Functional (nonorganic) visual loss is frequently encountered in ophthalmic and neurologic practice, occurring in 0.5–5% of patients presenting with vision loss. Patients with functional visual loss may be misdiagnosed because of the paucity of objective findings on examination. Identifying such patients is extremely important to avoid unnecessary laboratory testing and facilitate secondary gain. Likewise, it is imperative to be able to identify patients with organic vision loss with superimposed functional vision loss. Although the characterization of the psychological profile of patients with functional vision loss is helpful, for the ophthalmologist or neurologist, a familiarity with diagnostic strategies used to identify functional vision loss is more important. In this chapter, terminology is clarified, then patient types and their potential interactions with the examiner are described. The methods used to diagnose functional vision loss are reviewed in detail, followed by a brief description of other neuro-ophthalmologic manifestations of nonorganic disease.
Historically, numerous terms have been used to describe functional visual loss, including hysteria, hysterical visual loss, malingering, nonphysiologic visual loss, factitious visual loss, nonorganic visual loss, psychogenic visual loss, Munchausen syndrome, and conversion disorder of vision. Ambiguity results for two different reasons. First, there has been no universal agreement about a term to describe nonorganic visual loss. The term functional visual loss denotes a symptomatic and measured loss of vision that is unassociated with an identifiable lesion of the visual pathways. Furthermore, for patients with functional visual loss there is no explanation for their complaints on the basis of contemporary knowledge of the visual pathways. Thus the term functional visual loss is equivalent to factitious, nonorganic, medically unexplained, and nonphysiologic visual loss.
The second level of confusion exists when the terminology attempts to identify the underlying cause or circumstance of the nonorganicity. For instance, malingering implies that there is a willful alteration of subjective symptoms and responses on examination. Usually this is an attempt to secure secondary gain such as time away from work or monetary gain from an insurance settlement. Such patients with volitional alteration of the examination can be labeled as malingerers if the examiner chooses to begin a long and arduous confrontation with the patient, lawyers, and insurance companies. Instead, the examiner may simply report the vision loss as functional and incompatible with a specific organic lesion. This approach is particularly wise when the initial factors driving the feigned loss are unclear.
Other diagnoses, such as hysteria, conversion disorder, Munchausen syndrome, hypochondriasis, or somatization disorder, may be considered in patients who are not clearly seeking secondary gain. The use of each of these terms is dependent on an understanding of the patient’s potential psychiatric problems. For instance, Munchausen syndrome is a factitious disorder in which the patient intentionally produces physical signs and symptoms. When Munchausen syndrome is associated with visual loss, patients can have associated eyelid swelling, conjunctival injection, or hemorrhages ( Fig. 11.1 ). This may be the result of self-inflicted trauma or self-instilled eye irritant. These patients generally have some psychogenic factor driving them to assume the role of a sick person.
The physical symptoms of a patient with a conversion disorder and vision loss may reflect an inner conflict. The label conversion disorder incorporates many of the patients who, in the past, were diagnosed as having hysteria or hysterical vision loss. Hysteria derives from the root “hyst,” referring to the uterus. This terminology had its beginnings in ancient Greece, where many conditions were thought to occur only in women, and the uterus was thought to have a will of its own. Until the 19th century this was a popular notion. Charcot was the first to ascribe “hysterical symptoms” to a mental disorder, and he felt it was likely that a specific brain lesion was present in these patients. Babinski expanded on the notion that these symptoms were likely “caused by suggestion and cured by persuasion.” Freud popularized the concept that, like all else, “hysterical” vision loss had its basis in the inner unconscious battle between the ego, id, and superego. He then popularized the term conversion disorder, referring to an emotional symptom that leads to a physical finding. These patients, although less deliberate than malingerers, may realize both primary (reduction of stress from inner conflict) and secondary (more attention) gain.
Finally, hypochondriacs are patients who excessively report signs and symptoms and believe they are seriously ill. They also attempt to convince the examiner that their symptoms and problems are serious. In somatization disorders, patients who are depressed or suffering from an anxiety disorder report numerous vague complaints. These may include symptoms of vision loss that ultimately prove to be nonorganic.
Since the terminology is inexact and overlapping, the umbrella term of functional visual loss is preferable, and during the interview and examination the examiner should attempt to determine whether there is any secondary gain. It is important to understand the terminology used to identify each of the types of psychogenic illness associated with functional visual loss, but ultimately others more expert in psychiatric illness should apply the specific label. Although the techniques used to identify patients who are malingering versus those who truly have some psychogenic process are the same, the interventions or treatment required may differ immensely.
Some insight into and understanding of the types of patients with functional visual loss, as well as the attitudes of both the examiner and the patient toward their interaction, are essential. This understanding will help to make a potentially difficult interaction tolerable and nonconfrontational.
The distortion of the patient–physician relationship in this setting may be very difficult for the physician to accept and manage. Instead of using knowledge and skill to diagnose and treat a real problem, the examiner instead often becomes frustrated and confrontational as he or she becomes increasingly suspicious regarding the nature of the patient’s disorder. To paraphrase Thompson, what usually is an allied relationship between doctor and patient against the common enemy of vision loss becomes an adversarial relationship in which the patient complains of vision loss, and the physician is out to prove otherwise. Many patients in this situation become angry and frustrated because they feel the physician is not taking them seriously and is dismissive of their complaints. On the other hand, many times the physician fails to make the correct diagnosis because of this distortion in the doctor–patient relationship. More concerning is the fact that as many as half of patients with functional visual loss have this superimposed upon true or organic pathology. Any underlying problems may be unrecognized because the examiner is so put off by the patient’s behavior.
Patients with functional visual loss come from all socioeconomic groups. There is no clear sex or race predilection. A large proportion of one series consisted of blue-collar workers. Another series found a high prevalence of functional visual loss in Cambodians living in California, and the authors postulated a relationship to previous stress during incarceration in prison camps. In adults there is a high prevalence of preexisting psychiatric disorders. Although to some extent linked to the previous discussion of terminology, the types of patients encountered, along with the type of interaction they are likely to have with the examiner, have been characterized by Thompson under a slightly different scheme. He offered descriptive subgroups: the deliberate malingerer, worried impostor, impressionable exaggerator, and suggestible innocent. Characteristics of each of these patients are summarized in Table 11.1 . This schema is useful in distinguishing patients, as it avoids the term hysteria. It can assist with the interaction with the patient and can guide the examiner when giving advice to the patient, the family, and the referring doctor.
|Patient Type||Patient’s Feelings||Patient’s Behavior||Characteristics of Interaction|
|Deliberate malingerer||Malicious intent||Deliberate nonorganic responses||Confrontational; contest between patient and doctor|
|Worried impostor||Concerned that something is being missed||Aware of symptom exaggeration; self-doubt leads patient to believe symptoms||Tries to convince examiner of severity; often will accept diagnosis of “healthy eyes”|
|Impressionable exaggerator||Certain something is wrong with eyes||Does not want to hide serious problem; awareness of nonorganic symptoms is result of wanting to be sure nothing is missed||Wants to help by making diagnosis easy; yields poor effort, might improve with suggestion|
|Suggestible innocent||Convinced that something is wrong after minor injury||Indifferent about inconsistencies of examination or behavior (“la belle indifference”)||Complacent; open to suggestions about improvement|
Classically, “la belle indifference” has been described as an important feature in all patients with hysterical vision loss (and used to distinguish it from malingering). This finding is likely present only in a minority of patients, however, and is most likely to occur in those characterized by the “suggestible innocent” profile. These patients with more subtle manifestations of functional visual loss might improve simply by reducing the amount of stress in their lives. Keltner found that 51 of 59 adults with functional vision loss were clearly seeking financial gain. They presumably fit best in the “deliberate malingerer” subgroup, but some patients may have been “worried impostors,” afraid they might miss some deserved benefit. Many adults with functional visual loss are consciously aware of the alteration of their examination. In children, triggering factors are often related to social issues, while adults have often suffered some traumatic event.
Types of Complaints
The diagnosis of functional visual loss will be made only if the examiner has a high degree of suspicion. Therefore, unless the patient comes with functional visual loss as the referring diagnosis or the patient is being seen for an insurance company or lawyer, the examiner must depend on the history, then the examination. With increasing experience, recognition of typical settings for organic and inorganic disease often suggests to the clinician that functional visual loss should be highly considered. For instance, head trauma is an important cause of traumatic optic neuropathy (see Chapter 5 ) and also is a common setting for functional visual loss. However, the characteristic severe blow to the brow or cheek that causes traumatic optic neuropathy is usually not described by a patient with functional visual loss. Similarly, a blow to the back of the head or a whiplash-type injury is unlikely to produce a traumatic optic neuropathy. In this setting, the examiner knows to be on guard and can tailor the examination from the beginning.
Patients with functional visual loss often have rather alarming chief complaints that identify the potential for secondary gain; for instance, “I am blind in my eye since the accident” or “I cannot see since I got that chemical in my eye.” However, as the examiner investigates further, the complaints become very vague, and patients are often unable to characterize the vision loss as anything more than absent or “blurry.” They will often answer, “I do not know” or “I cannot be sure” to questions directed at better characterizing the nature of the vision loss. They less commonly describe the symptoms characteristic of true optic neuropathy such a loss of brightness, darkening, pieces of vision missing, central blind spots, and altitudinal visual field loss. They are very unlikely to report metamorphopsia as patients with maculopathies might.
The major societal impact of functional visual loss is financial, in the form of undeserved benefits paid for fraudulent claims, missed work, and unnecessary testing. Most of the patients in Keltner’s series were unemployed. Convincing the examiner of a visual defect could result in a lifetime disability check as opposed to either dependency on public assistance or an ultimate need to secure employment. Keltner et al., noted that as many as one-third of claims from the Workers’ Compensation program may have been fraudulent. The problem is likely one that costs society millions of dollars per year. Ophthalmologists and optometrists can declare a patient legally blind; because of the financial impact they are obligated to be absolutely certain that functional visual loss is not present.
Functional Visual Loss in Children
The presentation of functional visual loss in children is often different from that in adults. First, the clinical suspicion for true or organic vision loss in children must be higher since the pediatric eye examination may be marked by poor cooperation or a lack of understanding of test procedures. Even when functional visual loss is “confidently” diagnosed, the patients must be followed closely for development of organic findings over time. Second, malingering, confrontational behavior, and pending insurance claims are infrequent in children. Lastly, children are less sophisticated and highly suggestible.
Functional visual loss has been estimated to occur in approximately 1 child per 1000 per year, and the most commonly encountered demographic group is pubescent girls (ages 9–11 years). There are often other accompanying symptoms such as headache, eye pain, and face pain. As with adults, functional visual loss may accompany organic visual loss.
Mantyjarvi found that only a few children had an underlying psychological illness causing the functional visual loss. In some children functional visual loss resulted from a lack of parental attention or conflict with parents. Divorce or relocation to a different school or city are common external stresses. Although not malingering, many children realize the secondary gain of increased parental attention as a result of their complaints of defective vision. In others, deterioration in school performance may trigger complaints of functional visual loss. In this setting there is often a mismatch between visual difficulty encountered at school and that noted at home. For instance, when the child is observed unknowingly, there may be no visual difficulty watching television or at play. Similar behavior may be seen in children who desire glasses because their friends have them.
A true conversion disorder may be present when the child is conscious neither of the loss of function nor of the potential secondary gain. Thus the functional visual loss allows the child to avoid a situation in which conflict occurs. Physicians should be alerted to the possibility of childhood physical or sexual abuse in this setting. In unusual circumstances, a parent drives the complaint of functional visual loss, thereby indirectly assuming the sick role ( Munchausen by proxy ).
Approach to the Patient With Functional Visual Loss
Every measure of visual function that requires the patient to respond or describe something is, by definition, subjective. In other words, patient cooperation and effort are required to obtain optimal results, especially with regard to testing of visual acuity, stereopsis, color vision, and visual fields.
The diagnosis of functional visual loss is suggested when the examiner can demonstrate that a patient’s behavior and responses to testing are inconsistent with an organic lesion. The diagnosis is confirmed when the examiner is able to prove, by some of the methods described later, that the patient has better vision than he or she claims. Although often tempting, the diagnosis of functional visual loss should not be made unless normal acuity and visual fields can be established and the pupillary and ophthalmoscopic examinations are also normal.
Alteration of the Patient–Physician Relationship
Often the examiner can immediately recognize that a patient’s behavior is inappropriate. This type of behavior frequently suggests the vision loss is functional and often sets the tone of the patient–physician interaction. The patient may be overly stoic or dramatic. Hostile, suspicious, flirtatious, or excessively cooperative behavior should make the examiner suspicious of functional visual loss. However, prejudices should not interfere with or alter the examiner’s empathetic attitude. The caring and genuinely concerned examiner will be the most successful at applying the tests that ultimately prove functional visual loss. Disbelieving or confrontational behavior is likely to make the patient uncooperative with testing.
Patterns of Functional Visual Loss
In most patients with nonorganic loss of vision, acuity and visual fields are both affected to some extent. However, several studies have suggested that the most common pattern is visual acuity loss with normal visual fields. Although it is somewhat artificial, the various techniques used to identify functional visual loss are described according to the level of visual dysfunction and whether the visual loss is monocular or binocular. It is essential that the examiner becomes familiar and comfortable with a few of the techniques that are used to identify functional visual loss. The testing should be performed in a routine and skillful manner without making the patient suspicious that the agenda is to prove functional visual loss.
It is important for the reader to note that while these techniques aim to prove that the vision is better than the patient claims, some of them are able to establish the actual level of vision in the supposed bad eye or eyes.
Observation . Throughout the course of the doctor–patient encounter the examiner must carefully observe the patient for behavior incompatible with the degree of alleged vision loss. Truly blind persons will always proceed cautiously around office furniture and equipment. They feel their way, and they will often bump into objects. Patients with functional visual loss, particularly deliberate malingerers, will move quickly and purposely bump objects but never fall or harm themselves. The examiner might intentionally line up the room with obstacles in the patient’s direct path to see how he or she navigates the room. Most truly blind patients will look in the direction of the examiner’s voice. The deliberate malingerer might not look at or may even avoid eye contact with the examiner, assuming that without vision, auditory clues would be inadequate to locate the other individuals in the room. Patients with functional vision loss may wear sunglasses for no apparent reason, and such individuals have a high rate of seeking secondary gain and often a diffusely positive review of systems. We have seen patients who took on the physical appearance, behavior, and head movements of famous blind people commonly seen in the media.
Pupillary reactions . Patients who are bilaterally blind (no light perception) because of retinal, optic nerve, chiasmal, or optic tract disturbances will have pupils that are unreactive to light. Only cortical blindness is associated with normal pupillary reactivity. Therefore, a complaint of total blindness with intact pupillary responses but no cortical lesion is likely to be functional. A complaint of photophobia with orbicularis contraction when the bright indirect ophthalmoscope light is shone in the eye is incompatible with an ocular cause of blindness.
Optokinetic nystagmus (OKN) . An optokinetic stimulus such as a drum or tape (see Chapter 2 ) produces a horizontal jerk nystagmus in patients with intact vision and an ocular motor system. The patient must look at and be able to see the figures or stripes on the drum or tape. The response is involuntary and implies a level of acuity equal to that necessary to resolve the stripes or other targets. Patients can voluntarily block this response if they look away from or beyond the stimulus. Excessive convergence on the part of the patient may also dampen the response. The use of a +3.00-diopter lens in front of the eye may force attention to the near stimulus and elicit a response. In the majority of cases, an intact OKN response confirms visual acuity to be at least 20/400. Although it is potentially possible to estimate a level of acuity by reducing the size of the object or stripe or using neutral density filters, this approach is not recommended.
Tests of proprioception . Truly blind patients have no difficulty performing tests that appear to require vision but are actually proprioceptive tasks. For instance, a patient can be asked to simply look at his or her hand. A blind person can do this easily, but a patient with functional visual loss will often look away from his or her hand. The patient also can be asked to bring the tips of the first finger from each hand together from a distance. This can be done without any vision and is easily performed by most blind patients. Patients with functional visual loss will often miss by inches. Finally, a blind person asked to sign his or her name will have no difficulty signing, while a functional patient will often produce a signature that is unlike his or her true signature and clearly is not along a horizontal line.
Mirror test . When a large mirror is placed in front of the face of a sighted person and rocked back and forth, an involuntary nystagmoid movement that results from forced fixation on the image in the mirror is produced. A patient with functional visual loss will be unable to avoid this movement provided he or she is looking at the image in the mirror. Acuity better than hand motions is present if this response occurs.
Surprise . Although generally too confrontational to recommend in most settings, actions that are designed to surprise and elicit a response from a patient can be quite effective. Various techniques have been described, and all generally involve some behavior atypical in a normal physician–patient interaction. The examiner can make faces or write shocking words and watch the patient for a response. A smile, gasp, or surprised look by the patient confirms that he or she can see and often ends with a “you got me, doc.”
Visual-evoked potentials and electroretinograms . Electrophysiologic testing has an important role in the evaluation of patients with functional visual loss. In a patient with purported complete blindness, the flash visual-evoked potential can be used to document intact visual pathways. In cooperative but functional patients, a pattern-reversal visual-evoked potential can provide an estimate of the individual’s true visual acuity. McBain et al. found that in 88 of 100 patients with functional vision loss, normal Snellen acuity could be demonstrated with a short-duration, pattern-onset visual-evoked potential. Multifocal visual-evoked responses have been used to demonstrate normal responses in patients with functional vision loss and abnormal computerized perimetry. However, in patients with suspected functional visual loss, an abnormal visual-evoked potential is difficult to interpret. The patient can voluntarily alter the amplitude and latency of the P100 peak by defocusing, not wearing corrective lenses, or looking away from the stimulus. Unfortunately, the opposite is also true, as normal responses have been documented in patients with organic visual loss.
Severe Unilateral Vision Loss
Techniques used on patients with severe bilateral vision loss can be applied to patients with severe unilateral vision loss by patching or covering the “good” eye. In fact, gross differences in behavioral observations and tests of proprioception when the examiner tests each eye separately are often the most compelling findings in this situation. The methods outlined here tend to emphasize the advantage the examiner has because of his or her understanding of binocularity and afferent visual pathway anatomy. It is important to observe the patient carefully while performing these tests since a “smart” patient may close the “good” eye periodically to try to figure out what the examiner is trying to do.
Afferent pupillary defect . Most patients with severe unilateral vision loss, with no history of amblyopia and with clear media, have a relative afferent pupillary defect (RAPD). Regardless of the localization of unilateral vision loss (optic nerve or chiasm), if the level of acuity is 20/200 or worse, an RAPD is usually present. Certainly nearly all patients with counting fingers or worse vision in one eye, with normal vision in the other, will have an RAPD. The examiner should exercise caution, because the RAPD is a subjective observation and may be absent in asymmetric cases of bilateral optic neuropathy despite very disparate levels of acuity. The absence of an RAPD should not be used to exclude an optic neuropathy, especially if there is a chance of preexisting or coexisting optic neuropathy in the other eye.
Stereopsis . In cooperative but unsuspecting patients, measurement of stereopsis can be invaluable in testing for functional visual loss because the results may prove the patient has better vision than he or she claims. Using an optical degradation technique, Levy and Glick determined the minimum level of acuity in each eye required to achieve each of the levels of stereoacuity on the Titmus test ( Fig. 11.2 ). Sitko et al. argued that the Levy and Glick study failed to account for individual variation. By studying their population of neuro-ophthalmic patients, Sitko et al. calculated that the ability to see nine of nine dots in stereo predicted at least 20/40 visual acuity in the worse eye with 95% certainty and at least 20/79 visual acuity with 99% certainty. Therefore a patient with a claim of reduced acuity to the 20/400 level in one eye but who sees 8 or 9 circles in stereo on the Titmus test almost certainly has functional visual loss. Unfortunately, some patients quickly close an eye and realize the test requires binocular vision and subjectively further alter their responses. As with the visual acuity testing strategy described later, it is often effective to begin the stereoacuity testing with the most difficult circles (the ninth) and act somewhat surprised if the patient denies appreciation of elevation of the circle. The great advantages of the stereoacuity testing are its widespread availability and the fact that a probable level of visual acuity can be demonstrated.