42

42 CASE 42


A 27-year-old man is brought to the emergency department after having been involved in a motor vehicle collision.


The patient indicates that he was stopped at a stop sign and pulled into an intersection before he was hit broadside by another car that had the right of way. There is no prior history for seizures. The patient does not wear prescriptive lenses nor does he have a history of visual problems. He is currently taking topiramate (Topamax) for migraines and eszopiclone (Lunesta) for insomnia brought on because of stress.



PHYSICAL EXAMINATION



VS: T 37°C, P 90/min, R 28/min, BP 135/85 mm Hg

PE: No apparent head trauma from the collision. Reflexes were normal. Goldmann field examination shows that central vision is intact but peripheral vision is missing bilaterally.


LABORATORY STUDIES


MRI: Intracranial tumor near the optic chiasm



DIAGNOSIS


Bitemporal hemianopsia



PATHOPHYSIOLOGY OF KEY SYMPTOMS


Visual field deficits accompany many neurologic disorders. Localization of the deficit to the visual field of only one eye indicates a problem with the retinal receptors or the optic nerve of that eye. Localization of the deficit to homologous (comparable) portions of the visual fields of both eyes indicates a problem after the inputs have joined after the optic chiasm (optic tract, optic radiations, or visual cortex). Loss of vision on the temporal sides of the visual fields of both eyes (bitemporal hemianopsia) is indicative of a problem at the optic chiasm.


Lateral representation within the visual system is complex and depends on the location in the visual pathway. As an individual looks straight ahead in the environment, objects to the left of midline are in the left visual space and objects to the right of midline are in right visual space. Objects in left visual space are sensed by the receptors located on the nasal side of the left eye and also by receptors on the temporal side of the right eye. A similar pattern holds for objects in the right visual space, which are refracted by the lens of the eye on the nasal side of the right eye and the temporal side of the left eye (Fig. 42-1).


image

FIGURE 42–1 Visual pathways.


(From Jarvis C: Physical Examination and Health Assessment, 4th ed. Philadelphia, Saunders, 2004.)

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 42

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