22 Orbit and Eye Flashcards
An infant has a small area of the right iris missing and a diagnosis of coloboma of the iris is made. What is the embryologic cause of the coloboma?
A coloboma of the iris is caused by failure of the retinal fissure to close during the 6th week.
A patient is unable to adduct his left eye and lacks a corneal reflex on the left side. Where is the location of the lesion?
The superior orbital fissure is the opening that allows the passage of CN III, IV, VI and V-1.
The eye impairment is due to a lesion in the oculomotor nerve.
Examination of a patient reveals an inferior fracture of the orbit. Orbital structures would most likely be found inferiorly in which space?
The maxillary sinus is located directly inferior to the orbit.
The ethmoidal sinus is located superiorly and medially to the orbit, whereas the frontal sinus is located superiorly to the orbit.
A patient is hospitalized due to cavernous sinus thrombosis resulting from an infxn on her face. What is the most direct route for spread of infxn from the face to the cavernous sinus?
The superior ophthalmic vein drain directly into the cavernous sinus. The danger area of the face is located in the triangular region from the lateral angle of the eye to the middle of the upper lip, near the nose and is drained by the facial vein. The facial vein communicates directly with the cavernous sinus through the sup. ophthalmic vein.
A patient complains of diplopia when walking down stairs. A lesion of which nerve is responsible for the patient’s complaint?
The trochlear nerve innervates the sup. oblique muscle, which acts to move the pupil downward and medially. It is the only muscle that can depress the pupil when the eye is adducted.
When a patient is told to turn his right eye inward toward his nose and look down, he is able to look inward but now down. What nerve is injured?
The trochlear nerve (superior oblique muscle) turns the pupil downard from the adducted position.
The abducens innervates the lateral rectus, resulting in abduction of the eye.
During examination, it is suspected that the right abducens nerve of a patient is damaged. In which direction will the physician ask the patient to turn her right eye to confirm the abducens nerve damage?
The right abducens nerve innervates the right lateral rectus, which mediates outward movement (abduction) of the right eye. Inward movement is accomplished by the medial rectus, supplied by CN III.
A patient has partial ptosis. Which muscles are paralyzed?
The superior tarsal muscle (of Muller) is innervated by sympathetics, is smooth muscle that assists in elevating the eyelids and maintaining this position. Loss of symp. innervation will result in partial ptosis of the eyelid.
A patient has glaucoma. Which space first receives the aqueous humor secreted by the epithelium of the ciliary body?
The posterior chamber receives ciliary body secretions first. The ciliary body produces aqueous humor and is located in the posterior chamber.
A patient’s eye is fixed in an abducted position, slightly depressed and the pupil is dilated. The upper eyelid is droopy.
Which nerve is affected?
A lesion of the oculomotor nerve will cause the eye to remain in a down and out position. This is due to the actions of the unopposed lateral rectus and superior oblique.
The partial ptosis is due to paralysis of the levator palpebrae muscle. The pupil will remain dilated bc of loss of PS innervation to constrictor pupillae muscle.
What condition in the eye woudl indicate that CSF pressure is too elevated for a lumbar puncture to be performed?
Papilledema is optic disc swelling that is caused by increased intracranial pressure caused by increased CSF pressure. If a lumbar puncture is performed in a patient with elevaed CSF pressure and fluid is withdrawn from the lumbar cistern, the brain can become displaced caudally and the brainstem is pushed against the tentorial notch. This is known as brain herniation.
Radiograph reveals an aneurysm of the internal carotid artery within the cavernous sinus. During physical examination, what sign would one expect to see first if nerve compression has occurred within the cavernous sinus?
Within the cavernous sinus, the abducens nerve is in intimate contact with the ICA. This would cause ipsilateral paralysis of abduction of the pupil.
Examination reveals that the upper eyelid of a patient has multiple laceration and the sclera contains small fragments from his broken glasses. What site would be preferable for needle insertion to anesthetize the orbital contents and then the area of the eyelid injury?
It is necessary to anesthetize the conjunctival covering of the sclera which is supplied by the nasociliary branch of the ophthalmic division of the trigeminal nerve. To do this, the needle should be placed through the upper eyelid deeply toward the orbital apex to infiltrate the nascoiliary nerve and also between the orbital septum and the palpebral musculature laterally to anesthetize lateral sensory supply from the lacrimal nerve.
An infant is brought to the hospital by his parents because of white patches in his eyes. He has a congenital cataract; what condition can cause this?
Infection by teratogenic agents such as rubella virus can cause congenital cataracts.
A patient has an inferior blow-out fracture of the orbit. Which nerve is vulnerable with this type of injury?
An inferior fracture of the orbit would likely damage the infraorbital nerve. A blow-out fracture results in a displaced orbital wall, and in this case, the inferior wall. The infraorbital nerve leaves the skull immediately inferior to the inferior aspect of the orbit, via the infraorbital foramen.
A patient is asked to gaze upwards and the result is shown in the image. Imaging studies reveal a fracture. Which muscle is affected?
The CT scan shows an orbital (blow-out) fracture. The inf. rectus muscle originates from the inferior part of the common tendinous ring and inserts on the inf. ant. part of the eyeball. With an orbital fracture, an injury to the floor of the orbit results in entrapment of the inf. rectus muscle by a fragment of the bone. This tethers the inf. rectus muscle to bone resulting in loss of fxn of the muscle.
