Functional Visual Loss Flashcards
(42 cards)
What is functional (non-organic) visual loss?
Is a condition in which a patient complains of visual disturbances not explained by pathology of ocular structures and the visual system
What is organic (non-functional) visual loss?
Visual loss due to ocular pathology
How do we differentiate between functional and organic (non-functional) visual loss?
- Difficult
- No objective pathology
- Not a diagnosis of exclusion
- Need positive findings of ‘functional’ to support diagnosis
- Diagnosis = Possible functional element/ functional overlay
Need to ensure not meeting a subtle, treatable organic pathology
What are the 3 forms of functional visual loss?
- Malingering
- Factitious disorders
- Somatoform disorders
What is Malingering?
- Purposeful feigning of symptoms
- Usually for clear secondary gain
e.g. Student claiming visual loss to get out of exams or have time off school
How often is Malingering seen and who is it more common in?
- 1-5% children
- 5.25% adults
- Most common in females
- More common aged 11 - 20yo
What is Factitious Disorder?
- Intentionally produced symptoms
- Assuming the sick role
e.g. person claiming visual loss and wanting to be registered blind - No specific gain
Why might someone pretend to have visual loss (Factitious Disorder)?
- High incidence of concomitant psychosocial events >1/3 (Lim et al, 2005)
- Cry for help
- Attention
- Other problems
What is Somatoform Disorder?
- Occurs outside the persons conscious awareness
- Not intentional
- Psychological / psychiatric problems (Hysteria)
- Psychogenic visual loss (often complex psychiatric and medical conditions)
Person unaware of why they have visual symptom, no secondary gain, not wanting to be ‘ill’, suspicion of psychological disorder and/or underlying psychiatric problem. Can be subconscious expression of stress, emotional or psychological problems.
What is Functional Overlay?
True visual loss as a result of an organic disease/process but is exaggerated or intentionally claims symptoms are worse often to be believed or to provoke investigations
What are common claims of someone with functional visual loss?
- Reduced Vision or blind in either or both eyes
- Visual Field Loss
- Loss of stereopsis
- Convergence or Accommodation Defect
- Difficulty Reading
- Colour Vision Defects
- Photophobia
- Polyopia or Diplopia
- Strabismus
- Night Blindness
- Flashes
- Headache
- Eye Pain
What must we consider when testing for functional visual loss?
- Order of Tests & Test Selection
- Observation
- Phrasing
What should you observe for in a patient with functional visual loss?
Observe the patient before you call them in…
- Are they on their phone, Facebook? Whatsapp?
- Standard web print on a mobile device is 14px/10.5pt
When you call their name how do they respond?
- Do they look up and make eye contact?
- Pick up their jacket? Water bottle? Put their phone in away?
- Fold up the newspaper?
In The Clinic:
Do they navigate to your clinic room and find the chair?
- Is this overly dramatic?
- How are their relatives reacting?
A truly blind patient will move cautiously and bump into objects naturally. A functionally blind patient will deliberately bump into objects or exaggerate movements.
Put your hand out to shake their hand
- Do they see and find your hand easily?
Pass them something, do they take it?
What is the sunglasses sign in functional visual loss?
The “sunglasses sign” in a patient without an obvious ophthalmic reason to wear sunglasses is highly suggestive of nonorganic visual loss.
How do you investigate functional visual loss during a case history?
- Plausible
- Realistically fit e.g. Trauma
- Current circumstances and past events e.g. Delve deeper
- FH
- Previous medical records
- OH e.g. amblyopia, cataracts, myopia
They may say that they have always had a ‘weaker eye’
Prescription in each lens identical? May indicate a balance lens and so longstanding poor VA (as the poorer eye is blind or too weak/not used so put in a balanced lens)
Can ring opticians and ask re previous VAs
Check for retinal detachment signs or age-related macular degeneration (e.g. a sudden drop in vision and/or distortion meaning straight lines will appear bent)
Need to check glasses are correct, up-to-date, their own and made-up correctly
What Proprioceptive tests can we use for investigating functional visual loss?
- Finger Touch Test
- Signature Test
The fingertip touching test is performed by asking the patient to bring their index fingers together. A truly blind patient can easily touch the tips of the fingers together. Those who are functionally blind tend not to. Do it BEO and monocularly.
Similarly, the signature test is also a non-visual task. A patient with organic visual loss can easily sign his/her name without difficulty, but a FVL patient may produce a bizarre signature.
Can be done both eyes open or if uniocular VA loss each eye at a time – compare the two.
What is the Startle test when investigating functional visual loss?
- Flick fingers
- Flash brightest light
See patient’s reaction to see if they can see the target coming towards them
What is the Mirror Test in Functional Visual Loss?
Surprise them with a mirror and then rock it back and forwards to see if their eyes track in line with the mirror movement
How can we use colour vision to test for functional visual loss?
Ishihara screening plate - Would expect even people with colour deficiency to do the screening plate well
What does Optokinetic response tell us in functional visual loss?
OKN Drum, Flag, mobile app
Saccade to fix and then track slow pursuit and then saccade – if you see a OKN response you can expect the vision to be in the region of: 20/200 (6/60)
If a patient claims not to see the top line of a VA chart what can we do to test for functional visual loss?
- Changing test distance (x2 or ½)
- Changing charts
- Numbers & letters
- Monocular & binocular
- Encouragement
- Extra time
- Bribery
- Wait
How can we use VA tests to investigate functional visual loss?
We can use the Keeler Crowded (3m) to repeat their vision (without the ETDRS chart present)
- No frame of reference
- Different testing distance
- Start at -0.300 and work up
Is the result the same?
If the vision has been tested on the same chart it is quite easy to stop in the same place each time i.e. 3rd row down.
If non-functional = no difference between the two tests i.e. this and an ETDRS
If functional = difference between them
How do you approach testing VA again in a patient suspected of functional visual loss?
That they should now be able to see it –
“This test is closer, so it should make it easier for you”
“that was a bit hard let me try an easier test closer up”.
Start from the highest acuity (smallest letters) and work backwards
When approach normal/expected level of vision
“These are getting larger now you’ll probably be able to make them out”
Encouragement!
“You’re doing extremely well, keep trying”
How can we use VA testing in functional visual loss that isn’t just VA charts?
Also can use neutralising lenses, rotating high cyl lenses and small vertical prism
For Unilateral VA loss use the:
- Cylinder Test
- Fogging Test
Say: “I think this lens could be of some help to you, can you now read this line of letters”
