Dr S Wu. FACRRM, FRACGP
Dr KC Tang. FRANZCO, Clinical lecturer School of Rural Health, University of Sydney
Anterior
Sub-Tenon’s Anaesthesia (ASTA)
for Cataract Surgery
Introduction
Ocular regional
blocks
1 = Anterior SubTenon’s Anaesthesia
(ASTA)
2 = Steven’s subTenons Technique.
3 = Retrobulbar
4 = Peribulbar
Tenon’s Capsule
Like a glove for the whole
eye
Starts at the limbus and lid
muscles
Initially fused to
conjunctiva
Loose matrix
Follows sclera around the
globe
Sleeves around rectus and
oblique muscles
Attaches to optic nerve
sheaths
Posterior instrumentation unnecessary
for Sub-Tenon’s (ST) Block
McNeela et al (2004) N=59
Successful ST blocks
6mm ultra-short cannula
Kumar et al (2004) N=151
compared 3 sub-Tenon’s
cannulae lengths:
25mm
18mm
12mm
Sub-Tenon’s space
accessed
anteriorly!!!
Short cannula
achieved similar
anaesthesia and
akinesia
Needle sub-Tenon’s injection
Ripart et al (1996) N=151
Unlike cannula ST
techniques
25G needle without
dissection
Medial canthus subTenon’s injection
Mean depth 15-20mm
92% - total akinesia
Dissection not
necessary for
sub-Tenon’s
block
Ripart (1998)
CT images of fresh cadavers
9mls contrast given by MC
sub-Tenon’s injection
spread to:
Episcleral space
Optic nerve sheath
Rectus muscle sheath
Lid muscles- orbicularis
occuli & levator palpabrae
Subconjunctival space
Short needle
25G 16mm
Methods
Case series
60 adult elective cataract patients
All received ASTA by author
Using 2 common local anaesthetics
30 – lignocaine 2% +hyalase 30 iu/ml
30 – bupivacaine 0.5% + lignocaine 2% + hyalase 30 iu/ml
Approved by regional HERC
ANZCTR
Preparation
Routine pre op care
Supine, eye pillow
½ strength iodine
Head stabilised by
nurse
Amethocaine 1% x1
drop
Optional light sedation
(midazolam)
ASTA Technique Outline
Lift upper lid, look down
Pierce conjunctiva and Tenon’s
capsule in upper outer quadrant
5-7mm from limbus
Advance needle about 5mm
supero-medially
Following curve of sclera
Visually check needle position by
forming a small bleb of L.A.
Inject L.A. VERY SLOWLY, guided by
patient comfort
Vol. 6-10mls, diff in each patient, guided by 3 signs of
filling up the ST space as described by Ripart :
Mod. proptosis + lid fullness + mod. chemosis
At the end of ASTA
injection, complete
lid drop evident
Excess chemosis
Mostly resolves with gentle
massage
Akinesia
Scored 10min post ASTA, using Aggregated Motility Score
(AMS)
Validated scale used by Kumar, MaNeela, Brahma etc
Lid + Globe mvt in 4 directions: up, down, medial, lateral
0 = no mvt
1 = twitch <1mm
2 = partial mvt
3 = full mvt
Total akinesia = 0, adequate akinesia < =4, max mvt = 15
Pain
Rated as it occurred during operation
Numeric Verbal Rating Scale
0 = no pain
1-3 = mild
4-6 = moderate
7-9 = severe
10 = worst
Results
Mean age 74, equal gender.
All successfully completed surgery
without supplemental anaesthesia
No major anaesthetic complications
No surgical complications due to ASTA
Main complication = Sub conjunctival
haemorrhage in 5% pts.
48% on warfarin or antiplatelet Rx
Akinesia 10min post ASTA
18
•95% - AMS ≤4/15
16
•100% - lid paralysis :
levator palpabrae and
orbicularis occuli
14
12
10
Lignocaine
Lignocaine/Bupivicaine
8
6
4
2
0
AMS 0 AMS 1 AMS 2 AMS 3 AMS 4 AMS 5 AMS 7
Pain during operation
•58/60 pain free
35
30
•2 patients- Transient
mild pain 1-2/10
25
20
Lignocaine
15
Lignocaine/bupivacaine
10
•End of procedure
•No supplementation
required
5
0
Pain 0
Pain 1
Pain 2
Discussion
ASTA comparable
to other sub-Tenons
blocks
Akinesia 95% AMS ≤ 4
Learning curve
McNeela et al (2004)
98% AMS<4
Kumar 3 cannulae (2004)
92-100% AMS<4
Koh et al, Concord Hosp,
2005, Steven’s sub-Tenon’s
block
Akinesia - 88% AMS≤4
Anaesthesia – 7% needed
topical amethocaine
supp.
ASTA - Comprehensive all-in-one block
Relatively large volume
Av = 9mls (similar to Ripart)
One injection delivers LA to:
Lid muscles, no need VII inj.
Sub-conjunctival space
Muscle sheaths
Episcleral space
Retrobulbar space
Implications for Safety
ASTA
Anterior
Visually guided
Short needle
Less invasive – no
dissection
Improve Aesthetics &
healing
Reduce infection
Avoids vulnerable anatomy
Optic and other
nerves
CSF
Blood vessels
Retina / macula
Should be safer
Potential Advantages
Globe perforation
Anterior
Peripheral retina
Visible
Haemorrhage - anterior
Seen
Compressed
No need to stop Warfarin or
antiplatelets
?Safer in axial length ≥ 26mm
Equipment is cheap & readily
available – beneficial for
developing nations
Easily topped up anytime
?Role in patients with
difficult access
Previous surgery
Adhesions
Scleral buckles
Conclusion
Small study
ASTA
Simple
Effective
Safe
Phaecoemulsification
cataract surgery
Further research to
elucidate its wider
application
“Simplicity is achieving
maximal effect with
minimal means”
Dr Kawana
Contact: drwu@bigpond.com
Zen Garden Master.