Orbit part 3 Flashcards
Describe the sensory innervation of the eyelids
The sensory nerves are all branches of the trigeminal nerve [V] (Fig. 8.79). Palpebral branches arise from:
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the supra-orbital, supratrochlear, infratrochlear, and lacrimal branches of the ophthalmic nerve [V1]; and
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the infra-orbital branch of the maxillary nerve [V2].
Describe the motor innervation of the eyelids
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the facial nerve [VII], which innervates the palpebral part of the orbicularis oculi;
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the oculomotor nerve [III], which innervates the levator palpebrae superioris; and
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sympathetic fibers, which innervate the superior tarsal muscle.
Summarise the consequences of different nerve injuries to nerve supplying the eyelid
Loss of innervation of the orbicularis oculi by the facial nerve [VII] causes an inability to close the eyelids tightly and the lower eyelid droops away, resulting in a spillage of tears.
Loss of innervation of the levator palpebrae superioris by the oculomotor nerve causes an inability to open the superior eyelid voluntarily, producing a complete ptosis.
Loss of innervation of the superior tarsal muscle by sympathetic fibers causes a constant partial ptosis.
What is Horner’s syndrome and describe its main features
Horner’s syndrome is caused by any lesion that leads to a loss of sympathetic function in the head. It is characterized by three typical features:
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pupillary constriction due to paralysis of the dilator pupillae muscle,
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partial ptosis (drooping of the upper eyelid) due to paralysis of the superior tarsal muscle, and
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absence of sweating on the ipsilateral side of the face and the neck due to absence of innervation of the sweat glands.
Describe some secondary changes that can occur as a result of Horner’s syndrome
ipsilateral vasodilation due to loss of the normal sympathetic control of the subcutaneous blood vessels, and
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enophthalmos (sinking of the eye)—believed to result from paralysis of the orbitalis muscle, although this is an uncommon feature of Horner’s syndrome.
The orbitalis muscle spans the inferior orbital fissure and helps maintain the forward position of orbital contents.
The commonest cause for Horner’s syndrome is a tumor eroding the cervicothoracic ganglion, which is typically an apical lung tumor.
Describe a surgically induced Horner’s syndrome
A surgically induced Horner’s syndrome may be necessary for patients who suffer severe hyperhidrosis (sweating). This often debilitating condition may be so severe that patients are confined to their home for fear of embarrassment. Treatment is relatively straightforward. The patient is anesthetized and a bifurcate endotracheal tube is placed into the left and right main bronchi. A small incision is made in the intercostal space on the appropriate side, and a surgically induced pneumothorax is created. The patient is ventilated through the contralateral lung.
Using an endoscope the apex of the thoracic cavity can be viewed from inside and the cervicothoracic ganglion readily identified. Obliterative techniques include thermocoagulation and surgical excision. After the ganglion has been destroyed, the endoscope is removed, the lung is reinflated, and the small hole is sutured.
How can a clinician isolate and test the functions of the superior and inferior rectus muscles
To isolate the function of and to test the superior and inferior rectus muscles, a patient is asked to track a physician’s finger laterally and then either upward or downward (Fig. 8.94B). The first movement brings the axis of the eyeball into alignment with the long axis of the superior and inferior rectus muscles. Moving the finger upward tests the superior rectus muscle and moving it downward tests the inferior rectus muscle
How can a clinician isolate and test the functions of the medial and lateral rectus muscles
To isolate the function of and test the medial and lateral rectus muscles, a patient is asked to track a physician’s finger medially and laterally, respectively, in the horizontal plane
How can a clinician isolate and test the function of the superior oblique muscle
To isolate the function of and to test the superior oblique muscle, a patient is asked to track a physician’s finger medially to bring the axis of the tendon of the muscle into alignment with the axis of the eyeball, and then to look down, which tests the muscle
How can a clinician isolate and identify the function of the inferior oblique muscle
To isolate the function of and to test the inferior oblique muscle, a patient is asked to track a physician’s finger medially to bring the axis of the eyeball into alignment with the axis of the muscle and then to look up, which tests the muscle
What does clinical examination of the eye normally involve
Examination of the eye includes assessment of the visual capabilities, the extrinsic musculature and its function, and disease processes that may affect the eye in isolation or as part of the systemic process.
Examination of the eye includes tests for visual acuity, astigmatism, visual fields, and color interpretation (to exclude color blindness) in a variety of circumstances. The physician also assesses the retina, the optic nerve and its coverings, the lens, and the cornea.
How do the extrinsic eye muscles work to produce eye movement
The extrinsic muscles work synergistically to provide appropriate and conjugate eye movement:
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lateral rectus—abducent nerve [VI],
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superior oblique—trochlear nerve [IV], and
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remainder—oculomotor nerve [III].
describe how the eye can be effected in systemic disease
The eye may be affected in systemic diseases. Diabetes mellitus typically affects the eye and may cause cataracts, macular disease, and retinal hemorrhage, all impairing vision.
Occasionally unilateral paralysis of the extra-ocular muscles occurs and is due to brainstem injury or direct nerve injury, which may be associated with tumor compression or trauma. The paralysis of a muscle is easily demonstrated when the patient attempts to move the eye in the direction associated with normal action of that muscle. Typically the patient complains of double vision (diplopia
Describe the consequences of a facial nerve palsy on the eye
Loss of innervation of the orbicularis oculi by the facial nerve [VII] causes an inability to close the eyelids tightly, allowing the lower eyelid to droop away causing spillage of tears. This loss of tears allows drying of the conjunctiva, which may ulcerate, so allowing secondary infection.
Describe the consequences of an oculomotor nerve palsy on the eye
Loss of innervation of the levator palpebrae superioris by oculomotor nerve [III] damage causes an inability of the superior eyelid to elevate, producing a ptosis. Usually, oculomotor nerve [III] damage is caused by severe head injury.
affected eye down and out with droopy eyelid (CNIV and VI unopposed so superior oblique pulls down and lateral rectus pulls out)
Describe the consequences of Horner’s syndrome on the eye
Loss of innervation of the superior tarsal muscle by sympathetic fibers causes a constant partial ptosis. Any lesion along the sympathetic trunk can induce this. An apical pulmonary malignancy should always be suspected because the ptosis may be part of Horner’s syndrome
Describe the consequences of a abducens nerve palsy on the eye
CNVI palsy: affected eye unable to abduct and deviates inwards, double vision worsens on gazing to side of affected eye
Describe the periorbita
The periosteum lining the bones that form the orbit is the periorbita (Fig. 8.87A). It is continuous at the margins of the orbit with the periosteum on the outer surface of the skull and sends extensions into the upper and lower eyelids (the orbital septa).
describe the formation of the common tendinous ring
At the various openings where the orbit communicates with the cranial cavity the periorbita is continuous with the periosteal layer of dura mater. In the posterior part of the orbit, the periorbita thickens around the optic canal and the central part of the superior orbital fissure. This is the point of origin of the four rectus muscles and is the common tendinous ring.
What is the orbital plate of the ethmoid bone also known as
The lamina papyracea- paper like layer- really thin- close contact to air cells- readily fractured
Describe a blowout fracture
Direct trauma to the eye
Increases pressure on contents inside orbit
Eyes can drop into cheeks
double vision
Where do all cranial nerves involved in extrinsic muscle function exit
The superior orbital fissure
Why does depression of the eye not isolate muscles
Both the inferior rectus and the superior oblique can depress the eye
So adduct or abduct first to isolate function
adduct first- only SO will depress then
Where is the trigeminal ganglion housed
Meckel cave- cerebrospinal fluid-containing dural pouch in the middle cranial fossa and opening from the posterior cranial fossa that houses the trigeminal ganglion.
What is a consequence of certain cranial nerves travelling through the cavernous sinus
Readily damaged by thrombosis or infection- first use of penicillin
Where is the pterygopalatine ganglion found
Behind the cheek
What is a dry eye a consequence of
PSNS issue
