Flashes of light in the eyes are caused by migraine headaches, the shrinking of the vitreous humor in the eye or a torn retina, says MedicineNet. Most incidences of flashing lights are not serious, but if they are sudden and frequent, the patient should see his eye doctor.
The light flashes that accompany migraines look like jagged lines or heat waves, says MedicineNet. They last between 10 and 20 minutes and are caused when the blood vessels in the eye go into spasm. They may or may not be accompanied by a headache. In that case, the condition is called ophthalmic migraine.
When the vitreous humor, the gel that gives the eyeball its round shape, pulls away from the inside of the eye the patient might see what looks like lightning flashes in his field of vision, says Kellogg Eye Center. He might also see these lights if he's hit in the eye. These lightning flashes are not unusual as a person ages, but it's possible for the vitreous humor to pull away from the retina enough to tear it. This leads to loss of vision if it's not corrected.
Because it is not possible for a layperson to know the cause of the light flashes in his eyes, it is important to have regular check ups with an eye doctor.