrhage/conjunctival VD causing red eye) more common (surgeon’s not so keen for cosmetic reason- the redness will go away in approx 1 week) with sub-tenon’s but more major (eg. retrobulbar haemorrhage) with peribulbar
What are the risks with LA for eye?
Explain to pt that they may see unusual shapes/shadows/kaleidoscope effect of colours in operative eye
Minor complications of regional for eye (4.3%)
Chemosis
Subconjunctival haemorrhage (may persist for 1/52)
Major- sight- or life-threatening- very rare (0.066%)-
Direct needle injury (globe (3 in 4000 for retrobulbar, 1 in 16224 peribulbar), vessel (retrobulbar haemorrhage risk 0.1-1%, no evidence sharp needle higher risk than subtenon’s!), optic nerve (needle into sheath), ocular muscle (direct trauma, ischaemia or LA myotoxia))
Spread of LA (optic sheath (may get brainstem anaesthesia), vessel, intraocular)
Excessive pressure to optic nerve through compression
Allergy (LAST)
Sharp needle technique 2.3x lower rate minor complications, 2.5x increased risk major complications cf subtenon
What’s the risk of minor & major complications with sharp vs blunt needle techniques?
Sharp needle technique 2.3x lower rate minor complications, 2.5x higher rate major complications
What are the risks of globe injury with retrobulbar vs peribulbar?
3:4000 retrobulbar
1:16224 peribulbar
what’s the globe volume?
7mL
normal axial length?
22-24mm
what are the 2 different types of globe injury?
perforation (2x puncture wounds- entry & exit) vs penetration (1x entry wound)
symptoms of globe injury? risk factors for globe injury? Mx?
severe pain on injection, hypotonia (if LA injected, hypertonia), sudden loss of vision/visual acuity changes, vitreous haemorrhage or poor red reflex.
May get loss of vision via a choroidal heamorrhage, retinal detachment, vitreous haemorrhage or scar tissue formation. May be sight-threatening.
risk factors:
Pt: myopic (axial length >26mm), thinner eye, deep set eyes, previous scleral buckle, posterior staphyloma (staphyloma more common in myopes)
Technical: Injecting LA in globe may cause rupture, multiple injections, sharp needles.
Mx= immediate ophthalmological opinion
