Nonphysiologic Visual Loss
Patients may present with complaints that mimic organic disease but are factitious. The diagnosis requires demonstrating normal or better than stated visual function. Furthermore, it is important to perform the relevant investigations to exclude serious organic diseases. Several diseases are often misdiagnosed as nonphysiologic and should be kept in mind when considering this diagnosis, including
• early cone dystrophy or Stargardt’s disease
• bilateral occipital lobe infarcts
• pituitary tumors
• keratoconus
• retinitis pigmentosa, especially sine pigmento
• cancer-associated retinopathy/melanomaassociated retinopathy
The most frequently encountered forms of these disorders involve the afferent visual system and consist of the following:
• No vision (one or both eyes)
• Decreased vision (one or both eyes)
• Visual field loss (one or both eyes)
NO VISION
No vision is often the easiest to detect. The examiner has to prove that any vision exists in the purported blind eye(s). This can be accomplished by one of several methods.
• Mobility testing: Watch the patient enter the room and perform manual tasks. Patients with nonphysiologic visual loss often claim to be unable to perform any tasks of mobility but can navigate around obstacles placed in their path.
• Functional tests: A blind person will be able to sign his or her name without difficulty. A patient with feigned visual loss may claim to have difficulty doing this.
• Outstretch arm-to-nose test: A blind person will be able to easily touch their nose after the arm has been extended; whereas a person with feigned visual loss, not realizing this is a proprioceptive and not a visual test, may miss his or her nose completely.
• Threat: A sudden threatening movement toward the patient’s face that causes him or her to react appropriately proves the existence of vision.
• Mirror test: Hold a mirror up to the blind eye(s) and ask the patient to concentrate on focusing straight ahead. Then, tilt the mirror horizontally and vertically. The more the patient tries to steady the eye, the more it will move in concert with the mirror tilt.
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