Prosopagnosia

Prosopagnosia, or face blindness is a brain disorder and is characterized by the impairment in the recognition of facial identity. It is a neuro-ophthalmic cognitive disorder of face perception in which the ability to recognize family members, spouses, close friends, and even one's own face (self-recognition), is impaired.
It can also affect a person's ability to recognise objects, such as places or cars.
Some people with prosopagnosia cannot recognise certain facial expressions, judge a person's age or gender, or follow a person's gaze.
Prosopagnosia is defined by problems recognizing faces, not recalling names.
People with face blindness have normal visual acuity and other aspects of visual processing such as object discrimination and decision-making (intellectual functioning) remain intact.
They can differentiate between shades of colors, identify patterns, and see in 3D as well. They do not have any problems with memory or interpretation and have normal intelligence.
About 2 percent of the population suffer from prosopagnosia.
The right hemisphere of the brain is more important for face recognition.
Areas of face recognition are also present in the left hemisphere. All these areas are interconnected, and all become active when faces are viewed.
A number of different processes are involved in face processing in the normal brain.
The area in the brain, that plays an important role in coordinating the neural systems that affect facial memory and perception, is a fold in the brain called the right fusiform gyrus.
The temporal lobe of the brain is partly responsible for the ability to recognize faces. Some neurons in the temporal lobe respond to particular features of faces.
Prosopagnosia results from problems in the face network.
As the face seems to function as an important identifying feature in memory, it can also be difficult for people with prosopagnosia to keep track of information about people, and socialize normally with others. So, they depend upon secondary clues such as clothing, gait, hair color, skin color, body shape, and voice.

Prosopagnosia, or face blindness may be congenital or acquired.
Congenital prosopagnosia (CP), also called Developmental prosopagnosia (DP) appears in early childhood, and remains lifelong. Many people do not realize that they have DP until later in their adult lives. Congenital prosopagnosia may be hereditary or genetic.
The analysis of pedigree trees indicates that hereditary prosopagnosia (HPA) is autosomal dominant inheritance.
Acquired prosopagnosia is generally found in adults and is due to the damage to the occipito-temporal lobe of the brain. It can also result from stroke, traumatic brain injury, or certain neurodegenerative diseases.

Acquired prosopagnosia may be apperceptive or associative.
Apperceptive prosopagnosia - People with this disorder are unable to recognize both familiar and unfamiliar faces and are unable to make the same–different judgments when they are presented with pictures of different faces.
Associative prosopagnosia -- People with this form of the disorder can make sense of some face information that they may be able to tell whether photos of people's faces are the same or different and derive the age and sex from a face. They may be unable to identify the person or provide any information about them such as their name, occupation, or when they were last encountered.

Clinical Features

The primary symptom of prosopagnosia is an inability to recognize persons or discriminate between faces.
Prosopagnosics also sometimes have difficulty imagining the faces of people they know.
Other clinical features of Prosopagnosia are,

inability to recognize persons by their faces
poor recognition of familiar individuals in person or in photographs.
an inability to describe faces.
confusion regarding plotlines in movies or plays with numerous characters.
feelings of disorientation in crowded locations.
difficulty distinguishing individuals wearing uniforms or similar articles of clothing
establishment of identities by asking personal questions or by focusing on significant clothing, hairstyles, jewelry, perfumes, or colognes
refusal to greet individuals by name
avoidance of meeting new people
social isolation and depression
inability to process angles or distance
problems remembering places and landmarks
may appear rude or not interested when they fail to recognise a person.

Causative factors

Congenital prosopagnosia -- people are born with face blindness may be hereditary or genetic as it runs in families
Acquired prosopagnosia may be caused by abnormalities, impairment, or damage to the right fusiform gyrus of brain
It can also be caused by stroke, injury to the brain, or some neurodegenerative diseases
cerebral infarcts and intracranial hemorrhages in the posterior cerebral circulation may cause face blindness
less common causes may be neoplastic, infectious, neurodegenerative disease, and traumatic brain injury
Other less common causes include carbon monoxide poisoning, temporal lobectomy, encephalitis, neoplasm, right temporal lobe atrophy, injury, Parkinson's disease, and Alzheimer's disease.

Diagnosis

The diagnosis of prosopagnosia is made clinically.
Currently, there is no single gold-standard diagnostic technique.
There are a few neurocognitive diagnostic tests that can be used with the assessment. They are,
The Bielefelder Famous Faces Test (BFFT) -- a test in which 70 standardized “famous” faces are shown, asked to either report who the individual is or describe the face
The Benton Facial Recognition Test,(BFRT) -- a test in which a target face versus multiple test faces is presented, and the patient is asked to match the target face with the correct test face.
The Cambridge Face Memory Test (CFMT)-- similar to BFRT and it evaluates the patient’s ability to match unfamiliar faces
The neurologist may take an assessment that evaluates the ability to recognize facial features. They may be

recognizing faces never seen, or faces of family members
noticing differences or similarities of facial features in sets of faces shown
detecting emotional cues from a set of faces
assessing information like age or gender from a set of faces

Remedial steps

Currently there is no effective cure for prosopagnosia. Several training programmes are being developed to help improve facial recognition.
Compensatory strategies such as verbalizing facial details (may help with person recognition) and techniques that attempt to restore normal face-processing mechanisms can be used.
Coping skills such as noting a person’s height, hairstyle, build, clothing, accessories, vocal mannerisms, voice, the way they walk and gait as sources of recognition can assist prosopagnosics in identifying other people
Managing social anxiety or depression symptoms
Prevention of further brain damage if possible.