Flashes and Flickers
What causes it?
Flashes and flickers occur from inappropriate activation of the retinal photoreceptors or the vision-related cerebral cortex.
The major cause of inappropriate photoreceptor activation is tugging by an aging vitreous. In late middle age, the vitreous normally detaches from the retina. As it does, it tugs on the retina and stimulates photoreceptors. The patient sees flashes of light especially with sudden eye movement.
Rarely the detaching vitreous tears a hole in the retina. In most cases, the retinal hole seals spontaneously. But sometimes liquid vitreous seeps into the hole and causes a retinal detachment. To see how vitreous detachment may lead to retinal detachment, click here.
The flashes of vitreous tugging usually go away within days. Persistent flickering is more likely to be caused by inflammation, ischemia, or inherited degenerations of the photoreceptors.
Inappropriate activation of vision-related cerebral cortex is caused mainly by migraine, but vertebrobasilar ischemia and occipital seizures may also do it.
Migraine produces a zigzag flicker that expands across the hemifield in 20 minutes. By contrast, the flickering of seizures and ischemia is usually stationary. To see what migraine looks like, click here.
Here are some other facts you should know about migraine:
- Migraine with visual aura is a wave of cerebral excitation and depression that spreads across occipital cortex. Its genesis is uncertain.
- The first migraine episode typically occurs in adolescence or early adulthood, but it may not occur until late adulthood. Headache usually follows the visual hallucination. The hallucination may occur without headache, especially in older adults. When the migraine aura is stripped of headache, the condition is called "acephalgic migraine" or "migraine equivalent."
- As a cause of transient visual hallucinations, the diagnosis of migraine should not be made unless the typical features are present because alternative causesseizure and ischemiamust be evaluated and treated.
What to do?
If you suspect retinal photoreceptor discharge, refer for prompt ophthalmologic examination. If you suspect vision-related cerebral cortex discharge and cannot confidently diagnose migraine, refer for ophthalmologic or neurologic examination.