Functional visual loss

Functional visual loss (FVL) also known as Functional vision loss or Nonorganic visual loss (NOVL) is a reduction in visual acuity or loss of visual field that has no physiological or organic basis. This disease can come under the spectrum of functional neurological disorder or somatic symptom disorder.

Disease

In ophthalmology, Functional visual loss is the reduction in visual acuity or visual field that has no physiological or organic basis. This disease can come under the spectrum of functional neurological disorder or somatic symptom disorder under the categorization of the Diagnostic and Statistical Manual of Mental Disorders-5. But recent updates in the DSM-5 state that many patients with FVL do not have any identifiable psychological correlates.

Epidemiology

The prevalence of Functional visual loss neuro-ophthalmology clinics is said to be 5-12%, and general ophthalmology clinics 1-5%. It is said that the total prevalence may be much more higher because patients may also consult their general practitioners, internal medicine physicians, psychiatrists or neurologists.

It is more commonly seen in children at the age group 11–20 years and is seen more commonly in females (63%) than males. Children usually complain bilateral blindness.

Impact

The social impact of functional vision loss is largely economic. Unrecognized functional vision loss leads to fraudulent claims and undeserved benefits to the people. In case of legal blindness; Because of the financial impact and legal benefits including financial aids or reservations, optometrists and ophthalmologists are obligated to be absolutely certain that functional vision loss does not exist.

History taking

History taking very important in assessing Functional visual loss. It is very important not to allow any friend or relative into the examination room as the presence of another can influence the patient's behavior and thereby the diagnosis. It is also important that the patient never feels that the examiner suspect the patient is malingering, as this will make the patient more alert. So as usual do the exam calmly and quickly as routine work.

All complaints, including conflicting ones, as well as all symptoms reported by the patient should be recorded in their own words. Time of entry into the room, state of mind upon entering the room, type of seating, psychological profile and reactions should be recorded. Those records may sometimes be required in future judicial investigations.

Diagnosis

Visual loss must first be presumed to be functional, with no other causes. Almost all ophthalmic sensory and motor functions should be checked, including a visual acuity test, a visual field test, and a color vision test to ensure that there are no other abnormalities. Advanced methods like Optical coherence tomography (OCT) and Frequency Doubling Perimetry (FDP) can also be chosen if needed. The examiner must be skilled in selecting the most appropriate test.

Differential diagnosis

Before diagnosing Functional vision loss, the patient should be tested to rule out conditions which cause defective vision or even blindness in one or both eyes with normal anterior segment and a normal fundus. Some major conditions that should be considered include:

• Amblyopia- Amblyopia is a condition in which the brain fails to fully process input from one eye and over time favors the other eye and the vision in one become reduced.
• Cortical blindness-Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the brain's occipital cortex.
• Retrobulbar neuritis- Retrobulbar neuritis cause of visual loss with normal fundus but there will be relative afferent pupillary defect (RAPD) and abnormal visually evoked responses.
• Cone dystrophy- Cone dystrophy can cause a blurring of vision, color vision defects and photophobia.
• Chiasmal tumors- In chiasmal tumors, in addition to vision loss, sluggish pupillary reactions and characteristic visual field defects may be noted.

Investigations

Optometrists and ophthalmologists perform a number of tests to determine if a person has a serious vision loss or if they are lying. The types of tests vary depending on the type of vision loss the patient complains.

Bilateral or binocular blindness

The general behavior of the patient is important in this. If the patient easily enters and walks around the exam room without hesitation, it is a sign of malingering. If a person claims he has bilateral visual impairment, the following tests can be done to see if he is lying.

• Eye contact effect- If a patient claims to be completely blind in both eyes and makes eye contact with the examiner, it is definitely a case of malingering.
• Obstructions- Ask the patient to walk through the exam room where there are obstacles such as waste baskets and chairs and observe if they identify and avoid them.
• Looking at hand- Ask the patient to look at their hand. Those who are truly blind will hold out their hand, look at it, and say, "I know where my hand is, but cannot see it," but malingers, without looking at the hand, will assert, "I cannot see it."
• Signature Test- If the patient is asked to sign with a pen and paper, people who are truly blind will sign easily and consistently multiple times, but those who are simulating blindness will generally scribble on the paper.
• Menace test- If the patient closes their eyes when a hand is suddenly waved towards the patient's face, it means that that eye has vision.
• Mirror test- Hold a large mirror in front of you and ask the patient to look into it. Then slowly turn the mirror sideways. If the patient changes their vision according to rotating the mirror, it means they have vision.
• Reading from smallest letter- Start with the smallest line in the eye chart and gradually increase the size of the letters and ask the patient to read them. Also express surprise to the patient at not being able to see the letters even though they are doubled in size. In this way the patient is more likely to read.
• Vision aids- Four lenses with zero power when placed together are given to the patient in a trial frame and say patient that the lenses are special magnifying lenses. If he says any change in vision, he is malingering.
• Near Vision Testing- In general, near vision decreases in proportion to the decrease in distance vision. A large discrepancy between near visual acuity and distance acuity indicates that the problem is not organic.
• Optokinetic response- In this test, the nystagmus movement of the eyes indicates at least 20/400 vision.
• Psychogalvanic test- This test is useful in people who say they can't even see light. The patient is seated in front of a slit lamp and a bright light is suddenly flashed into his eyes. If they blink, it means they see light.

Uniocular blindness or visual impairment

If a person claims that he has defective vision or no vision at all in one eye, if there are no other signs, the following tests can be done to see if he is malingering.

• Relative afferent pupillary defect- If there is no refractive error or media opacity that cause disparity in visual acuity between the two eyes, if true pathology is present, the affected eye will have a Relative afferent pupillary defect.
• Convex Lens Test- Place a weak convex or concave lens (0.25 D) in front of the non-sighted eye and a high-power convex lens (+10 D) in front of the good eye. If the patient can read all the letters far away, it should be understood that their claimed sightless eye has sight.
• Prism base down test- Place a prism upside down in front of the good eye and ask it to look at a distant light source. If the patient admits seeing two lights, it means that both eyes have vision.
• Prism Base Out Test. Ask the patient to look at a light source. A prism of 10 D is then placed in front of the non-sighted eye with base out. Malingering is confirmed if the eye moves inward (brain activity to eliminate diplopia).
• Red-Green Test- Patient is asked to read the red-green duochrome chart after placing a red glass in front of the good eye. If the patient reads all the letters, it means he has good vision in the said defective eye also.
• Cycloplegic test- Cycloplegic test can be used in children those are not myopic. Put a cycloplegic drug in the good eye and saline in the so called blind eye. After accommodation is paralyzed in the good eye, ask the patient to read small near prints with both eyes open.Cycloplegia in the good eye will blur near vision in that eye, so if the patient reads without any discomfort, it means both eyes have good vision.

Visual field defects

If a person claims that he has defective visual field, if there are no other signs, the following tests can be done to see if he is lying.

• Visual field test- Visual field tests including Confrontation testing can be used to rule out defects in the field of vision.

Treatment

Reassurance is the best treatment that can be given for a patient who is diagnosed with functional vision loss. Ask about stress, anxiety, and depression and refer for appropriate psychiatric treatment if needed. It is important to emphasize to the patient that FVL has a good prognosis, thereby increasing the patient's hope and giving the patient a chance for recovery.Cognitive behavioral therapy or pharmaco therapy for psychiatric ailments may be needed sometimes.

Further reading

• Enzenauer, Robert W. (2014). Functional ophthalmic disorders : ocular malingering and visual hysteria. William R., M.D. Morris, Thomas O'Donnell, Jill Montrey. Cham. ISBN 978-3-319-08750-4. OCLC 896824726.