Functional vision disorders in adults: a paradigm and nomenclature shift for ophthalmology

      Highlights

      • Functional neurological symptom disorder (FND) is the current preferred nomenclature.
      • Patients with FND have symptoms incompatible with their signs or recognized medical conditions.
      • We propose “functional vision disorder” (FVD) to remain consistent in ophthalmology
      • There are many simple clinical examination techniques that aid the diagnosis of FVD.
      • The role of investigations is limited but often performed to exclude other pathologies.
      • Making and delivering the diagnosis promptly and without prolonged workup is important.
      • We propose adopting a standardized protocol (e.g., SPIKES) for consistent delivery of diagnosis.
      • SPIKES is used in other conditions to aid clinicians with communicating difficult diagnoses.

      Abstract

      Vision loss with clinical findings that are incompatible with the symptoms and recognized neurological or ophthalmic conditions is a common presentation of patients to neurologists, ophthalmologists, and neuro-ophthalmologists. The accepted terminology to describe such patients has evolved over time, including functional visual disorder (FVD), non-organic vision loss, non-physiologic vision loss, functional vision loss, psychogenic, psychosomatic, and medically unexplained visual loss. Likewise, attitudes and recommended management options have changed over the years in the fields of psychiatry and neurology. FVD is a diagnosis of inclusion, and it is critical that the diagnosis be made and delivered efficiently and effectively to reduce patient and physician duress. We review the current Diagnostic and Statistical Manual (DSM V) terminology and the prior literature on FVD and describe how the approaches to diagnosis and management have changed. We provide recommendations on the appropriate techniques and diagnostic approach for patients with FVD. We also propose a protocol for consistent and standardized discussion with the patient of the diagnosis of FVD. We believe that the adoption of FVD as both a paradigm and nomenclature shift in ophthalmology will improve patient care.

      Keywords

      1. Introduction

      Vision loss with clinical findings that are incompatible with the symptoms and recognized neurological or ophthalmic conditions is a relatively common presenting problem for ophthalmologists, neurologists, neuro-ophthalmologists, and psychiatrists [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Pula J.
      Functional vision loss.
      ]. In the modern psychiatric lexicon, these fit under the umbrella of functional neurological symptom disorder (FND, equivalent to conversion disorder), factitious disorder, and malingering. We propose functional vision symptom disorder (FVD) for cases where the symptom is visual in nature. In the past, there was a wide spectrum of terms used to describe FVD, including non-organic vision loss (NOVL), functional vision loss (FVL), non-physiologic vision loss, psychogenic vision loss, psychosomatic vision loss and medically unexplained visual loss (MUVL), which have fallen out of favor. In addition, outdated and pejorative terms for FND like hysteria have been removed from the revisions in the Diagnostic and Statistical Manual (DSM). We review the literature on FVD, including a discussion on how terminology and approaches to patient diagnosis and management have changed. We provide recommendations on the appropriate techniques and diagnostic approach for patients with FVD and propose a protocol for consistent and standardized discussion with the patient of the diagnosis of FVD (“SPIKES”). We believe that this paradigm and nomenclature shift will benefit both patients with FVD and their physicians.

      2. History of diagnostic terminology

      Improvements in our understanding of functional neurological symptoms disorders (FND) have prompted changes in disease terminology and diagnostic criteria over time. The Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association, has undergone 5 major iterations since its initial 1,952 version, each with substantial changes relating to both perceptions and understanding of medical terminology. There were only 128 diagnoses, and the first DSM1was only 132 pages in length. In contrast, the most recent version (DSM-5) has 541 diagnoses and 947 pages [
      • Blashfield R.K.
      • Keeley J.W.
      • Flanagan E.H.
      • Miles S.R.
      The cycle of classification: DSM-I through DSM-5.
      ]. In the original version (DSM-1) disorders were divided into organic brain syndromes and ‘functional’ disorders, which were further characterized into “psychotic, neurotic, and character disorders” [
      • Blashfield R.K.
      • Keeley J.W.
      • Flanagan E.H.
      • Miles S.R.
      The cycle of classification: DSM-I through DSM-5.
      ]. Functional disorders have been divided now into somatic symptom and related disorders, a heading that encompasses somatic symptom disorder, illness anxiety disorder, conversion disorder (i.e., FND), factitious disorder, as well as other specified and unspecified symptom and related disorders [
      American Psychiatric Association
      Diagnostic and Statistical Manual of Mental Disorders.
      ]. There have been substantial changes made between DSM-4 and DSM-5, including the overarching label of somatic symptom disorder to encompass multiple previously separated diseases, including somatization disorder, undifferentiated somatoform disorder, pain disorder, and hypochondriasis [
      American Psychiatric Association
      Diagnostic and Statistical Manual of Mental Disorders.
      ]. Similar changes have happened to the International Classification of Disorders (ICD) over time, although failure of ICD-10 codes to keep up with the DSM-5 classification does pose coding challenges when diagnoses are being made [
      • Gittinger J.W.
      Diagnosis and management of medically unexplained visual loss; one clinician's perspective.
      ].
      The changes in the DSM and ICD classification systems and nomenclature have also been reflected in the literature. We performed a search of the English language literature using Pubmed, Ovid Medline, EMBASE and the Cochrane Database of Systematic Reviews from dates of commencement until December 2,020. The following Medical Subject Headings (MeSH) were used in combination: “Vision, Ocular,” “Visual Fields,” “Visual Acuity,” “Visual Pathways,” “Evoked Potentials, Visual,” “Vision Disorders,” “Blindness” with “Malingering,” “Hysteria,” “Conversion disorder,” “Medically unexplained symptoms,” “Somatoform disorders,” “Psychophysiologic Disorders,” as well as the keywords “Functional vision disorder,” “Functional visual disorder,” “Functional vision loss,” “Non organic vision loss,” “Non physiologic vision loss,” “Factitious,” “Somatic symptom disorder,” “Medically unexplained vision loss,” “Functional vision loss,” “Perplexing presentations,” and “Perplexing symptoms.” A total of 1851 case reports, case series, trials, and review articles were identified, of which 666 were duplicates, and 752 were considered irrelevant as they did not include references to terminology associated with FVD. The titles of 433 case reports, case series, cohort studies and review articles were sorted into decade of publication to analyze changes in terminology over time, and the results are summarized in Fig. 1. It is evident that there has been a shift of nomenclature. “Hysteria,” which was more commonly used in the 20th century, has now been replaced in the literature with “functional” and “non-organic.” Hypochondriasis is now replaced by somatic symptom disorder and illness anxiety disorder. We recommend using the new nomenclature and avoiding the prior outdated terms “hypochondriasis” and “hysteria” that were removed from the DSM. The descriptor “conversion disorder” has overall remained stable. A more general review of preferred terms in functional neurological disorder broader than just vision suggests that the phrase “functional’ is patients” preferred descriptor [
      • Ding J.M.
      • Kanaan R.A.A.
      Conversion disorder: a systematic review of current terminology.
      ].
      Fig. 1
      Fig. 1Changes in descriptions of functional vision loss per decade in the literature.
      Many FND diagnoses previously listed in DSM-4 are under the broader heading “somatic symptom and related disorders” in the DSM-5. Others under this heading include somatic symptom disorder, illness anxiety disorder, and factitious disorder [
      American Psychiatric Association
      Diagnostic and Statistical Manual of Mental Disorders.
      ]. The current DSM-5 criteria for somatic symptom and related disorders are summarized in Table 1 [
      Somatic Symptom and Related Disorders
      Diagnostic and Statistical Manual of Mental Disorders.
      ].
      Table 1Summary of DSM-5 criteria for somatic symptom and related disorders, encompassing functional vision disorder (functional neurological symptom disorder with special sensory symptoms)
      Name of disorderFeatures of disorder
      • Levy N.S.
      • Glick E.B.
      Stereoscopic perception and snellen visual acuity.
      Somatic symptom disorder• One or more somatic symptoms that are distressing and disruptive to life
      • Excessive thoughts or feelings about the symptom manifest as either high anxiety, excessive time and energy, or disproportionate feelings and thoughts
      • Greater than 6 months in duration
      Conversion disorder (functional neurological symptom disorder) with special sensory symptoms (visual)• One or more symptoms of altered voluntary motor or sensory function
      • Clinical findings are incompatible with the symptoms and recognized neurological or medical conditions
      • No better medical or mental diagnosis to describe it
      • The symptom / deficit causes significant distress / impairment of function
      Further define as with / without psychologic stressor
      Illness anxiety disorder• Preoccupation with having / acquiring a serious illness
      • Somatic symptoms are either not present or mild
      • High anxiety about health and excessive health related behaviors
      • Duration greater than 6 months
      Psychologic factors affecting other medical conditions• A medical symptom / condition is present
      • Psychologic or behavioral factors adversely affect the medical condition (including exacerbation of symptoms, poor adherence to treatments)
      • There is no better mental disorder to describe it
      Factitious disorder• Falsification of symptoms or signs, or induction of injury or disease
      • Individual presents themselves as ill
      • Deceptive behavior is evident even in the absence of obvious external rewards
      • Can be imposed on self or another
      • No better mental disorder to describe it
      In part, these changes have been driven by patient response. Having patients who are engaged in their diagnoses with a strong provider-patient relationship is desirable in any field. Historically somatic disorders and FVD are areas fraught with challenges driven by provider discomfort and the patient being offended. Any perception the patient has of a provider thinking that they are “faking” their symptoms regardless of provider intention is likely to be met with resistance, particularly since symptoms and signs are not intentional in the vast majority of people with FVD. Multiple reports in the literature assess the “number needed to offend” (NNO) – a statistic measuring different responses by people based on the diagnosis given [
      • Ding J.M.
      • Kanaan R.A.A.
      What should we say to patients with unexplained neurological symptoms? How explanation affects offence.
      ]. In 1 study of general hospital outpatients, it was noted that the 2 most offensive diagnoses that could be offered to a patient were “psychogenic” and “somatic symptom disorder,” with an NNO of 3 [
      • Ding J.M.
      • Kanaan R.A.A.
      What should we say to patients with unexplained neurological symptoms? How explanation affects offence.
      ]. In comparison, the phrase “functional weakness” was considered much less offensive, with an overall offence score of 6% and NNO of 17, similar to stroke (offence score of 5.2% and NNO of 19) [
      • Ding J.M.
      • Kanaan R.A.A.
      What should we say to patients with unexplained neurological symptoms? How explanation affects offence.
      ].
      We define FVD to refer to a decrease in visual acuity and/or visual field that does not have an anatomic or physiologic basis [
      • Egan R.A.
      • LaFrance W.C.J.
      Functional vision disorder.
      ,
      • Vaphiades M.S.
      • Kline B.
      Functional neuro-ophthalmic conditions.
      ]. Consistent utilization of appropriate medical terminology for functional vision disorder will provide the patient with consistency in their diagnosis. We believe that the adoption of the term FVD in ophthalmology will reduce the NNO for patients as well as the anxiety and stress on the provider having to deliver the diagnosis.

      3. Diagnosis of functional vision loss disorder

      We recommend that the diagnosis of FVD follow the recommended diagnostic criteria as outlined in this manuscript, which is consistent with that in the DSM V for FND. Although the diagnosis of FVD requires “exclusion” of structural pathology to explain the symptoms, FVD should not be a “diagnosis of exclusion” alone [
      • Kathol R.G.
      • Cox T.A.
      • Corbett J.J.
      • et al.
      Functional visual loss: follow-up of 42 cases.
      ,
      • Krill A.E.
      • Newell F.W.
      The diagnosis of ocular conversion reaction involving visual function.
      ,
      • Lim S.A.
      • Siatkowski R.M.
      • Farris B.K.
      Functional visual loss in adults and children: patient characteristics, management, and outcomes.
      ].
      A thorough examination is necessary to avoid a false diagnosis of FVD, and a previous study report a misdiagnosis rate of 2%–3% [
      • Lim S.A.
      • Siatkowski R.M.
      • Farris B.K.
      Functional visual loss in adults and children: patient characteristics, management, and outcomes.
      ]. Patients from this case series were originally diagnosed with FVD and were later found to have non-functional diseases such as macular degeneration, unilateral optic neuropathy, NTG, cone dystrophy, Stargardt disease, and Leber hereditary optic neuropathy [
      • Lim S.A.
      • Siatkowski R.M.
      • Farris B.K.
      Functional visual loss in adults and children: patient characteristics, management, and outcomes.
      ]. Many patients who were misdiagnosed as FVD demonstrated inconsistent responses on testing suggesting functional disease, but in others the testing results were consistent with an underlying ophthalmic pathology [
      • Bose S.
      • Kupersmith M.J.
      Neuro-ophthalmologic presentations of functional visual disorders.
      ,
      • Kathol R.G.
      • Cox T.A.
      • Corbett J.J.
      • et al.
      Functional visual loss: follow-up of 42 cases.
      ,
      • Keltner J.L.
      • May W.N.
      • Johnson C.A.
      • Post R.B.
      The California syndrome. Functional visual complaints with potential economic impact.
      ,
      • Scott J.A.
      • Egan R.A.
      Prevalence of organic neuro-ophthalmologic disease in patients with functional visual loss.
      ]. Physicians should be aware that unreliable test results do not imply that a symptom is functional and many patients with visual field loss due to ophthalmic or neurological disease have superimposed variability and decline in automated perimetry reliability indices. Thus, “unreliable” alone is not sufficient to make a diagnosis of FVD in visual field assessment.
      Previous studies have documented coexistent FVD (i.e., functional overlay) with other ophthalmic or neurological disease in 26%–53% [
      • Bengtzen R.
      • Woodward M.
      • Lynn M.J.
      • Newman N.J.
      • Biousse V.
      The “sunglasses sign” predicts nonorganic visual loss in neuro-ophthalmologic practice.
      ]. Disorders such as strokes, central nervous system neoplasms, Alzheimer disease, multiple sclerosis, and side effects of psychiatric medications may present as vision loss concurrent with signs of psychiatric disease that can lead the physician to presume a diagnosis of FVD. Thus, neither does the presence of known neurological or ophthalmic disease pathology exclude FVD, nor does the presence of known psychiatric disease confirm FVD.
      Maintaining a high suspicion for and being rigorous about diagnosis of FVD is critical to avoid missed diagnosis and misdiagnosis. In the sections that follow we outline actions the provider can perform to collect data with which to support an FVD diagnosis.

      3.1 Observation

      Careful observation of the patient's behavior from the moment they enter the clinic can provide helpful information. People with vision impairment from ophthalmic or neurological disease typically walk cautiously and with a slight backwards tilt and may accidentally bump into objects [
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Incesu A.I.
      Tests for malingering in ophthalmology.
      ]. In contrast, some patients with FVD make exaggerated movements and bump into objects more than would be expected for their degree of visual loss if due to ophthalmic or neurological disease. Patients wearing sunglasses inside the physician office (the “sunglasses sign”) without an underlying reason for photosensitivity (e.g., migraine, corneal disease, optic neuropathy, etc.) can also be suggestive of FVD [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. Unlike patients with FVD, individuals who are blind from ophthalmic disease often wear sunglasses in public in order to cover a cosmetic deficit underlying or accompanying their blindness (e.g., corneal opacity, sensory strabismus, sensory nystagmus, or anophthalmic socket). Observation of tracking, hand shaking, filling out forms, and the interactions between the patient and the family/friends accompanying them with can provide further insights [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Lim S.A.
      • Siatkowski R.M.
      • Farris B.K.
      Functional visual loss in adults and children: patient characteristics, management, and outcomes.
      ].

      3.2 History

      The evaluation of any vision loss symptom begins by obtaining a detailed history from the patient. Information about the vision loss such as the onset, duration, triggering factors, alleviating factors, and associated symptoms should be elicited. Determining if the reported vision loss is monocular or binocular, as well as whether there is central vision loss (loss of acuity) or peripheral vision loss (loss of field) can help the physician localize a potential lesion and guides the rest of the history and physical exam [
      • Lim S.A.
      • Siatkowski R.M.
      • Farris B.K.
      Functional visual loss in adults and children: patient characteristics, management, and outcomes.
      ].
      The patient's past medical history, psychiatric history, ocular history, medications, and prior ophthalmic surgeries are relevant. Lim and coworkers reported a history of depression and/or anxiety in more than 30% of FVD patients [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. Other psychosocial factors such as social stressors at home or school, financial stressors, physical trauma, or sexual abuse may be associated with FVD; [
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ] however, subjective judgements about a patient's character should be avoided in all aspects of the patient assessment. The presence of these factors alone is neither necessary nor sufficient for making the diagnosis of FVL.

      3.3 Visual acuity

      A diagnosis of FVD is supported when evidence is collected to suggest a patient is able to see better than initially stated/demonstrated. This can be challenging; however, physicians can perform a variety of tests, without requiring specialized equipment, to demonstrate that the patient's vision is better than reported. Tests that show inconsistent responses not accounted for by known physiology raise suspicion for FVD [

      Beatty S. Non-organic visual loss. Postgrad Med J. 1999;75(882):201-207. doi:10.1136/pgmj.75.882.201

      ,
      • Kramer K.K.
      • La Piana F.G.
      • Appleton B.
      Ocular malingering and hysteria: diagnosis and management.
      ,
      • Miller B.W.
      A review of practical tests for ocular malingering and hysteria.
      ,
      • Smith C.H.
      • Beck R.W.
      • Mills R.P.
      Functional disease in neuro-ophthalmology.
      ,
      • Thompson H.S.
      Functional visual loss.
      ]. Table 2 summarizes the tests that can be used for patients reporting monocular or binocular vision loss.
      Table 2Clinical tests to evaluate the validity of vision loss
      TestTechnique
      Monocular vision lossFogging test“Good” eye blurred to elicit better vision than claimed in the “bad” eye
      Cylinder testUses paired cylinders to blur vision in both eyes. Vision in the “good” eye is corrected at a slower rate by the examiner to elicit better vision than claimed from the “bad” eye
      Stereoscopic testRequires good binocular vision. Stereopsis arc angle can be correlated to visual acuity
      Prism testDiplopia acknowledged by patient demonstrates good binocular vision
      Red-green color testingColored or polarized glasses worn by patient uncover true visual ability of each eye
      Pupil responseObjective test assessing the functioning of the afferent visual pathway
      Binocular vision lossObservationObserve inconsistent patient behaviors in movement throughout examination
      Bottom-up visual acuityBottom-up approach may elicit better visual acuity than top-down approach
      Size consistencyDecrease distance between patient and eye chart to determine if visual acuity improves as it normally should
      Finger-tip and signature testProprioceptive tests that do not require functional vision
      Mirror testElicits natural reflexes of miosis, accommodation, and convergence
      Optokinetic test using optokinetic drumInduces natural reflex of pursuit and saccadic eye movements

      3.3.1 Monocular vision loss

      In patients reporting monocular vision loss in whom FVD is suspected, the goal of the examination is to demonstrate that the patient can see better than reported in their symptomatic eye. Tests of binocular vision are often useful in this instance, [
      • Egan R.A.
      Functional visual loss.
      ] and best results are obtained when the examiner is professional, smooth, and appropriately describes the tests to the patient without divulging the binocular nature of the test.
      Fogging test: This works by blurring or “fogging” the vision in the patient's “good” eye [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. A plus spherical lens is placed in front of the “good” eye and a lens with minimal power over the “bad” eye. The visual acuity is tested with both eyes. Then, the strength of the plus lens is gradually increased without the patient's knowledge. Eventually, the fogging effect of the plus lens over the “good” eye will reduce the visual acuity and the visual acuity generated will represent vision in the “bad” eye. In our experience “fogging” may give away the intent of testing for FVD because patients can close each eye to determine the expected result.
      Cylinder test: In this test, a plus cylinder and minus cylinder lens of the same power are lined up in parallel over each eye [

      Beatty S. Non-organic visual loss. Postgrad Med J. 1999;75(882):201-207. doi:10.1136/pgmj.75.882.201

      ]. This alignment produces a lens with no refractive power [
      • Levy N.S.
      • Glick E.B.
      Stereoscopic perception and snellen visual acuity.
      ]. The examiner then rotates the lenses 90° causing blurry vision in both eyes. The patient is instructed to view a line on the vision chart that would normally be visible with the eye with good vision, but not the eye with bad vision. The examiner slowly rotates the lenses back to position, moving the lens in front of the eye with good vision more slowly. If the patient successfully reads the line, it can be attributed to vision from their eye with bad vision.
      Stereoscopic tests: Stereopsis, or binocular depth perception, is the ability to fuse the different images seen between the right and left eyes, and thus relies on binocular vision [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ]. Stereopsis can be tested by methods such as the Titmus stereo test in which the patient views a series of stereoptic symbols and images while wearing polarized glasses [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ,
      • Slavin M.L.
      The prism dissociation test in detecting unilateral functional visual loss.
      ]. The acuity of stereopsis in arc seconds can be suggestive of a minimum estimate of visual acuity [
      • Levy N.S.
      • Glick E.B.
      Stereoscopic perception and snellen visual acuity.
      ]. For example, the ability to see 40 arc seconds on the Titmus stereopsis test has been suggested to correlate to 20/20 visual acuity [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Newman N.
      • Biousse V.
      Diagnostic approach to vision loss.
      ]. FVD can be suspected when the patient's initially reported visual acuity is substantially worse than is suggested by the corresponding Titmus stereopsis test results. Normal stereoacuity, however, may not always reflect normal visual acuity, as noted in a more recent cross-sectional, observational study by Sitko and coworkers who found that, while there is correlation between poorer visual acuity and stereoacuity, the correlation suggested on the Titmus stereopsis test may overestimate the visual acuity, and substantial individual patient variation may exist [
      • Sitko K.R.
      • Peragallo J.H.
      • Bidot S.
      • Biousse V.
      • Newman N.J.
      • Bruce B.B.
      Pitfalls in the use of stereoacuity in the diagnosis of nonorganic visual loss.
      ]. Specifically, correct identification of 9 Titmus circles had a median worst eye VA of 20/22 with a 95% prediction interval boundary of 20/40 and 99% prediction boundary of 99% [
      • Sitko K.R.
      • Peragallo J.H.
      • Bidot S.
      • Biousse V.
      • Newman N.J.
      • Bruce B.B.
      Pitfalls in the use of stereoacuity in the diagnosis of nonorganic visual loss.
      ].
      Prism test: A prism (4 diopters is typically sufficient) is placed vertically in front of the patient's “good” eye and the patient is asked if they see 1 or 2 objects [
      • Mojon D.S.
      • Flueckiger P.
      A new optotype chart for detection of nonorganic visual loss.
      ]. A patient with monocular blindness will only be able to see 1 object with the prism in front of the good eye. Suspicion is raised for FVD if a patient reporting monocular blindness also reports the ability to see 2 objects out of the prism. Patients with reduced vision in 1 eye who see 2 lines can be asked if they are of similar clarity, or to read both lines. Ability to read both lines implies ability to see the tested optotype with both eyes.
      Another version of this test uses a 10-diopter base-out prism [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. The placement of this prism in front of 1 eye normally elicits movement of both eyes toward the apex of the prism, followed by a conjugate movement of the both eyes back to the center. In a patient with monocular vision loss due to ophthalmic disease, there will not be conjugate movement with placement of the prism over the affected eye.
      Colored/polarized lenses: The patient is given glasses with 1 red lens and 1 green lens and is instructed to read from an eye chart with alternating red and green letters [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ]. The red letters can only be seen with the red lens, and the green letters with the green lens. A variation on this is a split chart that has a black letter with a red background on one half and green background on the other. The polarized lens test works similarly by giving the patient polarized glasses with different axes in each lens and asking the patient to read from a polarized eye chart [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ]. The function of each eye is being individually tested in these tests.
      Optotype chart: The specialized chart consists of objects in decreasing size with an optotype minimum angle of resolution independent of the size of the objects [

      Beatty S. Non-organic visual loss. Postgrad Med J. 1999;75(882):201-207. doi:10.1136/pgmj.75.882.201

      ,
      • Bobak P.
      • Khanna P.
      • Goodwin J.
      • Brigell M.
      Pattern visual evoked potentials in cases of ambiguous acuity loss.
      ,
      • Grignolo F.M.
      • Moscone F.
      • Boles-Carenini A.
      Assessment of malingerers’ visual acuity by Lotmar's visometer test.
      ,
      • Keltner J.L.
      • May W.N.
      • Johnson C.A.
      • Post R.B.
      The California syndrome. Functional visual complaints with potential economic impact.
      ,
      • Sletteberg O.
      • Bertelsen T.
      • Hovding G.
      The prognosis of patients with hysterical visual impairment.
      ]. Patients with vision loss from an ophthalmic or neurologic cause could correctly identify all objects on the card, while patients with FVD may only see only the larger objects [
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Gittinger J.W.
      Diagnosis and management of medically unexplained visual loss; one clinician's perspective.
      ].
      Relative afferent pupillary defect: Testing for a relative afferent pupillary defect (rAPD) provides objective evidence about the functioning of the visual pathway from the retina to the optic chiasm. FVD might be suspected with the absence of rAPD in a patient with profoundly asymmetric vision loss [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Pula J.
      Functional vision loss.
      ]. The diagnosis of FVD should be strongly reconsidered in any patient with a rAPD.

      3.3.2 Binocular vision loss

      Binocular vision loss can be more challenging to evaluate and is a more common presentation of FVD than monocular vision loss, with previous studies reporting rates of 50–80% [
      • Zinkernagel S.M.
      • Mojon D.S.
      Distance doubling visual acuity test: a reliable test for nonorganic visual loss.
      ]. Many of the tests rely on demonstrating normal physiology of the brain and visual pathways to support a diagnosis of FVD.
      Snellen chart tests: One simple approach is to have the patient read the Snellen visual chart starting at the bottom line (ex. 20/10) and moving upwards [
      • Bose S.
      • Kupersmith M.J.
      Neuro-ophthalmologic presentations of functional visual disorders.
      ,
      • Zinkernagel S.M.
      • Mojon D.S.
      Distance doubling visual acuity test: a reliable test for nonorganic visual loss.
      ]. Oftentimes, good visual acuity can be documented by the time the patient reaches the 20/20 or 20/25 lines [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Weller M.
      • Wiedemann P.
      Hysterical symptoms in ophthalmology.
      ]. Physicians should provide repeated encouragement, give the patient sufficient time to read each line, and reassure the patient that the print will get bigger with each line.
      Similarly, changing the distance between the patient and the eye chart and recording the visual acuity at both distances has been shown to have high sensitivity and specificity in testing for FVD [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ,
      • Kramer K.K.
      • La Piana F.G.
      • Appleton B.
      Ocular malingering and hysteria: diagnosis and management.
      ,
      • Smith C.H.
      • Beck R.W.
      • Mills R.P.
      Functional disease in neuro-ophthalmology.
      ]. Decreasing the distance between the patient and the eye chart by 50% (e.g., 20 feet to 10 feet) will result in the line appearing twice as large, since the visual angle is doubled [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Weller M.
      • Wiedemann P.
      Hysterical symptoms in ophthalmology.
      ]. Thus, the patient should be able to read additional lines beyond what they could at the original distance. For example, a patient with a visual acuity of 20/100 at 20 feet should be able to read the 20/50 line at 10 feet. Patients with FVD may report the same visual acuity at both distances.
      Proprioception: Both the finger-tip test and signature test can be used [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. The patient is asked to perform simple proprioceptive tasks such as touching their index fingers together or signing their name on a piece of paper. These tests do not require a functional visual pathway, and a visually impaired patient due to ophthalmic disease could easily perform both tasks. FVD may be suspected if the patient exaggerates the inability to bring their index fingers together or produces a poor signature. In our experience, this is a useful test only in cases of severe visual loss.
      Mirror test: This takes advantage of the natural convergence, miosis, and accommodation reflexes that patients are usually unable to suppress [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. In this test, a mirror is suddenly produced and rotated in front of the patient. This naturally induces a pursuit movement, and the patient will track their image within the mirror. Like the proprioception test this test is only useful for patients with severe visual loss (e.g., worse than counting fingers to hand motions level).
      Optokinetic drum: An optokinetic drum, or any black and white striped object, is rotated slowly in front of the patient. The natural optokinetic reflex will result in smooth pursuit of the object followed by a quick saccade in the opposite direction as the patient refixates. If the fast and slow phase of nystagmus is observed, this suggests a visual acuity of at least 20/200 [

      Beatty S. Non-organic visual loss. Postgrad Med J. 1999;75(882):201-207. doi:10.1136/pgmj.75.882.201

      ,
      • Newman N.J.
      Neuro-ophthalmology and psychiatry.
      ].
      Other less quantitative tests use the concept of “shock” to demonstrate that the patient can see. The “menace test” involves the physician presenting a visual threat or cards or images with provocative images or words to the patient. The use of such threatening imagery (e.g., closed fist to the eye) and observing for an intact blinking or flinching reflex [
      • Bose S.
      • Kupersmith M.J.
      Neuro-ophthalmologic presentations of functional visual disorders.
      ,
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ] could easily be misinterpreted by outside observers, however, and likely are only of historic interest today. Other descriptions of physicians suddenly dropping an object to observe the patient's reflex reaction or even commenting on “money” (e.g., “Is that your $100 bill over there on the floor?” are entertaining, but also likely of historic value only. The sudden presentation of a bright light in front of the patient can also result in flinching or tearing [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. We do not recommend these types of “shock” tests for FVD as there are more objective and less objectionable tests available.

      3.4 FVD affecting visual field (VF)

      VF testing is a valuable portion of the ophthalmic exam because some results are highly suggestive of an underlying ophthalmic or neurological disease. A study by Scott and Egan found that all patients with a central scotoma had an underlying retinal or optic nerve disease [
      • Levy N.S.
      • Glick E.B.
      Stereoscopic perception and snellen visual acuity.
      ]. Bitemporal hemianopia and arcuate defects are also suspicious of underlying pathologies, and further workup should be considered in these cases [
      • Barris M.C.
      • Kaufman D.I.
      • Barberio D.
      Visual impairment in hysteria.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Incesu A.I.
      Tests for malingering in ophthalmology.
      ,
      • Keltner J.L.
      • May W.N.
      • Johnson C.A.
      • Post R.B.
      The California syndrome. Functional visual complaints with potential economic impact.
      ,
      • Thompson H.S.
      Functional visual loss.
      ,
      • Weller M.
      • Wiedemann P.
      Hysterical symptoms in ophthalmology.
      ]. Patients with FVD impacting VF most commonly report concentric loss of peripheral vision, resulting in tunnel vision [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ]. Automated and manual VF testing can provide the physician with helpful data when evaluating for FVD.
      Confrontation testing: Testing the VFs to confrontation at 1 and 2 meters can uncover non-physiologic results [
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ]. When the testing distance is doubled from 1 to 2 meters, the visual angle is also doubled. This principle results in a physiologic “funnel” vision rather than “tunnel” vision (Fig. 2) . Patients with FVD often do not demonstrate a wider field at further distance. This concept can also be tested using a tangent screen. The absence of VF expansion despite an increase in testing distance can raise suspicion for FVD.
      Fig. 2
      Fig. 2Normally, the visual field at 2 meters is doubled compared to the visual field at 1 meter. However, patients with functional vision loss may report the same size of visual field at increased distance.
      Saccade testing is another method to test the VF in patients with suspected FVD. This test can be framed as a test of eye movements rather than vision. The patient is asked to look at a small target that is initially held within their reported VF. Then, the examiner moves the target to random locations in the periphery outside of the patient's alleged VF. If the patient demonstrates accurate saccade movements to the target, this proves that their peripheral vision is intact [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ]. Other examination maneuvers that give VF information include finger to nose testing as is used for ataxia evaluation.
      Goldmann visual field: Classic findings on Goldmann VF testing suggesting a diagnosis of FVD include constricted VFs, crossing of isopters, and spiraling of the isopters (Fig.3); [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ] however, spiraling and crossing isopters can also both be the result of poor reproducibility and can be seen with fatigue [
      • Incesu A.I.
      Tests for malingering in ophthalmology.
      ]. Thus, the results from Goldmann VF testing can help provide evidence suggesting FVD, but no single test is diagnostic.
      Fig. 3
      Fig. 3Representative Goldmann visual field patterns suggestive of functional visual disorder. A. Symmetric constriction (tunnel vision) B. Spiraling of isopters C. Crossing of isopters.
      Crossing isopters may be elicited when a patient reports differences in the VF when using objects of different colors or sizes [
      • Weller M.
      • Wiedemann P.
      Hysterical symptoms in ophthalmology.
      ]. A spiral pattern may be generated if a patient's VF becomes more constricted with repeat testing at the same axis [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Keane J.R.
      Hysterical hemianopia. The “missing half” field defect.
      ]. If a patient returns for follow-up visits, the Goldmann VFs of each eye should be tested again, but in the opposite order. Reversing VF patterns between each eye are suggestive of FVD because there are no known ophthalmic or neurological disease processes that cause this result [
      • Scott J.A.
      • Egan R.A.
      Prevalence of organic neuro-ophthalmologic disease in patients with functional visual loss.
      ,
      • Smith T.J.
      • Baker R.S.
      Perimetric findings in functional disorders using automated techniques.
      ,
      • Thompson J.C.
      • Kosmorsky G.S.
      • Ellis B.D.
      Field of dreamers and dreamed-up fields: functional and fake perimetry.
      ].
      Binocular VF testing can be performed in patients with monocular VF defects to suggest the presence of FVD. With binocular testing, the “good” eye can compensate for the defect in the “bad” eye; however, patients with FVD may exhibit a persistent defect in the pattern of the monocular field defect on binocular testing (Fig. 4) [
      • Scott J.A.
      • Egan R.A.
      Prevalence of organic neuro-ophthalmologic disease in patients with functional visual loss.
      ]. Loss of the blind spot in binocular VFs in a patient with monocular blindness suggest FND [
      • Stewart J.F.G.
      Automated perimetry and malingerers. Can the Humphrey be outwitted?.
      ].
      Fig. 4
      Fig. 4Representative Goldmann visual fields with binocular testing for a patient with FVD claiming monocular vision loss. A. Left eye (OS) shows a temporal hemianopia B. Right eye (OD) shows a normal visual field C. Binocular (OU) visual field demonstrates a persistent temporal defect, indicative of a functional visual disorder. Physiologic results on binocular testing would demonstrate an enlargement of the visual field as the right eye compensates.
      Automated perimetry: Though some Goldmann manual perimetry findings suggestive of FND can be elicited on automated kinetic perimetry, the result of a constricted VF on automated monocular static perimetry cannot distinguish between a patient with ophthalmic disease and a patient with FVD [
      • Scott J.A.
      • Egan R.A.
      Prevalence of organic neuro-ophthalmologic disease in patients with functional visual loss.
      ]. Reliability indices such as fixation losses, false positives, and false negatives are similar in patients with underlying ophthalmic disorders and those with FVD. Furthermore, malingering patients have the ability to reproduce VF defects that are consistent with true ophthalmic and neurologic disease [
      • Scott J.A.
      • Egan R.A.
      Prevalence of organic neuro-ophthalmologic disease in patients with functional visual loss.
      ]. Previous studies reported that a cloverleaf pattern on automated VF testing is common in patients with FVD; however, these results should be followed with Goldmann VF testing for further confirmation [

      Creel D.J. Electroretinograms. Handbook Clin Neurol. 2019;160(1):481-493. doi:10.1016/B978-0-444-64032-1.00032-1

      ]. Unfortunately, the Goldmann perimeter and expert perimetrists are no longer universally available, and thus clinicians must gain comfort in using automated and non-automated (e.g., confrontation, saccade testing) VF testing methods to determine FVD.

      4. Work up

      Although the diagnosis of FVD can generally be made with suggestive history and clinical examination, further imaging and workup may be necessary to exclude other possible underlying ophthalmic or neurological disease especially in the setting of equivocal testing, or unreliable results. Optical coherence tomography (OCT) is useful for documenting the absence of structural retinal pathology in such cases. [
      • Bruce B.B.
      • Newman N.J.
      Functional visual loss.
      ,
      • Kramer K.K.
      • La Piana F.G.
      • Appleton B.
      Ocular malingering and hysteria: diagnosis and management.
      ]. In addition, neuroimaging (e.g., computerized tomography [CT] or magnetic resonance imaging of the brain [MRI] and orbits) to evaluate for structural pathologies may be necessary, but would be expected to be normal as there is no structural correlate to FVD on conventional neuroimaging studies [
      • Aybek S.
      • Vuilleumier P.
      Imaging studies of functional neurologic disorders.
      ]. Research is ongoing into abnormalities in functional MRI in other functional neurological disorders, but have not yet been utilized for FVD [

      Xu S., Meyer D., Yoser S., Mathews D., Elfervig J.L. Pattern visual evoked potential in the diagnosis of functional visual loss.; 2001.

      ]. The visual evoked potential (VEP) assesses the cortical electrical response to visual stimuli, and may be normal in FVD, although it may also be abnormal in patients who defocus or do not fixate on the target [
      • Levy N.S.
      • Glick E.B.
      Stereoscopic perception and snellen visual acuity.
      ]. Electroretinogram (ERG) can be used to suggest retinal pathology [
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Dhanji S.
      • Lawlor M.
      • Shindler K.
      • Galetta S.
      • Volpe N.
      Functional visual loss.
      ,
      • Gittinger J.W.
      Diagnosis and management of medically unexplained visual loss; one clinician's perspective.
      ]. We generally do not recommend VEP and ERG for patients in whom normal function of the visual pathway has been proven to the providers satisfaction using examination techniques; however, some patients and clinicians are reassured by normal electrophysiologic testing in cases where underlying (or concurrent) ophthalmic or neurological disease may be present.

      5. Treatment of FVD

      Common themes throughout the literature exist on the management of FVD. It is generally accepted that early and clear diagnosis, as well as avoiding prolonged or multiple workups, is important [
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Dhanji S.
      • Lawlor M.
      • Shindler K.
      • Galetta S.
      • Volpe N.
      Functional visual loss.
      ,
      • Pasol J.
      Nonorganic visual disorders.
      ,
      • Vaphiades M.S.
      • Kline B.
      Functional neuro-ophthalmic conditions.
      ]. Stressing lack of structural damage to the visual pathway is important, with at least 1 follow-up visit for reinforcement and to maintain a trusting therapeutic relationship with the patient [
      • Chen C.S.
      • Lee A.W.
      • Karagiannis A.
      • Crompton J.L.
      • Selva D.
      Practical clinical approaches to functional visual loss.
      ,
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Vaphiades M.S.
      • Kline B.
      Functional neuro-ophthalmic conditions.
      ]. Confirming that the symptoms are real, not their fault, and due to FVD, not ophthalmic or neurological disease, is also important [
      • Aoun S.M.
      • Breen L.J.
      • Oliver D.
      • et al.
      Family carers’ experiences of receiving the news of a diagnosis of Motor Neurone Disease: a national survey.
      ,
      • Baile W.F.
      • Buckman R.
      • Lenzi R.
      • Glober G.
      • Beale E.A.
      • Kudelka A.P.
      SPIKES—a six-step protocol for delivering bad news: application to the patient with cancer.
      ,
      • de Medeiros Nunes Pinheiro Peixoto V.G.
      • Diniz R.V.Z.
      • de Oliveira Godeiro C.
      SPIKES-d: A proposal to adapt the SPIKES protocol to deliver the diagnosis of dementia.
      ,
      • Novak I.
      • Morgan C.
      • McNamara L.
      • te Velde A.
      Best practice guidelines for communicating to parents the diagnosis of disability.
      ]. There are excellent on-line resources that can educate the physician so they can appropriately field questions, including at one of the authors’ institution (https://med.stanford.edu/psychiatry/patient_care/fnd.html). In some ways, delivering a diagnosis of FVD can be seen as analogous to “breaking bad news” – the clinician often feels uncomfortable doing it, there is a risk that the patient misunderstands the information, it challenges the therapeutic relationship, and management options are not as straightforward as prescribing a medication. The “SPIKES” protocol, first developed by oncologists to provide a structured approach to delivering bad news in patients with cancer diagnoses, has subsequently been modified and applied to delivery of other diagnoses as well, including motor neuron disease, disability diagnoses, and dementia [
      • Hilkert S.M.
      • Cebulla C.M.
      • Jain S.G.
      • Pfeil S.A.
      • Benes S.C.
      • Robbins S.L.
      Breaking bad news: a communication competency for ophthalmology training programs.
      ]. The 6 steps, which we have modified to an FVD approach, are illustrated in Table 3. Efficacy of this approach in other settings has been documented in the literature, with clinicians and students reporting that having a structured approach allows for more effective communication of the diagnosis. A pilot study ousing the SPIKES protocol and standardized patients in ophthalmology residency teaching was deemed beneficial by all involved [
      • Dattilo M.
      • Biousse V.
      • Bruce B.B.
      • Newman N.J.
      Functional and simulated visual loss.
      ,
      • Dhanji S.
      • Lawlor M.
      • Shindler K.
      • Galetta S.
      • Volpe N.
      Functional visual loss.
      ,
      • Egan R.A.
      • LaFrance W.C.J.
      Functional vision disorder.
      ,
      • Gittinger J.W.
      Diagnosis and management of medically unexplained visual loss; one clinician's perspective.
      ,
      • Pasol J.
      Nonorganic visual disorders.
      ,
      • Pula J.
      Functional vision loss.
      ,
      • Vaphiades M.S.
      • Kline B.
      Functional neuro-ophthalmic conditions.
      ].
      Table 3The SPIKES protocol, which we have modified for discussion of the FVD* diagnosis with the patient
      S: SETTING up the interviewClinician preparation
      • Clinician should be mentally prepared for the discussion, including as required mentally rehearsing the planned direction of discussion, possible questions and answers from the patient.
      Clinical setting
      • Ideally private room
      • Everyone should be sitting down to
      avoid feeling rushed
      • Manage time constraints and interruptions
      Patient and family should be prepared for the discussion
      P: PERCEPTIONAssess the patient's perception of their vision capacity
      Assess insight, as well as expectations
      Identify what the patient already knows or suspects about their illness
      I: INVITATIONBe aware that not all patients want to know all aspects of their condition – assess each situation individually to determine who much and which information is provided.
      If patients report not wanting to know about their condition, offer to discuss details in the future or with a friend/family member.
      K: KNOWLEDGEGive knowledge at the level of comprehension of the patient
      Emphasize that the symptoms are real and do not have any anatomic or physiologic basis
      Focus on good visual prognosis
      Avoid excessive bluntness
      Provide knowledge in small easy to understand ‘chunks’
      E: EMOTIONSRespond to patient's emotions with empathic responses
      • Observe the emotion
      • Self-identify the emotion
      • Identify the reason for the emotion
      After giving the patient time to connect with their emotion, make a comment that connects with the emotion.
      S: STRATEGY and SUMMARYClarify if the patient wishes to discuss management at this time, or in the future
      Provide a clear plan for the future, including emphasizing good visual prognosis
      Depending on patient factors and individual situation, consider whether further psychology/psychiatry input would be beneficial.
      FVD = functional vision disorder.
      First line treatment is education of patients and families. There are many excellent on-line resources geared towards patients. The ophthalmologist must be sure that any concurrent ophthalmic disease is appropriately treated and that the patient has necessary eye health monitoring. Ensuring appropriate providers are in place form managing of concurrent neurological disease is also important. Opinions differ as to the role and timing of referral to psychiatry or psychology. In our experience informing the patient that psychiatrists and psychologists are experts in treatment approaches that might be helpful is appreciated. In larger academic centers FND subspecialists are becoming more common. While there have not been any trials for treatment of FVD, cognitive behavioral therapy may be efficacious in other functional neurological symptoms, and this as well as referral to a psychologist or psychiatrist could be considered depending on the individual patient's situation [
      • Espay A.J.
      • Aybek S.
      • Carson A.
      • et al.
      Current concepts in diagnosis and treatment of functional neurological disorders.
      ]. In our experience regular eye care visits can be helpful both to the patient who may develop new vision symptoms and need help differentiating if from FND or something else and to other providers who often lack the expertise to differentiate FND visual symptoms from those due to ophthalmic disease. Prognosis of FVD varies and is often better with rapid workup, early diagnosis, and in younger patients [
      • Espay A.J.
      • Aybek S.
      • Carson A.
      • et al.
      Current concepts in diagnosis and treatment of functional neurological disorders.
      ]; however, the overall prognosis is thought to be poor, with disability persisting or even worsening over time [
      Somatic Symptom and Related Disorders
      Diagnostic and Statistical Manual of Mental Disorders.
      ].

      6. Conclusion

      FVD is relatively common in the ophthalmology clinic and may be associated with other functional neurological symptoms, as well as psychiatric, medical and ophthalmic comorbidities. The diagnosis requires a complete ophthalmologic examination confirming lack of ophthalmic or neurological disease to account for all symptoms, as well as to elicit signs of functional disease. Prolonged workup and investigation, as well as poor delivery of the diagnosis, should be avoided, and use of a standardized protocol (e.g. SPIKES) may be beneficial in discussing with the patient the diagnosis. Areas of future study could involve evaluation clinically of a standardized protocol like the one we described, or efficacy of treatments including cognitive behavioral therapy or pharmacotherapy. Although ophthalmologists and neurologists do not have to know its entire contents, we believe that the paradigm and nomenclature advocated in the DSM V should be adopted by clinicians caring for patients with FVD and FND.

      Authors’ contributions

      Subahari Raviskanthan: Conceptualization, methodology, validation, resources, data curation, writing – original draft, writing – review and editing, visualization, supervision. Sydney Wendt: Conceptualization, methodology, validation, resources, data curation, writing – original draft, writing – review and editing, visualization, supervision. Peter M Ugoh: Conceptualization, methodology, validation, resources, data curation, writing – original draft, writing – review and editing, visualization, supervision. Peter W Mortensen: Conceptualization, methodology, validation, resources, data curation, writing – original draft, writing – review and editing, visualization, supervision. Heather E Moss: Conceptualization, methodology, validation, resources, data curation, writing – original draft, writing – review and editing, visualization, supervision. Andrew G Lee: Conceptualization, methodology, validation, resources, data curation, writing – original draft, writing – review and editing, visualization, supervision.

      Guidelines for literature searching

      A search of English language published literature was performed using Pubmed, Ovid Medline, EMBASE and the Cochrane Database of Systematic Reviews from dates of commencement until December 2020. The following Medical Subject Headings (MeSH) were used in combination: “Vision, Ocular,” “Visual Fields,” “Visual Acuity,” “Visual Pathways,” “Evoked Potentials, Visual,” “Vision Disorders,” “Blindness” with “Malingering,” “Hysteria,” “Conversion disorder,” “Medically unexplained symptoms,” “Somatoform disorders,” “Psychophysiologic Disorders,” as well as the keywords “Functional vision disorder,” “Functional visual disorder,” “Functional vision loss,” “Non organic vision loss,” “Non physiologic vision loss,” “Factitious,” “Somatic symptom disorder,” “Medically unexplained vision loss,” “Functional vision loss,” “perplexing presentations,” perplexing symptoms.”

      Conflict of interest

      The authors report no commercial or proprietary interest in any product or concept discussed in this article.

      Funding

      This manuscript was supported in part (HEM) by an Unrestricted Grant from Research to Prevent Blindness to the Stanford Department of Ophthalmology and NIH (P30 026877). The other authors report no funding.

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