REFERENCE · DIAGNOSIS

Functional Visual Symptoms

Refers to:

assessed functional visual loss or blindness;
blurred or reduced acuity, field or tunnel-type loss, and double-vision presentations; and
functional photophobia or difficulty accessing vision when supported by specialist assessment.

Scope boundary: Light sensitivity from migraine, eye disease or another cause is not automatically a functional visual symptom. The techniques below require ophthalmic or neuro-ophthalmic context and do not apply to generic dizziness or sensory overload.

Quick Reference

Presentation: Compare reported vision with objective visual behaviours or responses, such as optokinetic nystagmus, while also looking for eye and brain disease.

Visual acuity at different distances — compare acuity under selected viewing conditions.
Binocular versus monocular fields — compare field findings with one or both eyes viewing.
Optokinetic response — assess a visual response within specialist examination.

More techniques: See the full list below.

For the Person With FND
For Family, Friends, and Other Supporters
For Clinicians and the Care Team
Research and Sources —

For the Person With FND

Words may look blurred, part of the scene may seem missing, or sight may feel unavailable despite your eyes being open. Some people describe a narrow tunnel of vision. These experiences help explain what needs assessing; they do not identify the cause by themselves. Double vision and light sensitivity also need their own assessment rather than being assumed to be functional visual loss.

Functional visual symptoms may affect sharpness, the visual field or the sense that vision is available. The symptoms are real. Diagnosis depends on showing that some visual function is preserved in a way that does not match the reported difficulty, while also completing the examination needed to look for eye, optic-nerve and brain conditions.

One possible observation is optokinetic nystagmus: a striped target moving across the visual field can produce small tracking and resetting eye movements. That response may demonstrate that enough of the visual pathway is working to detect the moving pattern. It does not measure full visual acuity and cannot, by itself, diagnose functional visual symptoms. [1]

The clinician may choose other methods, such as fogging one eye or using a mirror, depending on the symptom. These are specialist examination tools, not tricks and not tests to repeat at home.

What the assessment can explain

A positive explanation should name the comparison that showed preserved vision and what it means for your particular symptom. A normal scan alone is not that explanation. Psychological distress is not required to establish the visual diagnosis. Ask which symptoms the finding explains and which still need investigation. [1]

Being understood in everyday life

Tell the team what happens when reading, recognizing faces, using a phone, travelling or working. A short chart test may leave unanswered how long you can use vision, what happens in busy surroundings and how much help you need. You can ask for information in an accessible format and for the explanation to be shared with your usual care team.

A useful assessment record separates the observed response from these daily needs. Ask about confidence, isolation, school or work participation and emotional strain without assuming they caused the symptoms. These are suggested discussion prompts, not a visual-disability score. Evidence about long-term outcomes is variable, and research often mixes visual signs with symptoms that actually trouble the person. [4]

Visual symptoms may be episodic or prolonged

Functional visual loss, blur, field change or visual access may come and go, fluctuate with the task or environment, or remain troublesome for long periods. Busy visual scenes, fatigue, migraine, light or sensory load may intensify symptoms for some people. A symptom being absent in a quiet examination room does not show that it was not disabling elsewhere.

When a familiar visual episode starts, stop driving, cooking, using tools, navigating stairs or another activity that depends on reliable vision. Sit or move to a safe position, use the visual aid and lighting strategy already recommended, and use only a previously trained visual or attention cue. Suddenly being unable to see from one or both eyes, or sudden severe eye pain, needs emergency assessment. New flashes, a dark shadow, painful eyes or changed vision need urgent advice. Do not drive yourself for emergency care; use the appropriate local service. [5]

For the Person With FND
For Family, Friends, and Other Supporters
For Clinicians and the Care Team
Research and Sources —

For Family, Friends, and Other Supporters

Do not wave objects toward the person’s eyes, set up obstacles or surprise them to see whether they avoid something. Those demonstrations can cause falls, distress or eye injury and are not a responsible diagnostic assessment. Support the person’s current visual-safety plan and report changes to the appropriate clinician.

Helping with the appointment

With permission, help prepare examples of the difficulty and questions about the findings. Ask whether lighting, large print, audio information, breaks or an accompanying person would make the visit easier. Let the person answer for themselves where possible. Ask for a written account of the positive evidence, any coexisting diagnosis and the follow-up plan.

When vision suddenly becomes less usable

An episode may settle quickly or last much longer. Help stop visually hazardous activity, provide the person’s usual mobility or visual support and reduce unnecessary visual complexity if that is part of their plan. Do not secretly test what they can see or remove sunglasses, lenses or another aid to make them practise.

Once safe, note what the person was doing, the type of visual change, whether one or both eyes seemed affected, duration, associated headache or neurological symptoms and recovery.

New, sudden or painful visual loss still needs urgent assessment according to local medical advice, even if the person has had functional visual symptoms before.

For the Person With FND
For Family, Friends, and Other Supporters
For Clinicians and the Care Team
Research and Sources —

For Clinicians and the Care Team

Featured technique: Positive demonstration of preserved visual function during a complete ophthalmic or neuro-ophthalmic assessment.
Diagnostic method: Compare reported vision with objective visual behaviours or responses, such as optokinetic nystagmus, while also looking for eye and brain disease.
Media needed: An orthoptist-, ophthalmologist- or neuro-ophthalmologist-led close-up demonstration.

Episodic and prolonged presentations

Clarify whether visual symptoms are continuous, intermittent or situational; document duration, frequency, visual environment, migraine or sensory context, associated neurological symptoms, functional risk and recovery. A normal interval examination does not itself establish a functional cause, and symptom fluctuation does not replace the positive visual examination and appropriate exclusion of ocular, optic-nerve and neurological disease.

For established episodic functional visual symptoms, give an onset plan that starts with driving/fall/injury safety and adapts a previously demonstrated preserved visual response, graded visual task or environmental strategy. Do not deliberately reproduce a visually provocative episode merely to confirm the history.

Choosing and documenting the assessment

Ophthalmology or neuro-ophthalmology leads the differential assessment; an orthoptist may contribute specialist binocular and visual-function testing. The whole care team needs the explanation and its limits. Record the symptom being tested, correction and viewing conditions, observed responses, alternative explanations, confidence and outstanding questions.

Coexisting eye and neurological conditions need their own assessment and care. The 2026 systematic review found ocular comorbidity across multiple studies, while an earlier specialist series documented abnormal neuro-ophthalmologic findings in 71 of 133 patients. These selected samples do not give a population prevalence. A functional finding does not make a new central field defect safe to dismiss. [3][4]

Choose acuity comparisons and fogging, field comparisons or the optokinetic observation to answer a defined clinical question. If the comparison is unreliable or does not address the reported symptom, document that limitation rather than forcing a positive diagnosis. Treatment planning belongs in the paired recovery section.

Technique outline: optokinetic response within a positive visual examination

The original seven-step outline is retained on the detailed optokinetic page.

Media contributor brief

The original recording brief is retained with optokinetic media and accessibility.

Diagnostic techniques at a glance

All thirteen entries are linked below. The full inventory preserves their descriptions and citations. Detailed guides cover selected comparisons; investigations are not positive FND tests.

Research and Sources

Evidence notes

The 2024 clinical article supports a positive, constructive explanation and assessment of coexisting disease. It is clinical guidance, not validation of a universal diagnostic battery. [1]
Optical and field comparisons should demonstrate preserved visual function and support a clear explanation. The 2022 review supplies technical descriptions; interpretation rests on the specific comparison and complete examination. [2]
The 2003 referral study supports vigilance for coexisting disease in a selected specialist population. [3]
The 2026 systematic review included 44 studies and 2,284 participants, with a search ending October 31, 2024. Most studies were retrospective. Prognosis data were heterogeneous, and signs were often not distinguished from symptomatic disability. This is not a diagnostic-accuracy meta-analysis and supplies no universal sensitivity or specificity for the methods here. [4]

Evidence reviewed October 10, 2026.

Citation table

Citation	Full citation
[1]	Ramsay N, McKee J, Al-Ani G, Stone J. How do I manage functional visual loss. Eye. 2024;38:2257–2266. FND-CIT-0024. https://doi.org/10.1038/s41433-024-03126-w
[2]	Raviskanthan S, Wendt S, Ugoh PM, et al. Functional vision disorders in adults: a paradigm and nomenclature shift for ophthalmology. Survey of ophthalmology. 2022;67(1):8-18. DOI: 10.1016/j.survophthal.2021.03.002. FND-CIT-0179.
[3]	Scott JA, Egan RA. Prevalence of organic neuro-ophthalmologic disease in patients with functional visual loss. American journal of ophthalmology. 2003;135(5):670-675. DOI. PMID: 12719075. FND-CIT-0180.
[4]	Ramsay N, Tessmann H, McKee J, Ercoli T, Stone J. Functional visual loss: a systematic review and meta-analysis of epidemiology, prognosis and treatment. Eye. 2026;40:1784–1793. DOI. FND-CIT-0103.
[5]	NHS. Vision loss. Reviewed August 28, 2025; accessed October 2, 2026. Safety guidance. FND-CIT-0104.

For the Person With FND
For Family, Friends, and Other Supporters
For Clinicians and the Care Team
Research and Sources —

Quick Reference

For the Person With FND

What the assessment can explain

Being understood in everyday life

Visual symptoms may be episodic or prolonged

For Family, Friends, and Other Supporters

Helping with the appointment

When vision suddenly becomes less usable

For Clinicians and the Care Team

Episodic and prolonged presentations

Choosing and documenting the assessment

Technique outline: optokinetic response within a positive visual examination

Media contributor brief

Diagnostic techniques at a glance

Visual acuity at different distances

Tubular visual fields

Spiralling, crossing or stacked isopters

Binocular versus monocular fields

Optokinetic response

Mirror tracking

Fogging

Prism dissociation

Prism fusion response

Stereopsis

Bagolini lens testing

Colour or polarizing dissociation

OCT, retinal testing and visual evoked potentials

Research and Sources

Evidence notes

Citation table