Hemianopsia

Hemianopsia is a loss of vision in one-half of the normal visual field (usually the right or left half) of one or both eyes. However, if the visual field defects are identical in both eyes but affect less than one-half of the field of vision in each eye (incomplete homonymous hemianopsia), the lesion may be in the occipital lobe; otherwise, it probably involves the parietal or temporal lobe. (See Recognizing types of hemianopsia, page 320.)

Hemianopsia is caused by a lesion affecting the optic chiasm, tract, or radiation. Defects in visual perception due to cerebral lesions are usually associated with impaired color vision.

History and physical examination

Suspect a visual field defect if the patient seems startled when you approach him from one side or if he fails to see objects placed directly in front of him. To help determine the type of defect, compare the patient's visual fields with your own—assuming that yours are normal. First, ask the patient to cover his right eye while you cover your left eye. Then move a pen or similarly shaped object from the periphery of his (and your) uncovered eye into his field of vision. Ask the patient to indicate when he first sees the object. Does he see it at the same time you do? After you do? Repeat this test in each quadrant of both eyes. Then, for each eye, plot the defect by shading the area of a circle that corresponds to the area of vision loss.

Next, evaluate the patient's level of consciousness (LOC), take his vital signs, and check his pupillary reaction and motor response. Ask if he has recently experienced a headache, dysarthria, or seizures. Does he have ptosis or facial or extremity weakness? Hallucinations or loss of color vision? When did neurologic symptoms start? Obtain a medical history, noting especially eye disorders, hypertension, diabetes mellitus, and recent head trauma.

Medical causes

Carotid artery aneurysm.An aneurysm in the internal carotid artery can cause contralateral or bilateral defects in the visual fields. It can also cause hemiplegia, a decreased LOC, a headache, aphasia, behavior disturbances, and unilateral hypoesthesia.

Occipital lobe lesion.The most common symptoms arising from a lesion of one occipital lobe are incomplete homonymous hemianopsia, scotomas, and impaired color vision. The patient may also experience visual hallucinations—flashes of light or color or visions of objects, people, animals, or geometric forms. These may appear in the defective field or may move toward it from the intact field.

Parietal lobe lesion.Parietal lobe lesion produces homonymous hemianopsia and sensory deficits, such as an inability to perceive body position or passive movement or to localize tactile, thermal, or vibratory stimuli. It may also cause apraxia and visual or tactile agnosia.

Pituitary tumor.A tumor that compresses nerve fibers supplying the nasal half of both retinas causes complete or partial bitemporal hemianopsia that first occurs in the upper visual fields but later can progress to blindness. Related findings include blurred vision, diplopia, a headache and, rarely, somnolence, hypothermia, and seizures.

Stroke.Hemianopsia can result when a hemorrhagic, thrombotic, or embolic stroke affects part of the optic pathway. Associated signs and symptoms vary according to the location and size of the stroke, but may include a decreased LOC; intellectual deficits, such as memory loss and poor judgment; personality changes; emotional lability; a headache; and seizures. The patient may also develop contralateral hemiplegia, dysarthria, dysphagia, ataxia, a unilateral sensory loss, apraxia, agnosia, aphasia, blurred vision, decreased visual acuity, and diplopia. He may also experience urine retention or incontinence, constipation, and vomiting.

Nursing considerations

▪ If the patient's visual field defect is significant, prepare him for further testing, such as perimetry or a tangent screen examination.

▪ To avoid startling the patient, approach him from the unaffected side and position his bed so that his unaffected side faces the door.

▪ If he's ambulatory, remove objects that could cause falls and alert him to other possible hazards.

▪ Place his clock and other personal objects within his field of vision, and avoid putting dangerous objects (such as hot dishes) where he can't see them.

Patient teaching

▪ Explain the extent of the defect to the patient so that he can learn to compensate for it.

▪ Advise him to scan his surroundings frequently, turning his head in the direction of the defective visual field.

▪ Discuss safety measures that may be needed.

Pictures

Book Source Details

• Book Title: Nursing: Interpreting Signs and Symptoms
• Author(s): Springhouse
• Year of Publication: 2007
• Copyright Details: Nursing: Interpreting Signs and Symptoms, Copyright © 2007 Lippincott Williams & Wilkins.

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Copyright Details: Nursing: Interpreting Signs and Symptoms, Copyright © 2008 Williams & Wilkins.

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More About This Book: Title: Nursing: Interpreting Signs and Symptoms Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 1-58255-668-7

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