- drug toxicity
- migraine headache
- thyroid ophthalmopathy
- arteriovenous malformations
- seizures
- psychiatric disorders.
Digoxin, cocaine, paclitaxel, and clomiphene may have ocular side effects, including photopsia. The first symptoms of digitalis toxicity often are visual and include photopsia, yellow or green discoloration of the visual field, halos, and the appearance of frost over objects.5 Signs of cocaine intoxication can include visual hallucinations such as photopsia, shadows, moving objects, and insects crawling and co-occurring euphoria, hypervigilance, impaired judgment, and autonomic changes such as tachycardia, pupillary dilation, hypertension, and nausea.6 High-dose paclitaxel infusion has been reported to cause photopsia.7 Clomiphene can cause flickering lights and shimmering that persists after discontinuing the medication.8
Migraine with aura, which includes photopsia 39% of the time,9 often involves an expanding central visual disturbance or scotoma, and usually is confined to 1 visual field but may involve both. The aura typically lasts 10 to 20 minutes and often is followed by headache. Patients often report a history of episodic stereotyped auras and headache. Ocular examination is normal.
Ophthalmic migraine, also known as ocular or retinal migraine, is thought to be caused by transient vasospasm of the choroidal or retinal arteries and can be precipitated by postural changes, exercise, and oral contraceptives. It manifests as a gradual visual disturbance in a mosaic scotomata pattern that enlarges, producing total unilateral visual loss lasting from minutes to an hour, and—misleadingly—can be associated with minimal or no headache. Ocular examination is normal, and a personal or family history of migraine confirms the diagnosis.
Seizure activity in the occipital cortex and adjacent association areas can produce static light and stars. In a prospective study of 18 patients with occipital epilepsy, visual seizures lasted from a few seconds to 3 minutes—although rarely 20 to 150 minutes—and occurred in multiple clusters a day or week.10 All but 2 patients had secondary generalized tonic-clonic convulsions. Occipital seizures often are misdiagnosed as the visual aura of migraine, particularly when elementary visual hallucinations are followed by post-ictal headache and vomiting.11 Lights with a color or a spherical shape suggest occipital epilepsy. Consider ordering an electroencephalogram (EEG) if the clinical diagnosis is unclear.
EXAMINATION: No obvious cause
During a mental status exam, Ms. G is pleasant, cooperative, alert, and oriented to person, place, and time. Her speech is fluent, her affect is full, and she describes her mood as a “sensitive, overwhelmed state.” Her thoughts occasionally are tangential, and she perseverates on guilty, embarrassed, and paranoid thoughts. She has auditory hallucinations and experiences photopsia during the interview, but denies other visual hallucinations. She shows no deficits in attention, concentration, memory, language, calculations, visuospatial abilities, or general fund of knowledge.
Her physical exam shows pupils that are equal, round, and reactive to light with normal extraocular movements, intact visual fields, 20/20 visual acuity in both eyes with glasses, and sharp optic disc margins with no retinal abnormalities apparent on funduscopic exam. The rest of her physical and neurologic exam is normal. Her complete blood count, electrolytes, kidney, liver function tests, urinalysis, and serum toxicology screens are normal. She has no history of immunodeficiency.
An MRI performed a year earlier showed mild diffuse congestion of a left maxillary sinus but no other intracranial abnormalities, and a waking EEG with sphenoidal electrodes was normal.
The authors’ observations
Evaluation of patients with photopsia includes taking a history and performing an eye examination including visual acuity testing, visual field testing, and funduscopic examination. The appearance, location, and duration of photopsia may help narrow the differential diagnosis and identify emergent cases (Table 1 and Table 2). Seizure activity associated with flashing lights suggests occipital epilepsy. A history of hypertension, diabetes, or polymyalgia rheumatica points to vascular causes, and hyperthyroidism suggests that flashing lights may be phosphenes of Graves’ disease. Myopia or eye trauma could indicate vitreous traction. Prescription medications and illicit drug use may point to a toxic etiology.12
Table 1
Diagnoses suggested by photopsia phenomena
| Feature | Suggested diagnosis |
|---|---|
| Appearance | |
| Twinkling lights with grey spots | Emboli |
| Zigzag lines | Occipital epilepsy |
| White flashes | Vitreous traction on the retina |
| Flickering lights and shimmering | Clomiphene use |
| Temporally located flashes of light, floaters, or blurred vision that is worse in dim illumination | Posterior vitreous detachment and retinal tearing |
| Location | |
| Temporal | Migraine or retinal pathology |
| Central | Occipital lesion or embolus |
| Monocular | Retinal pathology |
| Binocular | Cerebral cause |
| Duration | |
| Lightning quick | Vitreous detachment |
| Lasts up to 30 minutes | Migraine or occipital epilepsy |
Table 2
Photopsia differential diagnosis: Look for co-occurring symptoms
| Co-occurring symptoms | Suggests |
|---|---|
| Seizure activity associated with flashing lights | Occipital epilepsy |
| Yellow or green discoloration to the visual field, halos, and appearance of frost over objects | Digitalis toxicity |
| Shadows, moving objects, and insects crawling with co-occurring euphoria, hypervigilance, impaired judgment, and autonomic changes such as tachycardia, pupillary dilation, hypertension, and nausea | Cocaine intoxication |
| Floaters, or a ‘curtain’ or ‘shadow’ moving over the visual field, which may be accompanied by central or peripheral vision loss | Retinal detachment |
| Bilateral blurred vision, ataxia, vertigo, dysarthria, or drop attacks | Vertebrobasilar artery insufficiency |