Loss of vision. Malingerers frequently are involved with an insurance claim or are looking for other forms of financial gain. Those with psychogenic visual loss truly believe they have lost vision.
No ocular or neuro-ophthalmic findings that would account for the decreased vision. Normal pupillary light reaction.
Amblyopia: Poor vision in one eye since childhood, rarely both eyes. Patient often has strabismus or anisometropia. Vision is no worse than counting fingers, especially in the temporal periphery of an amblyopic eye. See 8.5, Amblyopia.
Cortical blindness: Bilateral complete or severe visual loss with normal pupils. See 10.24, Cortical Blindness.
Retrobulbar optic neuritis: Afferent pupillary defect and dyschromatopsia are present. See 10.14, Optic Neuritis.
Cone–rod or cone dystrophy: Positive family history, decreased color vision, abnormal results on dark adaptation studies, and multifocal ERG. See 11.29, Cone Dystrophies.
Chiasmal tumor: Visual loss may precede optic atrophy. Pupils usually react sluggishly to light, and an afferent pupillary defect is often present. Visual fields are abnormal.
Cancer-associated retinopathy or melanoma-associated retinopathy: Immune-mediated attack of photoreceptors. Fundus often appears normal. Abnormal macular optical coherence tomography (OCT) and ERG.
The following tests may be used to diagnose a patient with nonphysiologic visual loss (to prove the malingerer or hysteric can see better than he or she admits).
Two “codes” are used to test patients feigning decreased vision in the list below:
Patients Claiming No Light Perception
Determine each pupil’s reaction to light (U or B): The presence of a normal pupillary reaction suggests that anterior visual pathways are intact, but does not prove nonphysiologic visual loss (pupillary response is maintained in cortical blindness). When only one eye has no light perception, that pupil will not react to light. The pupil should not appear dilated unless the patient has bilateral lack of light perception or third cranial nerve involvement. If a patient responds aversely to light stimulus, one can establish some level of afferent input.
Patients Claiming Counting Fingers to No Light Perception
Test for an afferent pupillary defect (U): A defect should be present in unilateral or asymmetric visual loss to this degree.
Mirror test (U or B): Cover the better-seeing eye if monocular visual loss; with bilateral complaints leave both eyes open. Slowly tilt a large mirror from side to side in front of the patient’s eyes, holding it beyond their range of hand motion vision. If the eyes move in the same direction of the mirror, the patient can see better than hand motion.
Optokinetic test (U or B): Cover the better-seeing eye if monocular visual loss. Ask the patient to look straight ahead and slowly move an optokinetic tape in front of the eyes (or rotate an optokinetic drum). If nystagmus can be elicited, vision is better than 20/400. Patients can suppress this ocular response by focusing past the drum.
Base-out prism test (U): Place a 4- to 6-diopter prism base-out in front of the supposedly poorly seeing eye. If there is an inward shift of the eye (or a convergent movement of the opposite eye), this indicates vision better than what the patient claims.
Vertical prism dissociation test (U): Hold a 4-diopter prism base-down or base-up in front of the supposedly good-seeing eye. If the patient sees two separate images (one above another), this suggests nearly symmetric vision in both eyes.
Worth four-dot test (U): Place red-green glasses on patient and quickly turn on four-dot pattern and ask the patient how many dots are seen. If the patient closes one eye (cheating), try reversing the glasses and repeating test. If all four dots are seen, vision is better than hand motion.
Stereo-acuity testing (U or B): Both eyes open, check stereo. If able to see 9/9 Wirt circles, vision is likely 20/40 or better in each eye.
Patients Claiming 20/40 to 20/400 Vision
Test near vision (U or B): If normal near vision can be documented, nonphysiologic visual loss or myopia has been documented.
Retest distance visual acuity (U or B): Start with the 20/10 line and ask the patient to read it. When the patient claims inability to read it, look amazed and then offer reassurance. Inform the patient you will go to a larger line and show the 20/15 line. Again, force the patient to work to see this line. Slowly proceed up the chart, asking the patient to read each line as you pass it (including three or four different 20/20 lines). It may help to express disbelief that the patient cannot read such large letters. By the time the 20/30 or 20/40 lines are reached, the patient may in fact read some letters correctly. The visual acuity can then be recorded.
Fog test (U): Dial the patient’s refractive correction into the phoropter. Add +4.00 to the normally seeing eye. Put the patient in the phoropter with both eyes open. Tell the patient to use both eyes to read each line, starting at the 20/15 line and working up the chart slowly, as described previously. Record visual acuity with both eyes open (this should be visual acuity of supposedly poorly seeing eye) and document the vision of the “good eye” through the +4.00 lens to prove the vision obtained was from the “bad eye.”
Retest visual acuity at 10 feet from the chart (U or B): Vision should be twice as good (e.g., a patient with 20/100 vision at 20 feet should read 20/50 at 10 feet). If it is better than expected, record the better vision. If the vision is worse, this suggests nonphysiologic visual loss.
Visual field testing (U or B): Goldmann visual field tests often reveal inconsistent responses and nonphysiologic field losses.
Accusatory statements may impact rapport and are best avoided. Instead, patients may be reassured of their normal examinations and likelihood of visual recovery. When documenting, it is often advisable to objectively record the normal findings and lack of pathology rather than to explicitly state that the patient has nonphysiologic/functional vision loss.
Referral to mental health professionals should be considered when appropriate.