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Prosopagnosia: an introduction or today's eye care providers.

It has been estimated that around 23% of the population have significant difficulties with facial recognition. In addition, a small number experience distortions and hallucinations, pain or discomfort, intermittent scotoma, sequencing and mapping problems, and temporal processing difficulties together with communication and anxiety responses. It may be a developmental difficulty or due to trauma eg stroke. In this introduction to optometric assessment and management of congenital prosopagnosia, and related conditions, the continuum of symptoms will be described and the effects of optometric interventions discussed. This article will present a new paradigm since eye care practitioners perhaps currently only use text when prescribing spectacles, whereas prosopagnosia relates to difficulties with facial recognition, which is very unlike reading text.

What is prosopagnosia?

Prosopagnosia is typically used as a synonym for "face blindness" ie acuity and optometric measurements are normal but the patient literally cannot see faces. This is only one presentation of facial recognition anomalies; there is a range of difficulties associated with how visual information is processed with regard to faces and their expressions. Other forms of agnosia and visual processing disorders may also be comorbid, often causing dramatic effects on quality of life. It is often found in people on the autistic spectrum but it can be found widely in the general population (symptoms include difficulty with faces/names) if appropriate testing is undertaken. The degree of disability it causes varies considerably, depending on the extent of the processing problem and ability of the patient to respond.

Development of facial recognition

Recognition of faces and facial expression is learnt but it does require a predisposed neurological processing system. For most people, the first person's face that is recognised is their mother's. This is learned through positions of features, the relationship between emotion and expression, the subtle differences in shape and position, movement and contour. In fact, humans usually have an innate ability to learn to recognise face shape and expression whatever the orientation and size of the person being viewed. For most people it is vital that this is achieved accurately, as the effects of poor facial processing can be catastrophic.


Faces can be recognised either as a whole or by scanning and building up the information into a coherent picture. It is believed that the fusiform gyrus is particularly important in processing of this information but it is likely that other areas of the brain are also involved. Expression recognition and emotion recognition problems may be associated with deficits in these areas (Figure 1), whilst deficits within the amygdala may also be responsible; the latter, however, is not accepted universally.

The effects of poor facial recognition

Normal facial recognition processes allow individuals to recognise their own faces along with those of their family and friends. In those people that have difficulty in processing faces, this ability may be impaired or even non-existent. This causes problems with self-knowledge, communication and relationships. Anxiety and fear are normal in these cases, often to a marked degree. Schooling, the ability to travel and get around, and everyday work may present significant problems. Psychosis may be suspected and anti-psychotic medications are often prescribed.

Assessment and intervention

Currently assessment is by reporting symptoms (or a lack of reported symptoms!). This means that those that are incapable or unwilling to volunteer information are assumed not to have a problem. This is probably not true in many cases. Most children with facial recognition/processing problems will learn quickly that they will be criticised if they do report symptoms and therefore facial processing deficits are rarely found unless they are specifically addressed in questioning. Sometimes photographs/ cartoons have been used to assess facial/ emotion recognition problems in autistic spectrum disorders (ASD) but they have the disadvantage that they are not three-dimensional and cannot move. There is anecdotal evidence that three-dimensional vision may be impaired and that movement may play a part in recognition problems for some.



There is no standard method of screening or assessment for facial/ emotion recognition difficulties. The author in his specialist practice has therefore developed a new technique of screening which appears to work extremely well. The child is directed to look at the nose of the examiner and to state how much of the face they can see clearly without moving their eyes. The practitioner can watch for scanning eye movements and in an ideal world the eyes and mouth will be reported to be clear. What is often reported in those with facial/emotion recognition difficulties may actually be quite surprising! For example, patients may report multiple features or faces appearing monster-like. The face is then rotated quickly and the subject is asked if there is any change to the appearance. Normally slight blurring may be expected but some of the reported changes can be very strange, eg the face may appear to move in stages giving the appearance of multiple still pictures that are superimposed.

Where atypical responses are given, a clinical assessment is conducted using the Orthoscopics Read Eye (Orthoscopics, Cambridge, UK), which is the only instrument available that has the range and capabilities necessary to modify facial feature recognition using colour. This instrument can be used to determine the precise range within colour space in which facial/feature recognition becomes stable and optimised, in a process that is akin to the use of coloured filters for reading difficulties. It is possible to assess the effects of varying lighting conditions accurately (to precise International CIE coordinate standards) and prescribe lenses appropriately.

The typical reading assessment techniques are not appropriate for this condition, as the effect is often only found when viewing faces (and the filter may be different in facial recognition problems from that used when reading). It is generally essential that specialist band filters be prescribed as broadspectrum filters are usually inadequate and are usually inappropriate in profound cases. The lenses often have to be "tuned" and prescribed extremely accurately to extremely high tolerance levels. This technique appears to be an extremely successful method of intervention with 100% improvement and cessation of symptoms reported to date. However, fully controlled randomised clinical trials are needed to verify these results. Results are immediate and responses from patients are often dramatic.

Facial mapping problems

Facial recognition and expression recognition problems form a continuum of disability with a wide variety of presentations. For many patients provocation of symptoms is possible, with the degree of difficulty depending on stimulus. Therefore symptoms may change depending on the visual environment. Other sensory inputs may also be important in the overall condition and it is critical that the eye care professional is sensitive to other factors. In many patients, more than one area of difficulty with processing of facial features may be present and will require addressing. To simplify the range of problems that may be encountered on a daily basis, the symptoms can be differentiated into discrete groups as discussed in the next few sections.

Three-dimensional contours

The patient will report either a reduction or an increase in contours within the face. This can make the judgement of a person's age very unreliable. Patients report faces being "cartoon-like" or people "looking like gremlins". Wrinkles may be described as pronounced and in extreme cases they can be very frightening. Analysis of emotion may be skewed as expression relies heavily on facial contours. Mimicry can be poor and those patients with this problem will often have a flat facial expression.

Peripheral blurring

When looking at the nose of an individual, the individual may only see the tip of the nose clearly, with the rest of the face being blurred (Figure 2). To recognise the face or expression, they may have to scan the face and build-up the expression internally. This is often inaccurate. The person may learn to recognise people from a small part of the facial area only eg the teeth or hair but this can cause significant problems if there is a change, for example after a haircut! Context will provide clues, but these can be misleading.


For many people, parts of the face may disappear completely from the full visage to a quadrant or half the face disappearing (Figure 3). The most common facial disappearances are: upper field, lower field, right or left field. In addition, individual features may disappear. In some cases the patients report the face will disappear but the expression/features may appear in empty space adjacent to the person viewed. Alternatively multiple features may become apparent, with four eyes commonly reported.


Metamorphosis is reported frequently. Faces (or parts of faces) will often become geometric shapes, colours may change and in extreme cases the face (or part of the face) may appear to become that of a face of a different animal eg a spider or a hamster. In rare cases the face may become monster-like. The size of the face or parts of the face may become grossly distorted (Figure 4). Sometimes the face becomes twisted, elongated and vibrates. Rarely it appears to turn upside down. Metamorphosis can be extremely disturbing and upsetting for a child.




There may be desynchronisation of speech sounds with the movement of the mouth. This can result in difficulties with auditory processing due to the McGurk effect. (1) In rare cases the mouth may appear to spin rather than open and close. This can also impact on auditory processing. Timing synchronisation using the Orthoscopics Read Eye is possible and symptom alleviation is instantaneous.


The relative position of parts of the face may appear to be incorrect, eg the mouth may appear to be positioned on the forehead (Figure 5). The sizes of the eyes, mouth and nose may be disproportionate and vary depending on the viewing angle. A common effect is to see the eyes low on the cheeks.

Movement effects

For some children facial stability may be dependent on whether the face viewed is moving or still, and this may vary depending on the stimulus. Under certain ambient light conditions, the face may appear to be stable when it is still, and unstable when it is moving, whilst in other ambient light conditions this may be reversed. The challenge is to find a coloured filtered lens that will work in both conditions, which can be difficult and often requires a great deal of skill and knowledge.

Binocular vision effects

Unusual binocular vision effects when viewing faces may sometimes be found, including variable facial (visual) fields eg perceived hemianopias, which are only apparent in certain positions of gaze. Muscle anomalies and fusion difficulties are common. Although the standard procedure would be to address these first, this must be questioned since treating visual processing symptoms can result in immediate resolution of binocular vision problems. Further research is necessary as to the cause and effect.


Visual persistence is very common, either monocularly or binocularly, in those that have difficulties with processing faces. Faces may appear in two places at the same time but the images are not processed simultaneously. This can be very disturbing and may be diagnosed as hallucinations or schizophrenia. Faces may appear to be superimposed on the next image seen or appear to leave a trail during movement. Multiple images may also be seen.

Other symptoms

Other facial recognition problems such as emotional response abnormalities, eg Capgrass Syndrome, are rare but may be encountered. Attentional difficulties are commonly found and there is a myriad of comorbidities that may be encountered eg synesthesia, sensory integration problems, and auditory processing deficits.

Emotional responses

The impact of facial recognition problems can be profound. Anxiety, fear, apparent phobias and school difficulties are common. Relationships and communication are often severely affected. Depression is also common whilst anger is often a secondary response; "Why was this not addressed earlier by professionals?"


Children with facial recognition problems have a greatly increased risk of being bullied because they cannot recognise danger signals. They may be more likely to go off with a stranger, as they cannot recognise faces. The school journey can also be a problem.

The role of the eye care professional

The first role of the eye care professional is to recognise when a problem is present. It should be assumed that children on the autistic spectrum have a high-risk level, with intermediate risk in those with dyspraxia and communication problems. A poor memory of faces and/or names may indicate problems. Those with agoraphobia, panic attacks and social difficulties should be considered as possible patients that require screening. Children with school phobia, or who are regular truants or exhibit anti-social behaviour may also have problems. Occasionally the facial expression of the patient may provide a clue. Appropriate questioning will determine the extent of problem.

Once the eye care professional is aware of the problem, they have a duty to either address it or refer to someone who has the appropriate instrumentation and knowledge. Of course optometrists may continue to follow the current paradigm, which will lead to the problem not being addressed. Indeed, addressing visual processing problems requires a completely new set of skills, and practitioners will need to be able to use their professional judgement on many occasions for individuals with complex symptoms. The challenge is substantial, with visual processing disorders being very common, yet rarely addressed by the optical and medical professions. Prosopagnosia responds extremely well to optometric intervention and therefore it seems reasonable to expect optometrists to address this problem in the future.


(1.) Green K. P. & Gerdeman A. (1995). Cross-modal discrepancies in coarticulation and the integration of speech information: the McGurk effect with mismatched vowels. Journal of Experimental Psychology Human Perception and Performance 21;1409-26.

Ian Jordan is a dispensing optician working with his optometrist wife in their specialist practice in Ayr, Scotland. He is a director in Orthoscopics and is heavily involved with research and development.
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Author:Jordan, Ian
Publication:Optometry Today
Geographic Code:4EUUK
Date:Dec 4, 2009
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