Disorders affecting the occipital lobe of the brain, which is almost entirely devoted to visual function
Varies, depending on the many different causes of occipital involvement
Varied, depending on the many different causes of occipital involvement
• Common causes
– Cerebral infarction
• Rarer causes
– Posterior reversible encephalopathy syndrome (PRES)
– Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS)
– Visual variant of Alzheimer’s disease
– Heidenhain variant of Creutzfeldt–Jakob disease
– Progressive multifocal leukoencephalopathy
• Visual blurring on one side of space or if bilateral on both sides of space. Patients may mistakenly believe that it is only blurred in the eye on the side of the visual defect (if they have not occluded one eye to test it).
• Unilateral lesions are occasionally asymptomatic until noted on routine examination.
• Difficulty with locating objects in environment
• Difficulty with identifying colors (Color Agnosia).
• Visual hallucinations
– Phosphenes, photopsias
– Formed hallucinations
• Visual illusions—inaccurately seeing objects
• Difficulties with reading and writing
• Less commonly
– Diplopia, polyopia, palinopsia
– Agnosias—difficulty in identifying objects despite being able to see them
• Homonymous hemianopsia
– Macular sparing may occur
– Sometimes sparing the 60–90° region in the temporal visual field (VF) in the contralateral eye
– Most often congruous
– Homonymous, congruous central scotomas with occipital tip lesions
• Homonymous quadrantanopsia
• Rarely, a unilateral a contralateral temporal crescent defect between 60 and 90° in the VF with the most anterior occipital lobe lesions
• With bilateral lesions:
– Bilateral homonymous hemianopic defects
– Cortical blindness (or cerebral blindness)
• Cortical blindness
– Normal ocular examination
– Normal pupillary reaction
– No visual response, no blink to light or visual threat
– Most often infarction or prolonged hypotension
• Anton’s syndrome
– Cortical blindness
– Patient denies blindness
– Often associated with abnormalities beyond the occipital lobe
• Dyschromatopsia or hemiachromatopsia
• Riddoch phenomenon—patient may perceive a moving object but not a stationary object.
• If occipital visual loss occurs in early life, optic atrophy and pallor may develop due to transsynaptic degeneration
DIAGNOSTIC TESTS & INTERPRETATION
• If acute, CT scan to exclude hemorrhage
• Otherwise, MRI scan
• Some patients have occipital patterns of visual loss with normal CT and MRI (e.g., trauma, Alzheimer’s). These may be detected with positron emission tomography (PET), single photon emission computed tomography (SPECT), or functional MRI (fMRI) scans.
• Lesions of optic tract and parietal and temporal lobe may have similar visual field defects.
– Other neurologic findings (e.g., aphasia, sensory loss) usually provide localizing value in these cases.
• Patients with cortical blindness may mistakenly be diagnosed with functional visual loss.
Treat underlying etiology.
• Occupational therapy
– Strategies for reading
• Saccadic and visual field training
– These therapies likely help visual function by training the patient to make eye movements toward the VF defect or shift attention to the side of the VF deficit.
• IV or IA thrombolysis for acute infarct
• Neurosurgery for mass lesions
• Radiation for tumors
• Intra-arterial therapy for arteriovenous malformations (AVMs).
• For infarct—make sure that vitals and metabolic status are stable. Consider thrombolysis if within hours of onset. Consider anticoagulation if high risk for recurrence (e.g., cardiac embolic source).
• For hemorrhage or tumor—stabilize vital signs and monitor and treat for clinically significant mass effect.
• If deficit is acute infarct or hemorrhage
• If there is significant mass effect from a structural lesion
• Varied, depending on etiology
• Counseling the ability to drive
– Regulations vary by state and country.
• Zhang X, Kedar S, Lynn MJ, et al. Homonymous hemianopia in stroke. J Neuroophthalmol 2006;26(3):180–183.
438.7 Disturbances of vision
• Isolated hemianopic defects without other neurologic findings are almost always due to an occipital lesion.
• Patients with hemianopsia may mistakenly believe that the visual loss is only in one eye until it is shown to them by occluding each eye individually.