The Central Visual Pathway Learning Module Click to Begin

Used with permission of the Academy of Neurologic Physical Therapy of the APTA Do not duplicate without acknowledging Learning Activity author Michael McKeough, PT, EdD

Contents Patient Cases Case 1 Case 2 Overview Introduction Learning Objectives Instructions Legend Read these Instructions! Central Visual Pathway Lesion lessons Monocular blindness Contralateral homonymous hemianopia Contralateral homonymous hemianopia with macular sparing Bitemporal hemianopia Patient Cases Case 1 Case 2 Contents Lesions Patient Cases Exit

Overview Introduction Learning Objectives Instructions Legend Contents Lesions Patient Cases Exit

Introduction This module reviews the central pathway of the visual sensory system. Module organization consists of three components. Overview of the central visual pathway, 4 interactive lesion lessons with feedback, and 2 interactive cases with feedback. At the bottom of each page, a navigation bar contains options to move throughout the module. Material is presented at both the behavioral level and the neuroanatomical level. The behavioral level is presented first and depicts a patient’s clinical presentation. The neuroanatomical level depicts the detailed anatomy of first-order, second-order and third-order neurons. The neuroanatomical level accounts for the patient’s behavioral presentation on examination under normal and lesioned conditions. Contents Lesions Patient Cases Exit

Learning Objectives After completing this module you should be able to: describe the normal structure and function of the central visual pathway. describe the signs and symptoms caused by various lesions of the central visual pathway. given a patient case (examination results and chief complaint), identify the lesion causing the symptoms. given a lesion, identify the signs and symptoms that would be expected on examination. correlate neurology information between the level of visual image and central visual pathway. Contents Lesions Patient Cases Exit

Instructions This module contains 4 interactive lesion lessons with animation. Lesson lessons begin with a question about the symptoms produced by that particular lesion. Clicking the answer button will reveal the answer to the question. Clicking the explanation button will lead to both behavioral and neuroanatomical explanations of the lesion. Each presentation is launched by clicking the animation button. The same button serves to replay the animation if desired. Please refer to the Legend that defines the symbols used throughout the module. Contents Lesions Patient Cases Exit

Legend Mechanism of injury First-order neuron Lesion Second-order neuron Sensory stimulus Third-order neuron Function intact Visual impairment Function lost Contents Lesions Patient Cases Exit

Normal Vision Click to animate The visual sensory system is crossed such that images from the left visual field are perceived in the right visual cortex and images from the right visual field are perceived in the left visual cortex. Information from the temporal hemi retina is projected to the ipsilateral visual cortex. Information from the nasal hemi retina decussates in the optic chiasm and is projected to the contralateral visual cortex. Visual Fields Left Right L R First-order neuron Second-order neuron Third-order neuron Stimulus L R Contents Lesions Patient Cases Exit

Lesion Lessons Monocular blindness Contralateral homonymous hemianopia Contralateral homonymous hemianopia with macular sparing Bitemporal hemianopia Contents Lesions Patient Cases Exit

Lesion of the right optic nerve produces what impairment? Click for answer Right monocular blindness. Damage to the right optic nerve interrupts all input from the right eye (nasal and temporal hemi retinas). Click for explanation Contents Lesions Patient Cases Exit

Monocular Blindness Normal Vision R L Visual Fields Click to animate R L Visual Fields Damage to the central visual pathway, anterior to the optic chiasm, will cause the complete loss of vision from the affected eye. Vision in the unaffected eye remains intact. Left Right Lesion Lost function Impairment L R Contents Lesions Patient Cases Exit

Lesion of the left optic tract produces what impairment? Click for answer Right homonymous hemianopia. Damage to the left optic tract interrupts input that originated in the right visual field of both eyes (left temporal hemi retina and right nasal hemi retina). Information from the left temporal hemi retina remained uncrossed while information from the right nasal hemi retina crossed in the optic chiasm. Click for explanation Contents Lesions Patient Cases Exit

Contralateral Homonymous Hemianopia Normal Vision Click to animate L R Visual Fields Damage to the central visual pathway, posterior to the optic chiasm, will cause the loss of vision from half of the visual field in each eye. The vision loss occurs in the field opposite the lesion. Left Right Lesion Lost function Impairment L R Contents Lesions Patient Cases Exit

Lesion of the left primary visual cortex produces what impairment? Click for answer Right homonymous hemianopia with macular sparing. Damage to the left primary visual cortex interrupts input that originated in the right visual field of both eyes (left temporal hemi retina and right nasal hemi retina). Cortical lesions spare information originating in the macula lutea because of the abundant cortical representation of information originating from this region of the retina. Click for explanation Contents Lesions Patient Cases Exit

Contralateral Homonymous Hemianopia (Macular sparing) Normal Vision Click to animate L R Lesion of the occipital cortex may produce macular-sparing homonymous hemianopia. This condition is most often seen in cerebrovascular accident involving the posterior cerebral artery Visual Fields Left Right Lesion Lost function Impairment L R Contents Lesions Patient Cases Exit

Lesion of the crossing fibers of the optic chiasm produces what impairment? Click for answer Bitemporal hemianopia. Damage to the crossing fibers of the optic chiasm interrupts fibers from the nasal hemi retina of both eyes. The nasal hemi retina relays information that originated from the outer visual field. Click for explanation Contents Lesions Patient Cases Exit

Bitemporal Hemianopia Normal Vision Click to animate L R Damage to center of the optic chiasm, causes the loss of vision from the lateral half of the visual field in each eye. Images from the temporal (outer) half of each visual field fall onto the nasal hemi retinas, decussate in the optic chiasm, and project to the contralateral visual cortex. Visual Fields Left Right Lesion Lost function Impairment L R Contents Lesions Patient Cases Exit

Patient Cases Read these instructions! Patient Case 1 Patient Case 2 Contents Lesions Patient Cases Exit

Case Instructions These patient cases are intended to facilitate the integration and clinical application of information about the Central Visual Pathway by coupling the findings on examination and patient interview with their neuroanatomical correlates. Each case begins with the patient’s history. Then, the question is asked about the behavioral deficits and underlying neurologic damage. Clicking the Answer button will reveal the answer and clicking the Show lesion button will reveal the neuroanatomic lesion along with the patient’s visual impairments. Cases are presented from two perspectives. What lesion would account for a given set of examination results and patient history? For a given lesion, what signs and symptoms would be expected on examination? Click on a Case number to begin the exercise. Contents Lesions Patient Cases Exit

Case 1 In the accident report, the driver of the Ford Explorer states that when she entered the intersection, she never saw the Mazda Miata coming from her right. Witnesses report that the Miata was clearly in the intersection first. The driver has a recent history of bumping into things on her right and difficulty findings things located on her right. Following the accident, the medical examination reveales that the woman is unable to see objects in the right half of both visual fields. Damage to what system(s) is causing this patient’s problems? The woman has right homonymous hemianopia. Right homonymous hemianopia is causes by damage to the central visual pathway on the left posterior to the optic chiasm (optic tract or optic radiation fibers). Images from the right half of the left visual field fall onto the temporal hemiretina of the left eye and project to the ipsilateral visual cortex via the left optic nerve, chiasm, tract, and radiation fibers. Images from the right half of the right visual field fall onto the nasal hemiretina of the right eye and project to the contralateral visual cortex via the right optic nerve, chiasm, and left optic tract and radiation fibers. Damage to the left optic tract will interrupt the image from the right half of both visual fields. Stroke involving the deep penetrating branches of the middle cerebral artery that supply the optic chiasm and optic tract is a common cause of contralateral hemianopia. Answer Show lesion Contents Lesions Patient Cases Exit

Contralateral Homonymous Hemianopia Normal Vision Click to animate L R Visual Fields Damage to the central visual pathway, posterior to the optic chiasm, will cause the loss of vision from half of the visual field in each eye. The vision loss occurs in the field opposite the lesion. Left Right Lesion Lost function Impairment L R Contents Lesions Patient Cases Exit

Case 2 Surgical report: a 1.4 cm meningioma was successfully resected from the base of the patient’s pituitary gland. Total resection required sectioning the crossing fibers of the optic chiasm. The patient is resting quietly in recovery. What signs and symptoms would be expected from this surgery? Answer Sectioning the crossing fibers of the optic chiasm would produce bitemporal hemianopia. Images from the lateral half of each visual field fall onto the nasal hemiretins, decussate in the optic chiasm, and project to the contralateral visual cortex. The surgery interrupted these fibers as they crossed in the optic chiasm thereby producing the hemianopia. Show lesion Contents Lesions Patient Cases Exit

Bitemporal Hemianopia Normal Vision Click to animate L R Damage to center of the optic chiasm, causes the loss of vision from the lateral half of the visual field in each eye. Images from the temporal (outer) half of each visual field fall onto the nasal hemi retinas, decussate in the optic chiasm, and project to the contralateral visual cortex. Visual Fields Left Right Lesion Lost function Impairment L R Contents Lesions Patient Cases Exit

D. Michael McKeough, PT, EdD The End D. Michael McKeough, PT, EdD  2015