A 67-year-old woman comes to the clinic due to decreased vision in her right eye that she noticed a week ago. The patient says that her sight in the right eye is "narrower" than in the left. Her past medical history is significant for hypertension, type 2 diabetes mellitus, and hyperlipidemia. She also suffers from intermittent lower limb claudication and has had 2 prior episodes of transient vision loss in her right eye. Visual field testing reveals a right nasal hemianopia. MRI/magnetic resonance angiography of the head and neck reveal a right internal carotid artery aneurysm. Which of the following portions of the visual pathway is most likely disrupted in this patient?

Question

A 67-year-old woman comes to the clinic due to decreased vision in her right eye that she noticed a week ago.  The patient says that her sight in the right eye is "narrower" than in the left.  Her past medical history is significant for hypertension, type 2 diabetes mellitus, and hyperlipidemia.  She also suffers from intermittent lower limb claudication and has had 2 prior episodes of transient vision loss in her right eye.  Visual field testing reveals a right nasal hemianopia.  MRI/magnetic resonance angiography of the head and neck reveal a right internal carotid artery aneurysm.  Which of the following portions of the visual pathway is most likely disrupted in this patient?

Quizplus · Accepted Answer

11ec160b_35d4_270c_9249_8325c57cd2bb_MD0001_00 Humans have a maximum horizontal field of view of about 200 degrees with both eyes. The central 120 degrees make up the binocular field of view (stereoscopic vision), with 2 side fields of about 40 degrees seen by only 1 eye (monoscopic vision). Unilateral visual defects within the binocular field of view (such as unilateral nasal hemianopia) may be masked due to compensation by the normal eye and may go unnoticed by the patient. Light from the nasal visual field strikes the temporal side of each retina, and optic nerve fibers from the temporal part of the retina travel laterally through the optic chiasm to pass into the ipsilateral optic tract. Lesions involving the lateral aspects of the optic chiasm can cause ipsilateral nasal hemianopia by damaging these uncrossed, temporal retinal fibers. This may occur with aneurysm of the internal carotid artery (eg, cavernous or ophthalmic segments), as seen in this patient. (Choice A) A partial lesion involving the retina is more likely to produce focal monocular scotoma than nasal hemianopia as a lesion with the latter would need to involve the entire temporal hemiretina. Educational objective: An aneurysm of the internal carotid artery can laterally impinge on the optic chiasm. This can cause ipsilateral nasal hemianopia by damaging uncrossed optic nerve fibers from the temporal portion of the retina. __________ References: Unilateral nasal hemianopia as a sign of intracranial optic nerve compression. (http://www.ncbi.nlm.nih.gov/pubmed/7270639) Giant aneurysms of the carotid system presenting as visual field defect. (http://www.ncbi.nlm.nih.gov/pubmed/7217950)

A 67-Year-Old Woman Comes to the Clinic Due to Decreased