5.5 Ophthalmic

Question 1

Fissures in the orbit

Answer 1

The optic foramen,
the superior and
the inferior orbital fissures are the
most important fissures in the orbit.

Question 2

The optic foramen transmits

Answer 2

The optic foramen transmits
the optic nerve
and ophthalmic artery.

Question 3

The superior orbital fissure transmits

Answer 3

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):

Question 4

The inferior orbital fissure transmits

Answer 4

The inferior orbital fissure transmits the zygomatic branch of the
maxillary nerve (V2).

Question 5

The annulus of Zinn encircles

Answer 5

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.

Question 6

Motor supply of the eye muscles

nerves

Answer 6

SO4, LR6)

Oculomotor nerve

Trochlear nerve

Abducens nerve

Question 7

Oculomotor nerve

Answer 7

Muscle Nervous supply Actions
Medial rectus Adduction

Inferior rectus Depression, adduction,
extortion

Superior rectus Elevation, adduction,
intortion

Inferior oblique Extorsion, elevation,
abduction

Question 8

Trochlear nerve

Answer 8

Superior oblique
Trochlear nerve
Intorsion, depression,
abduction

Question 9

Lateral rectus

Answer 9

Lateral rectus Abducens nerve

Abduction

Question 10

Intraocular muscles

Answer 10

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

Question 11

Facial muscles

Answer 11

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

Question 12

The sensory supply of eye

Answer 12

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

Question 13

Retrobulbar (intraconal)

blocks

doesnt block

Answer 13

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.

Question 14

Peribulbar (periconal)

differs in whats blocked to retrobulbar how

Answer 14

Peribulbar (periconal) block often
results in

diffusion of LA to orbicularis oculi,
rendering the facial nerve block unnecessary.

It blocks the trochlear as well

Question 15

ophthalmic anaesthesia requires:

Answer 15

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).

Question 16

Topical anaesthesia is frequently employed

Answer 16

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.

Question 17

first agent used for topical

by who

what issues

Answer 17

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.

Question 18

Cocaine toxicity

Answer 18

Cocaine toxicity manifests as

biphasic CNS effects
(stimulation followed by depression),

sympathetic stimulation,
hyperthermia,
pupillary dilatation and
feeling of crawling insects on the skin.

Question 19

Controlling Cocaine tox s/e

HTN

prob with what

Answer 19

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.

Question 20

Max coke dose for eyes

Answer 20

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.

Question 21

Retrobulbar block

Where is the injection

Answer 21

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.

Question 22

What does Retrobulbar need to be combined with

Which onset is faster / denser

Answer 22

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.

Question 23

Retrobulbar describe process

Answer 23

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.

Question 24

Is atkinson position recommended

Answer 24

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.

Question 25

Non cutting (23G) vs cutting

Answer 25

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.

Question 26

Retrobulbar top up

Answer 26

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.

Question 27

Retrobulbar Complications

Answer 27

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

Question 28

Retrobulbar globe perforation

RF

Answer 28

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.

Question 29

Retrobulbar globe perforation presentation

Answer 29

It presents as

intense and immediate pain
with sudden loss of vision.

Surgery may need to be
postponed and retinal treatment undertaken

Question 30

Retrobulbar haemorrhage

presents

Answer 30

Retrobulbar haemorrhage (1%–3%)

is the most common complication
following retrobulbar injection.

It presents with pain, increasing
proptosis and frequently subconjunctival
or eyelid ecchymosis.

Question 31

Retrobulbar haemorrhage

what should be monitored

x2

Answer 31

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.

Question 32

Retrobulbar haemorrhage

Rx

Postponing surgery?

Answer 32

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.

Question 33

RF for RB bleed

Answer 33

Risk factors may be
previous retrobulbar bleeds,
vascular or haematological disorder.

Question 34

Peribulbar (periconal) block

benefit

drawback

Answer 34

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.

Question 35

Peribulbar

Describe

Answer 35

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.

Question 36

Peribulbar

Answer 36

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

Question 37

Sub-Tenon’s block

Answer 37

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

Question 38

Sub-Tenon’s block

describe

Answer 38

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

Question 39

Which cannulae are best for subtenons

why

Answer 39

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.