Prosopagnosia, also called face blindness, is an inability to recognize familiar people's faces.
Prosopagnosia patients are usually unable to recognize the faces of family members, partners, or friends. In some cases, people with face blindness are unable to recognize themselves in the mirror or photos.
People who have face blindness often cope using strategies to recognize people with things they may be able to “see” or notice, such as:
- Facial expressions
- How someone walks
- Hairstyles
- Clothing
- Body shape
- Distinctive jewelry
- Scent
- Voice
- Context
For example, a prosopagnosia patient may note identifying features of someone, such as height, hair or eye color, or a mole, in order to help them identify a person.
However, sometimes these cues rely on context, such as always seeing a person in the same cubicle at an office, or the same desk in a classroom, so it can be difficult for a person with face blindness to recognize someone out of context.
What Are Symptoms of Prosopagnosia?
Symptoms of prosopagnosia (face blindness) may include:
- Inability to recognize familiar people
- Inability to recognize themselves in a mirror or in photos
- Inability to recognize certain facial expressions
- Inability to follow a person’s gaze
- Difficulty navigating
- Problems processing distance or angles
- Difficulty recognizing objects, such as cars, places, or landmarks
- Difficulty following films, television shows, or plays due to inability to recognize characters
- Psychological impact
- Worry about appearing rude when they don’t recognize someone
- Fear of social situations
- Avoiding social interactions
- Social anxiety disorder
- Difficulty forming relationships
- Depression
- Feelings of alienation
What Causes Prosopagnosia?
There are two types of prosopagnosia (face blindness), with different causes.
- Developmental prosopagnosia occurs when a person has prosopagnosia without brain damage
- Most of these people fail to develop the ability to recognize faces
- A person born with the condition may not realize they have a problem
- May have a genetic component and run within families
- Acquired prosopagnosia is a condition in which a person develops prosopagnosia after brain damage, often following a stroke or head injury
- Rare
- People who acquire the condition will notice right away they have lost the ability to recognize people they know
Prosopagnosia is not related to memory problems, learning disabilities, or vision loss. It may be associated with other developmental disorders, such as autism spectrum disorder, Turner syndrome, and Williams syndrome.
How Is Prosopagnosia Diagnosed?
Prosopagnosia (face blindness) is diagnosed with a patient history of symptoms, such as problems recognizing faces. If prosopagnosia is suspected, patients are usually referred toa neurologist for further testing.
A neurologist will assess the ability to recognize faces, read emotional cues, and determine personal characteristics such as age and sex. Tests used to help diagnose prosopagnosia include:
- The Benton Facial Recognition Test
- The Warrington Recognition Memory for Faces
- The Cambridge Face Perception Test
- The Cambridge Face Memory Test
What Is the Treatment for Prosopagnosia?
There is no cure or specific treatment for prosopagnosia (face blindness) and treatment focuses on compensatory strategies that can help people work around the condition.
Compensatory strategies to help recognize people may include learning to recognize a person's voice, clothing, or the way they walk.
Counseling may also be needed for feelings of anxiety or depression that may accompany having face blindness.
From 
Brain and Nervous System Resources
https://www.nhs.uk/conditions/face-blindness/
https://www.pnas.org/doi/10.1073/pnas.1735530100
https://www.baptisthealth.com/services/neurology-care/conditions/prosopagnosia