Functional Visual Loss

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Disease Entity

Functional Visual Loss is a decrease in visual acuity and/or visual field not caused by any organic lesion. It is therefore also called non-organic visual loss.

Disease

Functional Visual Loss (FVL) is a decrease in visual acuity and/or visual field not caused by any organic lesion. It is therefore also called non-organic visual loss. FVL cannot be explained by organic pathology after a complete neuro-ophthalmic examination. The decrease in visual acuity may involve one or both eyes and may vary from mild blurriness to complete blindness. The visual field defects may affect one or both eyes. They may include constricted or tunnel visual fields, hemianopias, etc. FVL is commonly associated with concurrent diagnoses of depression, anxiety, panic attacks, and fibromyalgia. FVL is diagnosed frequently in the neuro-ophthalmologist's office, though less common to the general ophthalmologist.

Etiology

Functional visual loss (FVL) runs the spectrum from the malingerer (to feign for gain) to subconscious visual loss caused by underlying psychological disorders in the patient. Dr. Stanley Thompson provided an excellent description of this spectrum of functional patients (1). At one end is the "deliberate malingerer" who is faking visual loss to gain disability, benefits, attention, etc. Next is the "worried imposter" who knows he is exaggerating his visual symptoms but is actually worried that he may have a serious visual problem. He does not want to miss out on future benefits. Then there is the "impressionable exaggerator" who feels sure something is very wrong with his eyes and is determined not to hide the signs of his illness. He wants to help the doctor by making the disease easily recognizable. And finally there is the "suggestible innocent", who has convinced himself, often after some trivial injury, that one eye is blind or that he has tunnel vision, although he seems strangely complacent about it. FVL has long been considered a prototype of conversion disorder (2). Subconscious visual loss at this side of the spectrum is commonly associated with concurrent diagnoses of depression, anxiety, panic attacks, and fibromyalgia. Kathol et al (2) found that psychiatric disorders are present in over 50% of patients with FVL.

Risk Factors

Functional visual loss (FVL) is commonly associated with concurrent diagnoses of depression, anxiety, panic attacks, and fibromyalgia.

Pathophysiology

See Etiology

Diagnosis

The key to diagnosing Functional Visual Loss is to first complete a full, dilated eye examination to rule out organic causes of visual loss such as refractive error, dry eye, cataract, uveitis, maculopathy, etc. What you will find are inconsistencies in your exam. Finding that are inconsistent or that don't make sense. Why does this patient have count fingers vision in one eye and no relative afferent pupil? Why did the patient see 20/70 for the technician, but sees 20/30 when repeated by me, with encouragement? Your goal is to prove and document better vision than alleged.

Classic findings:

  1. Tunnelling of confrontational visual field or tangent screen.
  2. Spiralling, Crossing, or Stacking of isopters on Goldmann visual field.
  3. Cloverleaf pattern on automated visual field.

History

Probe into the history of the patient looking for a past medical history of depression, anxiety, panic attacks, and fibromyalgia. Try to pin down the details of the onset of visual loss. Usually this information is sketchy, having gradually started a few days, weeks, or months ago. In adults, there may be a trivial injury that started the process. In children, there may have been a psychosocial event that acted as a trigger (3).

Physical examination

1. Visual Acuity (VA): your goal is to document good visual acuity in both eyes. An automated refractor can sometimes help in discovering uncorrected refractive errors. If the visual acuity is still decreased, I like to use the bottom-up technique for checking VA. Start with the 20/20 line and go up instead of the opposite. Give lots of encouragement and tell the patient that you are going to make the print larger and easier to read: move to the 20/25 line, etc. Other physicians use slick techniques of fogging the better eye in the phoropter to prove better vision in the functional eye. Also check Near VA to look for inconsistencies. The mirror test and OKN drum are good ways to look for gross vision when the patient claims to be blind. A large hand-held mirror seduces the patient into looking and following his facial features. The standard OKN drum induces optokinetic nystagmus and corresponds to 20/400 vision.

2. Visual Field (VF): Always do confrontational visual fields in these patients. Commonly, you will see constricted fields. If this occurs, move back from 1 meter to 2 meters to check for tunnelling of the visual field. Remember that the normal visual field is a funnel, not a tunnel. The VF should expand as you go farther from the eye.

An automated visual field may commonly show constriction which may be confused with glaucoma or retinitis pigmentosa. A hemianopia may also be seen respecting the vertical midline, which will need to be differentiated from a central nervous system process. Frequently, the VF has low reliability indices which is consistent with FVL. Also a cloverleaf pattern may be seen which is helpful in making the diagnosis of FVL. I recommend ordering a Goldmann VF in these patients.

The Goldmann VF (GVF) is done by a technician with the patient. The tech is able to perform the GVF at the patient's speed and with encouragement. Three classic findings on GVF of FVL include 1) generalized constriction with stacking of the isopters, 2)crossing of the isopters which is illogical, and 3) spiraling of the isopters, which is also illogical. These findings, in concert with the rest of the exam, help pin down the diagnosis.

3. Motility: When a patient has repeatedly demonstrated constricted VF on your exam, you can trick them into offering proof of their normal peripheral VF by checking saccades. Tell them that you are checking the speed of their eye movements. With their eyes fixated on your nose, have them saccade to your fingers placed nonverbally to the far left and right. Also carefully observe how the patient ambulates into and out of the exam lane as well as how easily they find your hand to shake. They usually have no difficulty. Remember to document these inconsistencies in your exam.

4. The pupil exam must be performed and documented well. Pupil size, reactivity, and the presence or absence of a relative afferent pupillary defect (RAPD) is paramount. It is an objective measure in the exam, unlike VA and VF which can be subjective.

Management

General treatment

Simple reassurance of a normal eye exam is an effective treatment. Around the year 1900, Babinski stated that functional manifestations were caused by suggestion and could be cured by persuasion. This is a simple and sensible rule (1). Remember to stress a good prognosis, thereby providing a way out for the patient: "Most people with this kind of trouble find that their vision gradually gets better, and I expect the same for you."

Remember to stay calm and do not confront the patient concerning his inconsistencies on exam. Do not get into a shouting match which would not help the patient or the doctor.

Follow-up appointments are important to document improvement as well as to look for co-existent organic disease.

Ask about underlying stress, anxiety, and depression. If the patient desires, refer for appropriate psychologic treatment. When the patient accepts that stress, anxiety, and depression can indeed be the cause of his or her problem, he or she can begin to regain the lost vision (3).

Medical follow up

Follow-up appointments are important to document improvement as well as to look for co-existent organic disease.

Prognosis

Remember to stress a good prognosis, thereby providing a way out for the patient: "Most people with this kind of trouble find that their vision gradually gets better, and I expect the same for you." Normalization of visual function occurs in a majority of patients (3).

Additional Resources 

References

1. Thompson HS. Functional Visual Loss. Amer J Ophthalmol. 1985;100:209-13.

2. Kathol RG, Cox TA, Corbett JJ et al. Functional Visual Loss: II. Psychiatric aspects in 42 patients followed for 4 years. Psychological Med. 1983;13:315-24.

3. Lim SA, Siatkowski RM, Farris BK. Functional Visual Loss in Adults and Children. Patient Characteristics, Management, and Outcomes. Ophthalmol. 2005;112:1821-8.

Original article contributed by: Joseph G. Chacko, MD
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