visual illusions caused by ocular disease include haloes around lights from acute glaucoma or cataracts and metamorphopsia from macular disease. A very common simple visual hallucination is the sensation of flashes of white light from posterior vitreous detachment or retinal tear. Patients with bilateral (and, occasionally, unilateral) poor vision from any cause often experience simple or complex visual hallucinations (Charles Bonnet syndrome). A rare retinal cause of simple visual hallucinations is cancer-associated retinopathy, resulting in intrusive colored flashes

compression of an optic nerve by an orbital or brain tumor can cause the simple hallucination of flashes or sparkles of white or colored light. Patients with optic neuritis or anterior ischemic optic neuropathy (AION) may have similar complaints

by far the most common visual phenomenon of brain disease is the simple visual hallucination of migraine. Rarer and more serious disease such as tumors affecting the higher visual areas can present first to ophthalmologists with strange-sounding visual illusions (e.g. a viewed object stays in vision even when the patient looks away; moving objects look stationary or leave a blurred or multiple-image trail; objects look distorted or warped; double or multiple images are seen with each eye). Brain tumors, metabolic disease or dementia can also result in complex visual hallucinations (e.g. seeing flowers, animals, monsters, people who aren’t really there). Patients with focal brain lesions causing visual illusions or hallucinations often have hemianopic visual field defects detectable on perimetry, and the illusions or hallucinations are in the hemifield with the defect

although patients with psychiatric illnesses may have visual hallucinations, such patients believe that what they are seeing is REAL, whereas patients with hallucinations from eye or brain disease usually know that what they are seeing is NOT REAL!

what exactly is the patient seeing?

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  detailed description

  
  
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  one or both eyes?

  
  
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  where in the visual field (all over, central, to the side)?

  
  
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  when did it start?

  
  
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  speed of onset?

  
  
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  development over time?

  
  
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  has it stopped now?

  
  
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  is it getting better, staying the same or still worsening?

  
  
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  transient visual loss?

other ophthalmic symptoms: is the vision otherwise normal or is there also blurred vision, field loss or double vision?

neurologic symptoms, e.g. headaches, numbness, weakness, memory loss, personality change?

previous medical and surgical history: cancer, dementia, potentially toxic medications?

social history: smoker, alcohol, illicit drugs?

if patient over 50: symptoms of giant cell arteritis (GCA)?

system review questions: any clues to the cause anywhere in the body?

visual acuity

color vision testing

visual field defect to confrontation?

eye movements

pupils

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  relative afferent pupillary defect (RAPD)?

  
  
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  anisocoria?

eyelids: ptosis?

orbits

decreased corneal or facial sensation to light touch?

orbicularis and facial strength?

if patient over 50: palpate temporal arteries

measure blood pressure: in all cases, especially if disc swelling is present

full neurologic examination: in all cases of unexplained visual phenomena