Functional Visual Loss (FVL) is a group of disorders presenting with visual symptoms such as decreased vision or visual field defects despite no organic abnormalities in the visual pathway. It is considered a subtype of Functional Neurological Disorder (FND). 1)
It is also called Non-Organic Visual Loss (NOVL), psychogenic visual loss, or conversion disorder. In DSM-5, it is classified as a somatic symptom disorder, and in ICD-11, as a bodily distress disorder.
It is broadly classified into three types.
In Japanese ophthalmic clinical practice, it is often divided into ophthalmic psychosomatic disorder and conversion visual disorder (hysteria).
| Non-conversion type (ophthalmic psychosomatic disorder) | Conversion type | |
|---|---|---|
| Age of onset | 6–15 years | 20s–30s and all ages |
| Affected eye | Often bilateral | May be unilateral |
| Subjective awareness of decreased vision | Poor | Clearly present |
| Psychological stress | Often not recognized | Often recognized |
In functional visual loss, patients unconsciously experience visual symptoms without intentional deception. Malingering involves intentionally feigning symptoms for external gain such as money or exemption, often accompanied by uncooperative attitudes during examinations or requests for medical certificates. Differentiation from malingering is detailed in the “Diagnosis and Examination Methods” section.
Conversion type patients often complain of vision loss themselves, whereas non-conversion type (ocular psychosomatic disorder) patients have few subjective symptoms and often visit the clinic after school vision screening detects low vision.
Conversion Type
Subjective symptoms: Patients complain strongly. They visit the hospital with chief complaints of decreased visual acuity and visual field defects.
Visual acuity: Tends to fluctuate with each examination. May improve with encouragement.
Typical complaints: Onset is relatively acute, and psychological triggers are often identified.
Non-conversion type (ocular psychosomatic disorder)
Subjective symptoms: Often scarce. Discovered during school health checkups or examinations for other diseases.
Visual acuity: Bilateral, often corrected visual acuity of 0.3 or less. Refraction fluctuates over several diopters.
Typical complaint: Common in 3rd-4th graders. May be associated with a desire for glasses.
Important clinical findings common to all types are shown below.
Normally, the visual field expands like a funnel as the examination distance increases, but in tunnel visual field, the size of the visual field remains almost unchanged even when the examination distance is changed. Along with spiral visual field and cloverleaf visual field, it is a characteristic finding in functional visual disorders.
The essence of functional visual disturbance can be understood as a message of “I have something I want to express” when the patient has an inner conflict that they cannot express even though they want to. However, the patient themselves are often unaware of what they want to express.
The desire for glasses is a good model of this condition. The conflict between “wanting to wear glasses” and “not being able to tell parents” remains unresolved and is converted into a physical symptom as a message of “not being able to see.” The patient themselves is unaware of this conversion process.
About 70% of triggers for functional visual impairment are related to home and school environments.
The diagnosis of FVL requires not only excluding organic diseases but also actively and positively diagnosing FVL.1)
MRI is recommended for all patients. It is essential to rule out stroke, multiple sclerosis, tumors, and posterior cortical atrophy.1) Basic tests include refraction with cycloplegic agents, visual acuity, intraocular pressure, pupillary light reflex, eye position and movement, binocular vision, slit-lamp examination, fundoscopy, and OCT.
The following organic diseases must be ruled out.
The main differentiating points between psychogenic visual disturbance and malingering are shown below.
| Item | Psychogenic visual disturbance | Malingering |
|---|---|---|
| Attitude toward examination | Cooperative | Uncooperative |
| External gain | None | Present |
| Request for medical certificate | Rare | Frequent |
| Consistency of symptoms | Fluctuates easily | Attempts to keep constant |
Multiple tests are combined for positive diagnosis. Visual acuity assessment using psychological tricks such as the trick method, fogging method, OKN drum, and mirror test is useful. Visual field findings such as tunnel vision and spiral visual field are characteristic, and dissociation between stereopsis and visual acuity also suggests FVL. VEP and electroretinography can objectively confirm normal retinal and visual cortex function. MRI to rule out organic central nervous system disease is also essential. 1)
The foundation of treatment is resolving and removing the psychological cause. Building a trusting relationship with the patient is most important, and the act of visiting the doctor itself becomes part of the treatment.
The basic principles of explanation are shown below.
In children, do not explicitly tell them it is psychogenic; guarantee recovery. Explain to parents at the time of diagnosis.
Treatment for Children
Prescription of placebo glasses: If the child desires glasses, prescribe glasses with no prescription. Be careful to avoid overcorrection.
Placebo eye drops (hugging eye drop method): Instill saline solution as a placebo. This method also serves as parent-child bonding and is effective for improving communication.
Observation: Continue observation until improvement is seen. It has been reported that symptoms disappear within one year in 85% of cases.
Treatment for Adults and Common Cases
Building trust: Repeated conversations with the patient to provide reassurance can lead to improvement.
Therapeutic use of diagnostic tests: Use OKN drum, fogging method, and mirror test to show the patient that “the brain can see.” The test itself functions as treatment. 1)
Collaboration with psychiatry and psychosomatic medicine: If depression, anxiety disorder, or PTSD are comorbid, consider referral to a specialist. Multidisciplinary collaboration based on the concept of psychogenic ophthalmology is important.
Wearing sunglasses provides temporary relief, but long-term use may increase light sensitivity. Gradual desensitization to light (stepwise reduction of sunglasses) is recommended. 1)
Informing the patient that there is no organic disease and that the condition is psychogenic can be effective. In adults, providing a diagnosis of “functional visual disorder” and explaining the prognosis may promote improvement. 1)
If no organic disease is evident, one should not write a medical certificate carelessly. Explain that subjective and objective findings are inconsistent, and that a period of observation is necessary to determine symptom fixation.
First, check if the child desires glasses; if so, prescribe placebo glasses with no prescription. Suggestion therapy using placebo eye drops is also effective. Instead of directly telling the child that the condition is psychogenic, provide reassurance that it will heal and continue follow-up. In children, symptoms resolve within one year in 85% of cases, but it is important to continue visits until improvement is achieved.
The most widely supported model currently is the predictive processing model. 1)
The brain constructs perception by “predicting” visual information based on past experiences. In FVL, the brain strongly predicts a state of “not seeing” and ignores updates to predictions from normal visual input. As a result, a state of “not seeing” occurs even though the eyes and visual pathways are functioning normally.
This mechanism is similar to phantom limb pain and is considered an expression of “abnormalities in brain networks related to agency, attention, and emotion” common to FND in general. 1)
A study of five patients with FVL using functional MRI reported the following findings. 1)
In the glasses-wish model, the desire to wear glasses and the conflict of not being able to tell parents remain unresolved, and are converted into a physical symptom as a message of “not seeing.” The patient is not aware of this conversion process.
The model of predisposing, precipitating, and perpetuating factors is organized as follows. 1)
It is explained by the predictive processing model. When processing visual information, the brain emphasizes “predictions” based on past experiences. In FVL, the prediction of “not seeing” becomes dominant, and the visual signals normally input from the eyes are not reflected in perception. It can be said that top-down predictions override bottom-up visual input. It is not intentional malingering. 1)
Transcranial magnetic stimulation (TMS) of the occipital lobe is attracting attention as a novel treatment for FVL.
Parain and Chastan (2014) reported that TMS was administered to 10 patients with FVL, and improvement was observed in 9 cases. 1) Occipital TMS induces phosphenes in the visual cortex, allowing patients to experience that visual cortical function remains.
There are over 30 studies on hypnotherapy for FND overall, including 5 RCTs. A consecutive case series of 8 patients with FVL reported improvement through suggestion tasks. 1)
In children, there are reports indicating the effectiveness of suggestion therapy. Abe and Suzuki (2000) reported that 28 out of 33 pediatric FVL patients recovered after receiving suggestion therapy. 1)
An approach that uses diagnostic tests as treatment is gaining attention. 1)
| Treatment | Evidence status | Target population |
|---|---|---|
| TMS | Case series (10 cases, 9 recovered) | Mainly adults |
| Hypnotherapy | Over 30 studies including RCTs (for FND in general) | Adults, children |
| Suggestion therapy (children) | 33-case series (28 recovered) | Children |
