5.5 Ophthalmic Flashcards
Fissures in the orbit
The optic foramen,
the superior and
the inferior orbital fissures are the
most important fissures in the orbit.
The optic foramen transmits
The optic foramen transmits
the optic nerve
and ophthalmic artery.
The superior orbital fissure transmits
The superior orbital fissure transmits the following:
lie outside the annulus of Zinn.
lacrimal (V1),
frontal (V1) and
trochlear (IV):
lie inside the annulus of Zinn. oculomotor (III), abducens (VI) and nasociliary (V1):
The inferior orbital fissure transmits
The inferior orbital fissure transmits the zygomatic branch of the maxillary nerve (V2).
The annulus of Zinn encircles
The annulus of Zinn (tendinous ring) encircles the optic nerve, ophthalmic artery, superior branch of the oculomotor nerve, abducens nerve, nasociliary nerve and inferior branch of the oculomotor nerve.
Importantly, the trochlear nerve lies outside the annulus of Zinn.
Motor supply of the eye muscles
nerves
SO4, LR6)
Oculomotor nerve
Trochlear nerve
Abducens nerve
Oculomotor nerve
Muscle Nervous supply Actions
Medial rectus Adduction
Inferior rectus Depression, adduction,
extortion
Superior rectus Elevation, adduction,
intortion
Inferior oblique Extorsion, elevation,
abduction
Trochlear nerve
Superior oblique
Trochlear nerve
Intorsion, depression,
abduction
Lateral rectus
Lateral rectus Abducens nerve
Abduction
Intraocular muscles
Intraocular muscles
Iris sphinter muscles
(pupillary sphincter)
Parasympathetic (M3 rec) via
short ciliary nerves
Circular muscle contraction –
pupillary constriction
Iris radial muscles (pulpillary dilator) Sympathetic (α1 rec) via long ciliary nerves Radial muscle contraction – pupillary dilatation
Ciliary body Parasympathetic (M3 rec) via short ciliary nerves Ciliary body contraction, lens relaxation, loss of accommodation
Ciliary body Sympathetic (β2 rec) via short ciliary nerves Ciliary body relaxation, lens contraction, accommodation of eye
Facial muscles
Levator palpebrae
Ciliary nerves (striated muscle fibres) and
parasympathetic (smooth muscle fibres)
Opens the eye (elevates
eyelids)
Orbicularis oculi
Upper and lower zygomatic branch
Closes the eye (lowers
eyelids, blink)
Frontalis Elevates eyebrows
The sensory supply of eye
The sensory supply of the eye is
derived from the trigeminal nerve
through its
ophthalmic (V1) division
(frontal, nasociliary and lacrimal branches)
and maxillary (V2) division (infraorbital and zygomatic branches
Retrobulbar (intraconal)
blocks
doesnt block
Retrobulbar (intraconal) block provides for sensory anaesthesia, motor block of extraocular muscles and levator palpebrae,
but does not block orbicularis oculi. (eye can close)
This requires a separate facial nerve block.
Because the trochlear nerve lies outside the cone, it may be spared and allow
intortion, depression and abduction.
Peribulbar (periconal)
differs in whats blocked to retrobulbar how
Peribulbar (periconal) block often
results in
diffusion of LA to orbicularis oculi,
rendering the facial nerve block unnecessary.
It blocks the trochlear as well
ophthalmic anaesthesia requires:
1
Anaesthesia of cornea and conjunctiva
(topical anaesthesia or bulbar blocks)
2
Akinesia of the eyeball
(retrobulbar, peribulbar or sub-Tenon’s block)
3
Akinesia of levator palpebrae
(oculomotor and sympathetic) and
orbicularis oculi (facial nerve block).
Topical anaesthesia is frequently employed
Topical anaesthesia is frequently employed to
eliminate corneal and
conjunctival reflexes,
for eye surgeries and
diagnostic procedures.
Surgical advances and
less invasive techniques have made this possible.
first agent used for topical
by who
what issues
Although cocaine was the first agent
used for this purpose (Koller),
it is very toxic.
Hence other safer LAs like
proparacaine,
tetracaine and
lignocaine are commonly used.
Cocaine toxicity
Cocaine toxicity manifests as
biphasic CNS effects
(stimulation followed by depression),
sympathetic stimulation,
hyperthermia,
pupillary dilatation and
feeling of crawling insects on the skin.
Controlling Cocaine tox s/e
HTN
prob with what
The hypertension is best controlled
by an alpha and beta blocker
like labetalol.
Unapposed alpha action
resulting from only beta blockade (propranalol)
has caused lethal hypertensive exacerbation.
Max coke dose for eyes
All agents have some degree of corneal epithelium toxicity, cocaine
being most toxic. The dose should be restricted to 200 mg in a 70-kg
man (3 mg/kg) to minimise risk of toxicity.
Retrobulbar block
Where is the injection
Retrobulbar block is
an intraconal injection;
that is, it is given in the cone of
extraocular muscles producing
their akinesia with anaesthesia
of cornea and conjunctiva.
What does Retrobulbar need to be combined with
Which onset is faster / denser
Combined with a facial
nerve block for akinesia
of orbicularis oculi,
it permits eye surgery
under local anaesthesia.
Intraconal injection site produces faster onset, denser block and requires less anaesthetic than periconal injections.
Retrobulbar describe process
After anaesthetising the eye topically,
a 1.25-inch 23-G non-cutting edge
blunt needle is inserted
inferotemporally through
the lower eyelid,
directed superonasally with the eye
in inferonasal or neutral gaze,
injecting 3–4 mL of LA after negative aspiration.
Is atkinson position recommended
The traditional Atkinson position
of superonasal gaze during
inferotemporal needle placement is
not recommended, as it
results in rotation of the
posterior pole of the globe
into the path of the advancing needle,
increasing chances of optic nerve damage, globe
perforation or piercing of the meningeal sheath.
Non cutting (23G) vs cutting
Non-cutting-edge blunt needles
(23 G) have
higher scleral perforation pressures
than those with a cutting edge of a smaller gauge
(25 G),
as well as potential for more serious retinal damage should the perforation occur.
Retrobulbar top up
As the
trochlear nerve and superior oblique
lie outside the annulus of Zinn,
a residual intortion after the block may need a separate trochlear injection.
Retrobulbar Complications
Ocular complications include
perforation of the globe (0.1%),
retrobulbar haemorrhage (1%–3%)
and optic nerve damage.
Systemic complications include
intra-arterial injection, optic nerve sheath
injection and oculocardiac reflex
Retrobulbar globe perforation
RF
Risk factors for globe perforation include
an anteroposterior length of > 26 mm (high myopes),
severe enophthalmos,
previous scleral buckle,
repeated surgeries,
posterior staphyloma,
repeated injections
and
an uncooperative moving patient.
Retrobulbar globe perforation presentation
It presents as
intense and immediate pain
with sudden loss of vision.
Surgery may need to be
postponed and retinal treatment undertaken
Retrobulbar haemorrhage
presents
Retrobulbar haemorrhage (1%–3%)
is the most common complication
following retrobulbar injection.
It presents with pain, increasing
proptosis and frequently subconjunctival
or eyelid ecchymosis.
Retrobulbar haemorrhage
what should be monitored
x2
Following its occurrence,
the intraocular pressure and central retinal
artery pulsations should be monitored by an ophthalmologist for signs of impending retinal artery occlusion.
Because oculocardiac reflex
(trigeminal afferent, vagus efferent) can
be triggered several hours after its occurrence, ECG monitoring is a
must.
Retrobulbar haemorrhage
Rx
Postponing surgery?
Treating high pressures may
require a deep lateral canthotomy,
and if needed an
anterior chamber paracentesis.
Postponing the surgery is prudent,
with a general anaesthetic planned
for rescheduled surgery.
RF for RB bleed
Risk factors may be
previous retrobulbar bleeds,
vascular or haematological disorder.
Peribulbar (periconal) block
benefit
drawback
Peribulbar (periconal) block is made
outside the cone of extraocular
muscles,
theoretically reducing the
chances of retrobulbar haemorrhage
and
globe perforation.
But the onset is slower and
reinjections are frequently needed.
Peribulbar
Describe
After topical anaesthesia,
two injections are made,
first inferotemporally and then superonasally,
injecting 4–5 mL of LA at each site.
The needle is directed parallel to
floor of the orbit and advanced
only 1 inch (25 mm) just behind the
equator of the globe.
Peribulbar
Sometimes a medial transconjunctival
injection may also be made.
It is associated with the same incidence of postoperative ptosis as retrobulbar block, but eyelid ecchymosis is more
Sub-Tenon’s block
Sub-Tenon’s block
makes use of an
anatomical fascial plane
called Tenon’s capsule.
. The use of longer rigid metallic cannulae is associated with
higher complication rate (globe perforation, haemorrhage, muscle
trauma, brainstem anaesthesia, and orbital cellulitis). Therefore,
shorter plastic cannulae are preferable
Sub-Tenon’s block
describe
After topical anaesthesia,
with patient looking
outward and upward,
the inferonasal quadrant of conjunctiva is
nicked with blunt Wescott scissors,
and a curved cannula is inserted
onto the bare sclera below the Tenon fascia.
Then 4–5 mL of LA is injected,
resulting in rapid akinesia
proportional to the volume injected
Which cannulae are best for subtenons
why
The use of
longer rigid metallic cannulae
is associated with
higher complication rate
(globe perforation, haemorrhage, muscle trauma, brainstem anaesthesia, and orbital cellulitis).
Therefore, shorter
plastic cannulae are preferable.
