By Eddy Montilla.
There is a layer of tissue at the back of the eye called retina, which is sensitive to light and this creates nerve impulses that, via the optic nerve, go to the brain where a visual image is formed. The retina not only responds to light, but pressure too. Flashes and lights in your range of vision might be associated with head migraine, but in general, “the stars” you see after a sneeze or a cough, the round beam of light you see when you rub your closed eyes and other luminous visions are the result of pressure that stimulates the cells of the retina. The technical term to explain this, that is, the experience of seeing light when, in fact, light has not entered your eyes is phosphene. You may also see stars if you stand up quickly because this action reduces the flow of blood to the brain and when low blood pressure occurs, your brain is deprived of oxygen, which affects your eyes or parts connected to them. Most of these visions are common and harmless. Other visions, however, might be dangerous. For example, I remember that my father “saw stars” one day when my younger sister showed him her credit card bill and told him: “Daddy, help me!”
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