Download STRUCTURE OF THE EYEBALL Connective tissue layer = Sclera +

HFA 213 Week 12 The Orbit
STRUCTURE OF THE EYEBALL
Connective tissue layer = Sclera + Cornea
Vascular layer = Choroid + Iris
Neural layer = Retina
INTRA-OCULAR SMOOTH MUSCLE
Ciliary muscle
Accommodation (focussing)
Circular and longitudinal fibres
Both act to allow the lens to become more spherical (close up)
Nerve supply: parasympathetic fibres in Oculomotor (CN III) nerve
Pupillary muscles (sphincter and dilator)
Control pupil size (aperture)
Sphincter Pupillae
Circular muscle in inner 1/3 of the iris
Nerve supply: parasympathetic fibres in Oculomotor (CN
III) nerve
Dilator Pupillae
Radial muscle in outer 2/3 of the iris
Ciliary body, Suspensory ligament and lens
Vitreous humor
Aqueous humor (Anterior and Posterior chambers)
Nerve supply: Sympathetic fibres from superior cervical ganglion
Light reflex
Increased light on retina (Optic nerve - CN II)
Pupil constricts (Oculomotor nerve - CN III)
Accommodation reflex
CN III - focus, constrict, converge
HFA 213 Week 12 The Orbit
GEOMETRY OF THE ORBIT
EXTRA-OCULAR STRIATED MUSCLES
THE ORBITS DIVERGE
but
THE OPTIC AXES ARE PARALLEL
The rectus muscles
The origin of the rectus muscles is from a tendinous ring
surrounding the optic foramen.
The rectus muscles attach in front of the equator of the eye
They pull posteriorly and medially.
Therefore the superior and inferior rectus muscles adduct as
well as elevate and depress the eye.
Medial and lateral rectus are pure adductors and abductors
Elevation is performed by superior rectus and inferior oblique
The oblique muscles
The oblique muscles attach behind the equator
They pull anteriorly and medially
Therefore they abduct the eye
Depression is performed by inferior rectus and superior oblique
Intorsion and extortion cancel each other out
HFA 213 Week 12 The Orbit
ELEVATION AND DEPRESSION
Acting alone, superior oblique will turn the eye “down and out”.
BUT
People with a trochlear nerve lesion can’t look at the end of their nose.
BECAUSE
Superior oblique never acts alone.
It works with inferior rectus to depress the eye.
NERVES OF THE ORBIT
The Optic nerve (II) enters through the optic canal
Other nerves enter through superior orbital fissure:
Three enter outside the tendinous ring:
Lacrimal nerve (V1)
Frontal nerve (V1)
Trochlear nerve (IV)
These are all found superficially just under the orbital roof
If the eye is abducted
Inferior rectus is an effective depressor
Superior oblique can only cause intorsion
Three enter inside the tendinous ring:
Oculomotor nerve (III)
Nasociliary nerve (V1)
Abducens nerve (VI)
These are located deeper
inside the cone of muscles
If the eye is adducted
Inferior rectus can only cause extorsion
Superior oblique is the effective depressor
The branches of the Ophthalmic (V1) are all sensory:
Frontal => Supraorbital and Supratrochlear
Lacrimal supplies lateral part of upper eyelid (and receives
some parasympathetic fibres from the pterygopalatine ganglion)
The same applies to superior rectus and inferior
oblique which couple to produce effective
elevation of the eye
The Nasociliary supplies the surface of the cornea (long
ciliary nerves) and has branches to the ethmoid air cells,
nose and nasal cavity
HFA 213 Week 12 The Orbit
AUTONOMIC NERVES OF THE ORBIT
MOTOR NERVES OF THE ORBIT
Nerve lesions:
1. Intraocular smooth muscle (short ciliary nerves)
Parasympathetic (Oculomotor nerve and ciliary ganglion)
Sphincter pupillae and ciliary muscle
Sympathetic (via internal carotid plexuses)
Trochlea nerve (IV) - Supplies superior oblique muscle
Patient has trouble depressing the adducted eye can’t look at
tip of nose, or at feet going down stairs
Dilator pupillae
2. Extraocular smooth muscle (Sympathetic)
Superior tarsal muscle (in levator palpebrae superioris)
“Muller’s” muscle (Not well understood – or seen) holds the eye in the
In order to avoid diplopia, the patient tends to tilt head
because the affected eye also becomes extorted (rotated
by the unopposed action of inferior oblique)
front of the orbit
3. Lacrimal gland
Parasympathetic fibres from pterygopalatine ganglion
initially carried with the
zygomatic nerve transfer to the
lacrimal nerve
Abducens nerve (VI) – Supplies lateral rectus muscle
Patient has trouble abducting the affected eye.
In order to avoid diplopia, the patient tends to look sideways
so that the affected eye can be used in adduction.
Oculomotor nerve (III) – Supplies all other extra ocular
muscles as well as parasympathetic innervation to
intraocular muscles
Horner’s Syndrome: Damage to the cervical sympathetic trunk:
1. Ptosis - drooping of the upper eyelid (loss of superior tarsal muscle)
2. Miosis - pupillary constriction (loss of dilator pupillae)
3. Enophthalmia – sunken eye (loss of Muller’s muscle)
4. Anhydrosis – loss of facial sweating and vasodilatation
Patient has trouble with:
Elevating the eye or upper eyelid
Close-up vision:
Lens accommodation
Constricting the pupil
Adducting the eye