Prosopagnosia, also known as face blindness, refers to the neuro-ophthalmic disorder in which a patient as difficulty perceiving or recognizing faces. Prosopagnosia is derived from Greek: proso for “face”, a for “not”, and osia for “know”. Prosopagnosia can be characterized into two types: associative and apperceptive. Apperceptive prosopagnosia is defined as the inability to even perceive and cognitively process the face. Associative prosopagnosia is defined as inability to recognize or apply any meaning to the face, despite perceiving it.
Prosopagnosia can have multiple causes; because this is a disorder of visual processing. Lesions can be further localized to inferior occipital region, fusiform gyrus, and temporal cortex. The most common causes include cerebral infarcts and intracranial hemorrhages in the posterior cerebral circulation. Other less common etiologies for cortical damage can include neoplastic, infectious, neurodegenerative disease, and traumatic brain injury.
Visual information is first received in the V1-2 visual cortex. This information then travels to the V3-5 visual association cortex. Both a ventral and dorsal stream are necessary to further interpret “what” is seen and “where” it is seen, respectively. Facial recognition is processed in the inferior occipital lobe at the fusiform gyrus, where communication occurs with the temporal lobe to associate with memory and apply meaning to the face. When there is a lesion that occurs at some level of this processing, the patient complains of prosopagnosia. Usually lesions are in the bilateral inferior occipitotemporal lobes. Unilateral cases are less common, but when they occur, they are most often attributable to right-sided lesions.
The diagnosis of prosopagnosia is made clinically. There are a few neurocognitive diagnostic tests that can be used to aid with the evaluation. The Bielefelder Famous Faces Test (BFFT) is a test in which the subject is shown 70 standardized “famous” faces, asked to either report who the individual is or describe the face. The Benton Facial Recognition Test (BFRT) is a test in which the subject is presented with a target face versus multiple test faces, and the subject is asked to match the target face with the correct test face. The Cambridge Face Memory Test (CFMT) is similar to BFRT as it also evaluates the patient’s ability to match unfamiliar faces. Because the BFRT and CFMT are both evaluating facial matching but not recognition, these tests are better served to evaluate associative prosopagnosia, as these patients are still able to perceive faces without difficulty. Additionally, free online questionnaires are available for the self-evaluation of prosopagnosia. Currently, there is no single gold-standard diagnostic technique, as these tests need further study to assess reliability.
Because there are no proven diagnostic methods, one often relies on the clinical history to help diagnose prosopagnosia. A patient with apperceptive prosopagnosia will claim they are unable to even perceive a face at all, let alone recognize who the face belongs to. They are generally able to perceive other objects. A patient with associate prosopagnosia will claim no issue perceiving a face but will not be able to attach meaning to the face. These patients tend to recognize other cues, such as voice and clothing, to recognize the individual. Additionally, an unusual type of prosopagnosia, known as “mirror-image” prosopagnosia, presents with the patient not recognizing their own face in the mirror or photographs.
Additional history can assist with understanding the etiology of the prosopagnosia. Questions to ask the patient include history of head trauma, hypertension, diabetes mellitus, coronary artery disease, prior strokes, Alzheimer disease, Parkinson disease, and current medications.
Physical exams are generally noncontributory, but the patient may have signs and symptoms that help understanding the underlying cause, such as head bruise, funduscopic findings of uncontrolled hypertension and diabetes mellitus, and Parkinsonian movements. A patient can present with intact near and distant visual acuity. However, if a patient with prosopagnosia presents with left-sided homonymous hemianopsia, there should be concern for a right-sided occipital lesion.
Currently there are no effective treatments for prosopagnosia. The standard of care for these patients is to treat their underlying condition, and prevention of further brain damage if possible. Spontaneous recovery of prosopagnosia has been rarely noted in the literature. Some evidence has been shown that compensatory treatments such as verbalizing facial details may be effective in retraining these patients to enhance facial recognition, but due to the limited evidence, this remains a controversial tool for the treatment of prosopagnosia. Low vision rehabilitation is recommended for patients with visual loss and patients with prosopagnosia might benefit from retraining strategies and methods to increase neuroplasticity.
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