Functional Visual Loss

Abstract

Functional visual loss (FVL) is a condition characterized by apparent blindness or visual impairment without any organic or structural abnormalities in the eye. This condition poses diagnostic challenges in both adults and children due to its varied presentations and potential overlap with genuine visual disorders. In adults, FVL is often associated with psychological stressors or underlying emotional conflicts, while in children, it may stem from factors such as family dynamics or school-related stress. Diagnosis of FVL requires a comprehensive evaluation of visual function using a range of clinical tests and ancillary investigations. Tailoring tests based on the laterality and severity of visual loss aids in diagnosis. It is imperative to rule out organic pathology and become skilled in techniques for identifying FVL without raising suspicion. Effective communication with patients and families is essential in management, emphasizing reassurance and avoiding unnecessary interventions. Prognosis for recovery is generally favorable, but recurrence risk underscores the need for ongoing support and follow-up care.

1. Introduction

Functional visual loss (FVL), also known as “non-organic visual loss” (NOVL), is when there is a decrease in vision without any physical eye problems. It is linked to disorders like conversion disorder, malingering, somatic symptom disorder, and factitious disorder [1]. FVL involves a decline in visual acuity and/or visual field without any organic lesion, even after a thorough examination by a neuro-ophthalmologist. This reduction in visual acuity can affect one or both eyes, ranging from mild blurriness to complete vision loss, with accompanying visual field defects like constricted or tunnel vision.

Functional visual loss (FVL) is a prevalent challenge encountered in both ophthalmic and neurologic practices, affecting 0.5–5% of patients with vision loss [1, 2]. Distinguishing between organic and functional visual loss holds crucial clinical and medicolegal significance. The intricate relationship between neuro-ophthalmology and non-organic dysfunction underscores the need for objective measurements to discern physiologic responses and confirm the integrity of the visual system.

According to Newman et al., functional visual loss is not merely a diagnosis of exclusion [2]; it necessitates positive findings to establish the diagnosis. It is essential to recognize that these findings may not always align with the patient’s primary complaint, and non-physiologic responses, while confirming, may not be sufficient for diagnosis. Coexistence of organic and non-organic disease further complicates the diagnostic landscape. In a retrospective analysis of two neuro-ophthalmologists’ cases [3], it was observed that 53% of patients displaying signs of functional visual loss concurrently presented with organic disease. Notably, in a study focusing on patients with idiopathic intracranial hypertension, 6% exhibited simultaneous functional visual loss, introducing complexities in decision-making regarding the appropriateness of surgical intervention [4].

In this chapter, we clarify terms, explore different patient types, and thoroughly examine methods for diagnosing functional vision loss. While various clinical issues can arise without an organic basis (e.g., nystagmus, gaze palsy, and ptosis), our discussion here specifically centers on cases involving visual acuity and visual field loss.

2. Terminology

Various non-organic (functional) disturbances are classified into three types [2, 5, 6, 7]: Malingering, Münchausen syndrome, and psychogenic disorders.

Malingering involves the conscious and voluntary production of symptoms. This behavior can manifest in various ways, including simulating a non-existent disease, exaggerating preexisting conditions, or attributing a disability to a different cause. Common settings for malingering include seeking compensation after a real or feigned injury, avoiding specific tasks like military service or exams, and attempting to garner special attention from family or friends.

Münchausen Syndrome is a distinct disorder that must be distinguished from malingering [8]. Unlike malingering, Münchausen Syndrome involves patients intentionally producing physical symptoms and signs, including ocular manifestations. Examples can range from swelling and redness of the conjunctiva, simulating orbital cellulitis to scarring of the eyelids and conjunctiva, and even chorioretinal scarring. These manifestations are then presented to medical professionals. Patients with Münchausen Syndrome are believed to have a psychological internal need to adopt the role of a sick person.

Psychogenic disturbance patients whose symptoms seem truly independent of volition are said to have a somatoform disorder or psychogenic disturbance. Examples of psychogenic disturbances include body dysmorphic disorder, conversion disorder (i.e., hysteria and conversion reaction), hypochondriasis, and somatization disorder [9]. Body dysmorphic disorder is characterized by a patient’s preoccupation with a perceived physical defect, often in the facial region. Conversion disorder diagnosis is established when physical functioning alterations express psychological conflict, with patients obtaining subconscious gains. Hypochondriasis involves the fear or belief in serious physical conditions accompanied by excessive self-observation. Somatization disorder features recurrent somatic complaints with vague descriptions and the presence of anxiety or depression.

In some cases, it is challenging to distinguish between malingering, Münchausen syndrome, and psychogenic or somatoform disturbances. In these instances, physicians should acknowledge the absence of an organic basis for the patient’s symptoms and signs and manage the patient accordingly.

3. Patient characteristics

Patients with functional visual loss exhibit diversity in socioeconomic backgrounds, lacking a clear sex or race predilection. Blue-collar workers [7] and Cambodians in California [10, 11], particularly those with a history of stress during incarceration, show a notable prevalence. In adults, there is a common association with preexisting psychiatric disorders [12].

“La belle indifference,” a traditional feature in hysterical vision loss distinguishing it from malingering, is typically observed in a minority of patients, with potential improvement noted in those who reduce stress in their lives [7]. Financial gain is a significant motivator, with many adults consciously aware of their altered examination [11]. Triggering factors in children often relate to social issues, while adults frequently associate functional visual loss with traumatic events [12]. Of note, 15–50% of the patients with FVL could have underlying visual comorbidities and fall under “non-organic overlay.” These cases need to be carefully evaluated and managed in order to avoid missing a subtle underlying treatable cause.

Diagnosing functional visual loss depends on a high level of suspicion, relying on patient history and examination, especially when there is no specific referral or when the patient is seen for insurance or legal purposes. Recognizing typical settings for organic and inorganic diseases helps consider functional visual loss. For instance, head trauma is an important cause of traumatic optic neuropathy 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 result in traumatic optic neuropathy. In these situations, the examiner knows to be on guard and customizes the examination right from the beginning.

Patients with functional visual loss often present 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, upon further investigation, the complaints become vague, characterized by absent or blurry vision, and lack the typical symptoms of true optic neuropathy.

Clues that need to raise suspicion of a functional disorder are described in Box 1.

When To Suspect FVL The story does not fit … (A minor trauma causing major visual loss) Inconsistent history and strange behavior… No/Inconsistent findings on the exam Chronic pain without good explanation History of anxiety and depression A functional disorder affecting other systems: the individual is in a wheelchair, but the reason is not apparent Multiple surgeries on various body parts, none of which revealed any pathology or provided significant relief

Box 1.

Tips when to suspect functional visual loss.

4. Approach to the patient with functional visual loss

The initial examination begins as the patient enters the clinic, where their ability to navigate around obstacles offers insight into their level of vision. Truly blind individuals exhibit cautious movements around office furniture and equipment, feeling their way to avoid collisions. In contrast, patients with functional visual loss, particularly deliberate malingerers, tend to move quickly, purposefully bumping into objects without risking harm. To assess this behavior, the examiner might intentionally set up obstacles in the patient’s path. Truly blind patients typically look in the direction of the examiner’s voice, whereas deliberate malingerers may avoid eye contact, assuming that auditory clues are insufficient without vision. Notably, a patient wearing sunglasses upon entering, without specific reasons like intense photophobia or an acute migraine attack, is reported as a strong indicator of non-organic visual loss [13].

It is important to establish if there is visual acuity loss or visual field loss and also if there is unilateral or bilateral loss. Reduced visual acuity is usually the most common presentation in FVL, and the approach depends on the laterality and severity. Severe bilateral or unilateral visual loss (no light perception) and moderate unilateral visual loss are generally easier to handle compared to mild or moderate bilateral visual loss. This difficulty arises because certain clinical tests and maneuvers rely on comparing responses between the two eyes, which becomes less effective when both eyes are compromised [2, 6, 7].

In cases of visual field loss, determine the area of visual field loss; this enables the examiner to tailor the tests necessary for a particular patient. Reduced visual acuity is usually the most common presentation in FVL. It is always important to rule out organic pathology. Various techniques for identifying functional visual loss are categorized based on the level of visual dysfunction and whether the loss is in one eye or both. It is crucial for the examiner to become familiar and skilled in few of these techniques, ensuring routine and skillful testing without raising suspicion about the underlying goal of proving functional visual loss.

4.1 Bilateral severe vision loss

4.1.1 Tests of proprioception

Truly blind individuals effortlessly perform tasks that may seem to require vision but are actually proprioceptive. For example, asking a blind person to look at their hand or bring the tips of their first fingers together can be done easily without vision. In contrast, patients with functional visual loss often look away from their hand or miss the target by inches, revealing difficulties in performing these tasks (Figure 1). Additionally, asking a blind person to sign their name poses no challenge, whereas a patient with functional visual loss may produce a signature unlike their true one, not following a horizontal line.

Figure 1.

A. A person who is truly blind can touch the tips of the fingers properly. B. A person with functional visual loss is often unable to touch the tips of the fingers properly (it can be tested with both eyes open in bilateral severe visual loss or with one eye covered in monocular severe visual loss as in B).

4.1.2 Visual surprise

Surprising actions, such as making faces or writing shocking words, can effectively elicit a response from a patient. A smile, gasp, or surprised look confirms their ability to see, often resulting in a playful acknowledgment. Menace reflex is a reflex blinking that occurs in response to a rapidly moving object. It is a protective response where the patient closes their eyes in anticipation of a threatening movement toward their face. While the menace reflex is a test described for detecting FVL, some practitioners avoid using it due to its perceived threatening nature. Additionally, the Riddoch phenomenon (refers to the ability of individuals with blindsight to perceive motion despite being cortically blind) [14] and the menace response alone cannot definitively diagnose or rule out FVL, potentially missing underlying treatable disorders [14, 15].

4.1.3 Pupillary reaction and absence of relative afferent pupillary defect (RAPD)

Patients with bilateral blindness (no light perception) due to retinal, optic nerve, chiasmal, or optic tract issues will exhibit unreactive pupils. Only cortical blindness is associated with normal pupillary reactivity. Thus, a claim of total blindness with intact pupillary responses but no cortical lesion is likely to be functional. Additionally, a complaint of photophobia with orbicularis contraction when exposed to bright light is inconsistent with an ocular cause of blindness.

In cases where a patient reports poor vision in one eye, it is expected to observe a relative afferent pupillary defect (RAPD) in that eye if there is an optic neuropathy or a retinal pathology such as central retinal artery occlusion. However, in patients experiencing unilateral profound vision loss to the extent of no light perception (NLP), the absence of RAPD despite a normal ophthalmic examination should raise suspicion for non-organic visual loss (NOVL). Assessing the absence of RAPD can be challenging in cases of bilateral or unilateral complaints with subtle or hemianopic loss. The use of neutral density filters may be necessary to verify the absence of RAPD, as subtle RAPD can be missed. Foroozan and Lee [11] highlight how an absent RAPD in a structurally normal eye could be mistakenly attributed to “faking” in the presence of a true underlying cortical visual field deficit that is detected through formal visual field testing. This is particularly relevant in cases of chiasmal or retrochiasmal lesions, where there may be no structural eye abnormality, normal 20/20 vision in both eyes, and no RAPD. It is worth noting that patients with early Leber’s hereditary optic neuropathy (LHON) may have a normal pupil response without RAPD, despite poor vision and a normal eye exam. The presence of a central scotoma and bilateral involvement are important clues that may prompt genetic testing in these individuals.

4.1.4 Optokinetic nystagmus

An optokinetic stimulus, such as a drum or tape, induces horizontal jerk nystagmus in individuals with intact vision and an intact ocular motor system (Figure 2A). The patient needs to observe the figures or stripes on the drum or tape for the response to occur, indicating a level of acuity sufficient to resolve the targets. This response is involuntary, and patients can intentionally block it by looking away from or beyond the stimulus. Hence, make sure the patient is not looking away and concentrating. Excessive convergence or the use of a + 3.00-diopter lens may dampen the response, but in most cases, an intact optokinetic nystagmus (OKN) response confirms visual acuity to be at least 20/400.

Figure 2.

A. The optokinetic nystagmus (OKN) test. To detect non-organic bilateral blindness. The patient is asked to look straight ahead with both eyes open while the drum is rotated. It can be used to detect unilateral blindness if one eye is covered. B. The mirror test. The patient is asked to look straight ahead into the mirror, and the mirror is then rotated and turned from side to side. Movement of the eyes indicates that the patient can see moving images in the mirror and, therefore, is not blind. It can be used for bilateral blindness or in case of monocular blindness, and then one eye is covered.

4.1.5 Mirror test

When a large mirror is rotated side to side in front of a sighted person’s face (Figure 2B), an involuntary nystagmoid movement is produced due to forced fixation on the mirror image. A patient with functional visual loss will exhibit this movement if they are looking at the image in the mirror, indicating acuity better than hand motions [2].

4.1.6 Ancillary testing

In cases where completely normal function is challenging to demonstrate but a non-organic cause is suspected, ancillary tests like visual evoked potentials may be occasionally useful. Normal visual evoked potentials with symmetric amplitude and latency in a patient with profound monocular visual loss support a functional etiology. Multifocal visual evoked potentials may show normal responses in the region of alleged visual loss [16, 17, 18, 19]. However, abnormal results are less conclusive. The patient has the ability to intentionally change the amplitude and latency of the P100 peak by defocusing, not using corrective lenses, or shifting gaze away from the stimulus [16, 17, 18]. Unfortunately, normal responses have also been observed in patients with organic visual loss.

Similar considerations apply to pattern and multifocal electroretinograms: a normal and symmetric response argues against the presence of severe organic disease, and an abnormal test is inconclusive. The flash electroretinogram measures the function of predominantly the outer retinal layers of cells involved in vision. It should be abnormal in a patient with diffuse retinal dysfunction but will be normal in a patient with more distal organic disease such as optic neuropathy, chiasmal neuropathy, or retrochiasmal visual dysfunction. Neuroimaging may help rule out obvious compressive or vascular lesions, but negative studies do not establish the diagnosis as functional. Indeed, Moster et al. [18, 19] found lesions on nuclear medicine imaging studies (single proton emission tomography (SPECT) and positron emission tomography (PET)) while evaluating two patients with suspected functional visual loss.

4.2 Monocular severe vision loss

Methods for patients with severe bilateral vision loss can be adapted for those with severe unilateral vision loss by covering the “good” eye. In this scenario, notable differences in behavior and proprioception during individual eye testing often provide crucial insights. 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. Observing the patient closely during these tests is essential, as a perceptive patient may periodically close the “good” eye to decipher the examiner’s intentions.

4.2.1 Stereopsis and visual acuity correlation

The correlation between stereopsis and visual acuity is based on the principle of binocular fusion, where stereopsis tests require a certain minimum level of vision to accurately measure the degree of stereopsis. This correlation is outlined in Table 1. Tests such as the Titmus test and Randot test (Stereo Optical Co., Inc., Chicago, IL) can be administered to patients without raising suspicion and can be used in cases of monocular or binocular loss to some extent [11]. However, it is important to note that some studies suggest that commonly used visual acuity estimates based on stereo acuity may overestimate actual visual acuity. Sitko et al. [20] conducted a study on neuro-ophthalmic patients and found that the ability to see all nine dots in stereo on a test predicted a visual acuity of at least 20/40 in the worse eye with 95% certainty and at least 20/79 visual acuity with 99% certainty. This means that if a patient claims to have reduced acuity to the level of 20/400 in one eye but can see 8 or 9 circles in stereo on the Titmus test, it is highly likely that they have functional visual loss. However, it is important to note that some patients may quickly close an eye and realize that the test requires binocular vision, leading them to subjectively alter their responses. To address this, it can be effective to start the stereoacuity testing with the most difficult circles (the ninth) and act surprised if the patient denies seeing the elevation of the circle [21].

Stereopsis (arc second)	Visual acuity	Visual acuity
40	20/20	6/6
43	20/25	6/7.5
52	20/30	6/9
61	20/40	6/12
78	20/50	6/15
94	20/70	6/24
124	20/100	6/30
160	20/200	20/60

Table 1.

The correlation between stereopsis and visual acuity.

Source: Data modified from (33).

4.2.2 Confusion tests with red-green glasses

4.2.2.1 Douchrome test

The duochrome test (Figure 3) is performed using the red-green glasses as the eye chart is projected through the red-green filter. The left half of the screen is green, and the right side is red. Without lenses or with red-green glasses and intact vision in both eyes, the red and green portions of the chart are seen. The test takes advantage of the fact that the eye looking through the red lens will see only the red (right) side of the chart. The eye looking through the green lens will see only the letters on the green (left) side of the chart. The red lens is typically placed over the right eye and the green over the left, but the orientation can be switched. To test for functional vision loss, the patient is asked, with the red-green glasses on and both eyes open, to read the whole eye chart. If the patient reads the whole chart, intact vision in both eyes has been proven. Note the completeness of the filters is dependent on the red-green compatibility of the lenses and the projector.

Figure 3.

The duochrome test is performed using red-green glasses, and the eye chart is projected through the red-green filter.

4.2.2.2 Color plates and the red-green lenses

Another test that utilizes red-green lenses and can be employed to determine at least 20/400 vision is the use of Ishihara color plates. These plates cannot be seen through a green lens. Therefore, if the red lens is placed over the eye that the patient claims has poor vision and the patient is able to read the plates, it indicates the presence of at least 20/400 vision in that eye.

4.2.3 Confusion test with polaroid glasses

A similar test involves using polarized glasses, with one axis at 90° and the other at 180° in each lens, and asking the patient to read a polarized eye chart with some letters perceptible only to one eye or the other. If the examiner moves quickly before the patient tries closing the good eye (which is not easily seen by the examiner because of the glasses), better acuity with the bad eye can usually be demonstrated.

4.2.4 Diplopia tests

4.2.4.1 Prism shift test

The prism shift test assesses binocular vision by selecting a Snellen letter smaller than the patient’s alleged acuity in the affected eye (If the patient claims 20/200 vision in the affected eye, perform the test with a 20/50 letter or smaller). Using a 4-diopter base-in loose prism, the patient views the target binocularly. If the patient truly sees with both eyes, a compensatory eye movement toward the apex of the prism is observed, followed by a convergence movement of the fellow eye. In cases of a genuinely defective eye, placing a prism over it does not elicit compensatory eye movements.

4.2.4.2 Prism dissociation

This test uses a vertical prism to separate images from the two eyes, aiming for the patient to unwittingly read letters corresponding to the line seen by the bad eye.

The examiner tricks the patient into thinking both images are seen by the good eye by briefly placing the prism over the good eye partially while intermittently causing monocular diplopia. Afterward, the prism is completely shifted over the good eye while uncovering the bad eye, resulting in true binocular diplopia. For example, if an 8-diopter base-up prism is held over the good eye, the patient is then asked to read the higher line. If the patient reads the upper line, the examiner has established the acuity of the bad eye at that level [21]. A simplified version, using a 4-diopter vertical prism as a screening tool, has been demonstrated by Golnik et al. to differentiate between patients with normal vision (seeing two images) and those with poor vision (seeing one image) with suspected non-organic vision loss, usually reporting seeing two images, except for those with occult organic pathology.

4.3 Moderate vision loss

The outlined methods for severe unilateral vision loss are beneficial for patients with moderate visual acuity loss (20/40 to 20/100). However, with more sophisticated patients in this range, proving better vision becomes challenging. In cases where better acuity cannot be shown, reliance on the presence of non-physiologic visual field loss is necessary to suggest non-organicity. Some of the following tests can be applied to binocular or monocular (with one eye covered) moderate visual loss.

4.3.1 Visual acuity tests

4.3.1.1 Distance doubling test

The correlation between testing distance and the patient’s visual acuity provides a means to verify functional visual loss. For instance, an individual with a visual acuity of 20/100 should be capable of reading the 20/50 line from 10 feet away (10/50 = 20/100). Manipulating testing distances often reveals non-organic responses. Patients with FVL often will report static, unchanged levels of vision despite coming closer to the chart [22, 23].

4.3.1.2 Bottom-up acuity

A reliable method to demonstrate better visual acuity is to initiate testing at the 20/10 line and gradually increase letter size, challenging the patient. It should be done in dark room, not to give clues to the real size of the optotypes. Encourage the patient positively for each successfully read letter or guess made during the test. Intermittent questioning and adjustments in letter size often lead to improved performance, with patients eventually reading lines they initially struggled with. This test can be done with both eyes open, particularly in cases of binocular visual loss.

In addition, employing “counting” acuity, where patients count letters even if unreadable, further reveals improved vision. Studies show that counting the 20/10 line corresponds to acuity of at least 20/30 or better, while counting the 20/25 line requires 20/80 acuity, and counting between 20/30 and 20/60 implies acuity of at least 20/200.

4.3.1.3 Near vision acuity

Evidence of functional visual loss can be observed through significant mismatches between distance and near acuities. Another simple test involves assessing near vision using a reading card with 20/20 size print. The patient reads smoothly with both eyes open, and then a pen is introduced between the eyes and the reading material. If the patient can still read smoothly without moving their head, it suggests both eyes can see, indicating functional visual loss.

4.3.1.4 Fogging test

The “fogging” test is used for patients with mono-ocular vision loss. It involves gradually blurring the good eye’s vision while the patient reads from a chart, encouraging them to use their “bad eye.” Light conversation can help distract the patient. In this test, a trial frame is used with plus and minus cylinders (4.00–6.00 diopters each) placed over the good eye. The correct distance refraction is applied to the bad eye, and if the patient’s refractive error is plano, a combination of plus and minus sphere lenses that sum to plano should be used. The patient reads the chart, and the examiner adjusts the trial frame while claiming to make adjustments. Rotating the lenses on both sides (the cylinder in the front of the trial frame and the sphere in the fellow eye) effectively blurs the good eye without the patient’s awareness and the patient continues to read with the bad eye. While a 20-degree rotation may be efficient, a 90-degree rotation achieves maximal blurriness (Figure 4).

Figure 4.

The fogging test. A. Prepare the trial frame. Place plus and minus lenses (4–6 diopters) in front of the “bad” eye and plus and minus cylinders (5–6 diopters) in front of the “good” eye (place one in the front frame and one in the back frame so one will rotate and the other will remain stationary). B. First, let the patient read from the chart with both eyes and lenses aligned. C. Rotate on both sides; in front of the “bad” eye with plus and minus diopters, the overall refraction will not change after rotation, but in front of the “good” eye with plus and minus cylinders now perpendicular to each other, vision will be fogged, and if the patient reads correctly, it indicates the “bad” eye has vision [22, 23].

4.3.1.5 The Mojon chart

The Mojon chart [24] is an optotype contour created by a subtle misalignment of two-line segments (vernier acuity). The minimum angle of resolution of such an optotype should be independent of its size if the lines are evenly spaced and the frequency of the lines remains constant (Figure 5A). This feature makes it particularly useful for detecting moderate visual loss. As a compact pocket card (Figure 5B), it offers versatility for testing either one or both eyes. The technique involves gradually bringing the chart closer to the patient until they can clearly see the largest figure displayed on it. Once the largest figure is visible, the examiner uncovers the rest of the chart and asks the patient what they can see. In a normal response, the patient should be able to recognize all the figures on the chart. If a patient claims to see only the largest figure and not the smaller ones, it can indicate non-organic visual loss. This method has been shown to have a high positive predictive value (PPV) of 100% and a negative predictive value (NPV) of 94%, indicating its reliability in identifying non-organic visual loss. It is crucial to conduct the test with the correct refractive correction, especially for reading purposes. Typically, the examination begins from a distance of approximately 2 meters, with only the largest figure visible.

Figure 5.

The Mojon chart. A. The new optotype contour is formed by a misalignment of two-line segments (Vernier acuity). Theoretically, the visibility of such an optotype should be independent of its size if the frequency of the lines remains constant. B. The pocket chart has eight different optotype sizes distributed on two sides.

5. Functional visual field loss

Visual field abnormalities can indicate non-organic causes in some cases. A common deficit seen in FVL is tunnel vision, restricting the usable field to the central 5–10 degrees. Normally, the visual field expands away from the target, similar to how we perceive objects like stars or the moon at infinite distances versus seeing a ball up close. This concept applies to patients with constricted fields, whether unilateral or bilateral. This test is typically conducted using a tangent screen. Initially, a monocular field is tested at 1 meter, with the screen marked based on the patient’s responses. Subsequently, the patient is moved to 2 meters, and the stimulus size is doubled. Upon retesting, many patients with functional visual loss exhibit tunneling without physiological visual field expansion. Simpler confrontation methods are also effective. The visual field is first assessed at 1 meter by moving a finger from the periphery into the patient’s seeing field to map out the approximate area. This process is then repeated at 2 meters or beyond. In normal or organically constricted fields, the mapped area should expand outward. Failure to expand indicates non-organic causes.

Accurate saccadic movements of an eye toward an alleged blind hemifield suggest non-organic visual field loss. The examiner informs the patient about testing eye movements. Initially, the patient follows the examiner’s finger with pursuit movements. Then, the patient is instructed to quickly look at the examiner’s finger presented in the blind hemifield; if the saccade is accurate, it implies an intact field. Patients often hesitate, claiming difficulty in peripheral vision. The examiner encourages them to focus with central vision, resulting in precise saccadic eye movements at times.

Goldman kinetic visual field testing, conducted by a skilled administrator, is often more reliable for assessment. In FVL cases, patients might exhibit constricted fields with non-physiological overlap of isopters. They may report seeing a smaller, dimmer object in the same location as a larger, brighter test object. This can result in a continuous spiral (Figure 6) or an irregular, jagged star pattern [2].

Figure 6.

A non-organic spiral field in a patient with non-organic (functional) visual field loss was tested with the Goldman kinetic visual perimeter.

Non-physiological narrowing of the visual field on computerized perimetry can manifest as a distinct pattern known as a “clover-leaf” defect (Figure 7). This typically involves rounded areas of spared vision surrounded by peripheral defects in all four quadrants, resulting in a clover-leaf appearance on the grayscale. Additionally, low-reliability parameters are often observed. Although “clover-leaf” is suggestive for FVL, it is not a diagnostic test [23]. Visual field narrowing that resolves with a suggestion or fluctuates over time suggests functional visual loss. When a patient exhibits field constriction in a Swedish interactive threshold algorithm (SITA) Standard 24-2 visual field test, we request a repeat test along with a 10-2 visual field assessment. If we observe a similar pattern of constriction in the 10-2 visual field, functional visual loss becomes more suspect, especially if no paracentral depression was noted in the 24-2 test. Compared to “clover-leaf” and non-physiologic visual field constriction, a central scotoma on field testing is unlikely to be caused by FVL and should prompt the clinician to investigate further for underlying optic nerve or retinal pathology.

Figure 7.

A clover-leaf defect in an eye with non-organic visual field loss was tested with the Humphrey visual perimeter using the Swedish interactive threshold algorithm (SITA) standard 30-2.

5.1 Non-organic “hemianopia”

Fabricated visual field defects like hemianopias and quadrantanopias can be simulated using automated perimetry. In these cases, reliability parameters such as false positives and negatives are not effective in detecting voluntary alterations of the field [24]. However, the presence of an inter-eye difference in mean threshold light sensitivity of 8.7 dB in patients with organic visual loss usually results in a Relative Afferent Pupillary Defect (RAPD). Therefore, if such a difference exists without an accompanying RAPD, functional visual field loss is likely [25].

Consideration should be given to the fact that when one eye is truly non-seeing, the good eye compensates for the missing field of the bad eye when visual fields are checked with both eyes open. In patients with FVL, monocular field loss persists even during binocular testing. This test remains useful even in patients reporting constricted or hemianopic visual field defects in one eye. If the reported defect persists during binocular testing, it suggests FVL (Figure 8), as the visual field should appear normal when the seeing eye is tested alone. Initially, establishing the functional status of the good eye with monocular field testing is advisable before binocular testing. Similarly, in patients claiming severe monocular visual loss, binocular visual field testing may reveal non-physiological constriction or absence of the visual field on the side of the monocular loss, a region visible during prior testing of the good eye alone.

Figure 8.

Non-organic unilateral hemianopsia. A. Each eye was tested individually; the left eye shows temporal hemianopsia, and the right eye is normal. B. When tested binocularly (i.e., both eyes are open during the test), there is still a complete temporal hemianopsia, indicating a non-organic visual field loss.

6. Functional visual loss in children

Functional visual loss in children is a significant concern, with up to 9% of school-aged children affected, translating to about 1.4 cases per 1000 children per year. This condition is predominantly observed in young girls aged 9–11, often referred to as “the amblyopic schoolgirl syndrome.” [26].

Despite the low incidence of psychological illness causing functional visual loss (FVL) in children [27], it should not be overlooked. Children with functional visual loss may also report on other physical symptoms such as headache or abdominal pain [28] as well as other mental health problems. The presence of such associated problems does not exclude a real pathological vision problem and the physician needs to examine carefully before reaching the conclusion of a functional visual loss.

Causes typically stem from the stress of puberty or pre-puberty, including underlying issues such as stress at home or school, abuse, or bullying, often leading to a cry for help. In some cases, it may result from a lack of parental attention or conflicts with parents, often triggered by events like divorce or relocation [29, 30].

However, malingering is rare, as they genuinely believe something is wrong and express anxiety about it. Among children with functional visual loss, distinct groups emerge, including the visually preoccupied child, who becomes overly concerned about their visual health, and those with conversion disorder, often linked to psychological stress or abuse [30].

While not malingering, some children realize they gain more attention from their parents when they complain of vision problems. Others may report functional visual loss due to deteriorating school performance [30], despite no observable difficulty with vision during activities like watching television or playing. Some children may mimic vision problems because their friends wear glasses.

Possible factitious disorders, such as Münchausen by proxy, may involve parents intentionally causing symptoms in the child, while cases with non-organic overlay highlight the challenge of distinguishing between genuine and exaggerated symptoms, particularly when symptoms persist or worsen.

Most of the children with functional visual loss fall into one of these four groups and it may help to remember these groups in the approach to diagnosing and managing them [27]:

1. The visually preoccupied child: these children become preoccupied with their vision and start to worry about their visual function. Some of them are convinced that the need glasses in order to function correctly. These children usually do not have serious personality disorders and many times simple reassurance helps in the gradual resolution of the symptoms.

2. Conversion disorder: Conversion disorder is a psychiatric term for a unconscious neurological function loss for a secondary gain. These children have an unconscious loss of vision. The child believes he or she cannot see. The gain is not to go to school, where the child has a problem or a conflict with a teacher or a classmate.

3. Some may develop a conversion reaction to sexual assault or abuse.

4. Possible factitious disorder: parents of these children display behavior of a factitious disorder by proxy (Münchausen syndrome by proxy); it should be suspected when one or both parents are overly invested in the child’s visual symptoms/loss and appear to actively encourage the symptoms. The child, unconsciously, cooperates with the parents. These parents often become hostile to the physician who suggests functional visual loss, interferes with the exam or explanations, refuses psychiatric evaluation, and does not return for a follow-up examination.

Functional visual loss superimposed on a true organic visual loss: many children with conversion disorder can have true organic disease. The psychogenic component can conceal or distract from a true problem. The child may exaggerate the symptoms in order to bring it to attention. Suspicion of such a condition should be raised whenever the visual symptoms are longstanding, progressing, and non-fluctuating. One should suspect an organic component also when the child reports symptoms while engaged in his or her favorite activities (sports, play, etc.).

When approaching children with unexplained visual loss, the ophthalmologist should take into account some underlying conditions that cause visual loss that is difficult to diagnose [27], such as amblyopia, refractive problems, corneal problems like keratoconus, occult retinal disease or causes of transient visual symptoms like migraine related transient visual loss, epilepsy, etc. Some conditions can manifest at early stages as a functional visual loss but eventually are diagnosed as true, organic visual loss, such conditions include early macular dystrophies, or Leber hereditary optic neuropathy. Children with a brain tumor, such as craniopharyngioma, may be diagnosed as functional visual loss because the tumor is already compressing the optic nerves, but there is still no visible pallor of the optic disc.

A very careful history taking and ocular examination, including cycloplegic refraction, should be conducted as well as using other tools such as optical coherence tomography (OCT), corneal topography, and visual perimetry, when possible, in children old enough to take the test. The use of OCT has increased the possibility of early diagnosis of occult retinal disease, as well as detection of early retinal nerve fiber layer (RNFL) loss of Ganglion cell layer (GCL) loss in optic nerve disease, including early changes from a compressive intracranial lesion affecting the optic chiasm and/or optic nerves.

Children with functional visual loss typically exhibit moderate binocular deficits in the range of 20/30–20/100 [27]. They often appear to exert great effort when attempting to read the eye chart, and their guesses are frequently inaccurate.

In contrast to adults, children are more easily encouraged or “tricked” to demonstrate normal visual acuity or visual fields with simple methods like using plano lenses or verbal encouragement. Many of the previously outlined tests for functional visual loss are also effective in children. For instance, “Bottom-up” acuity method, often combined with a low-power, negligible lens (0.125 D), can reveal better vision. Additionally, using “magic drops” such as topical anesthetics can be convincing. The examiner can explain that if vision improves with the drop, it will aid in understanding the eye’s problem. This test is particularly effective in children due to their suggestibility. Stereoacuity testing is another effective method since most young patients fail to realize it requires binocular vision.

7. Management of functional visual loss

7.1 Adults

Successful management of patients with non-organic neuro-ophthalmic symptoms starts with physician empathy and encouragement. Confrontation usually yields little benefit. Besides, refusing further tests or follow-ups and telling the patient there is nothing more to be done because nothing is wrong can exacerbate their frustration, potentially leading them to seek out another physician for repeated testing;

When making the diagnosis, it is important to explain it to the patient using clear language, such as “non-organic,” and assure them that it is not uncommon or abnormal. Describe it as a processing error in the brain or brain spasm rather than structural damage, emphasizing that their eyes can see but struggle to transmit information effectively. Also, emphasizing statements the patient is likely to agree with, such as good peripheral vision and healthy optic nerves.

Building on this understanding, instill confidence in the patient that their condition is potentially reversible and that they can work to correct the transmission error.

It is crucial to mention the absence of serious neurological conditions like brain tumors or strokes. Additionally, reassuring the patient that similar cases often see improvement over time can be helpful.

Various interventions have been reported to “improve” vision in patients with functional visual loss, including drops, low-power spectacles, contact lenses, and “retinal rest.” “Retinal rest” [31] was a military treatment for strained or tired retinas. Patients’ eyes were patched, isolated from auditory stimuli, and checked daily, often leading to spontaneous improvement. This approach is challenging to apply outside of a military setting.

Some researchers have explored techniques like transcranial magnetic stimulation and hypnotherapy to increase awareness about visual perception. Stone also mentions the successful use of propofol for brief sedation, particularly with non-organic motor deficits, as it instills a sense of being treated for a “disease” and promotes relaxation. However, the utility, benefits, and safety of these procedures remain uncertain due to insufficient evidence. Hypnosis and psychoanalysis can also be attempted. However, psychiatric intervention is rarely necessary or beneficial for most patients. Refer to Box 2 for a summary of how to manage patients suspected of FVL in the clinic.

How to manage a patient with FVL If you suspect FVL do not jump to conclusions Exam carefully Do not confront patient None judgmental “No anatomic explanation,” describe it as “brain spasm” “Luckily, we found no disease” Everything is working fine… “It will get better,…‘the vision will be clear” “by next week it will have recovered”

Box 2.

How to manage patients suspected of FVL in the clinic.

7.2 Children

When managing functional visual loss in children, effective communication with both parents and the child is paramount. During discussions with parents, it is essential to emphasize that no organic findings have been identified, reassuring them that the vision impairment is psychological in nature, akin to stress-induced headaches in adults. Parents should be encouraged to address any potential sources of stress at home or school and to de-emphasize discussions about the child’s visual difficulties to help mitigate symptomatology. Similarly, when speaking directly to the child, it is crucial never to dismiss their visual concerns but instead convey that they have a minor visual disturbance while ensuring that their eyes are healthy. Providing a gradual pathway for recovery over time and scheduling a follow-up appointment in 2 months can offer the child reassurance and a sense of support.

The rate of recovery varies between many studies but is usually high (37–100% within 1 year). This variation is perhaps due to the lack of standardization of the definition of “complete recovery.” Some physicians are satisfied that good vision is restored, and not all refer or consult with mental health professionals [28].

Referral to psychiatric treatment is typically reserved for children exhibiting specific indicators, such as a history of psychogenic disturbances, signs of mental disorders, significant impairment in daily functioning, a history of psychic trauma like sexual abuse, dysfunctional family dynamics, signs of factitious disorder by proxy, or chronic visual loss lasting longer than 3 months with no organic disease evident. While most children may not require psychiatric intervention for minor visual disturbances or non-organic overlay, those with more complex psychological factors or functional impairments may benefit from additional mental health support to address underlying issues and facilitate recovery.

7.3 Prognosis

While the prognosis for recovery is favorable, with an expected 80–90% chance of improvement, there remains a 10–15% risk of recurrence. Limited literature exists regarding the recovery of vision loss, and the outcomes reported are variable. Sletteberg et al. [32] reported that 51% of their group had good visual function, while Barris et al. [33] found that 78% of their participants showed improvement or normalization of vision.

Sisera et al., in their study focusing on children with Functional Visual Loss, documented subjective and/or objective improvement in 49% of cases at follow-up. Responses to the questionnaire revealed that while some patients experienced complete remission of visual symptoms, others reported remission within various timeframes, ranging from within 1 week to up to 1 year. Interestingly, no correlation was observed between the duration of visual symptoms and the age at onset or gender. Additionally, the consultation at the clinic was perceived as “supportive and helpful” by the majority of patients.

Many patients with functional visual loss do not persistently seek medical attention. While some may experience spontaneous resolution, others may remain “disabled” due to their vision loss. Patients with both organic and non-organic vision deficits pose significant diagnostic challenges, with no easy guidelines for management. However, discussing concerns about non-physiologic responses with the patient, especially for those identified as “worried impostors,” may be beneficial, as avoiding risky treatments could lead to improvement in the non-organic component of vision loss (Figure 9).

Figure 9.

Tests to diagnose functional visual loss.

Conflict of interest

The authors declare no conflict of interest.