Some Logical facts about EYES

Why do we see spots after looking at a bright light?

Intense light, such as from a flashbulb or uncovered light bulb, can stimulate the retina (the light-sensitive tissue at the back of the eye) to its maximum response. When this occurs, it takes awhile for the retina to "recover." For a short time you are not able to see well, or you may see spots or a dark afterimage.


Is it possible to tell what someone is feeling by looking at only his or her eyes?

The pupil (the black circle in the middle of the colored iris) may indicate what someone is feeling. Several factors determine the size of the pupil. Primarily, the pupils dilate (get bigger) or constrict (get smaller) to control the amount of light that enters the eyes. In addition, emotions can change the size of your pupils. When you experience pleasure, your pupils briefly dilate. Anger and fear can cause the pupils to constrict.

Why does nose run when we cry?

Tears leave the surface of your eye by evaporating or by entering the tear drainage system. A thin tube called the Canaliculus drains the tears from the inner corner of the eyelids down into the nose. Therefore, when your eyes fill with tears, such as when you cry or cut an onion, most of that fluid ends up in your nose.

Why do eyes sometimes look red in a photograph?

If you look directly at the camera during a flash photo, the light from the flash entering your eyes may reflect off the retina, as if reflecting off a mirror. The back of the eye contains many small blood vessels, which give it a reddish appearance. Therefore, the reflected light looks red. To prevent this reflection from ruining their photographs, professional photographers use a flash that is not exactly in line with the camera. Amateur photographers can ask their subjects to look slightly to the side of the camera.

Why does eyelid occasionally twitch uncontrollably?

Sometimes part of your eyelid may twitch for several minutes or hours. An involuntary twitching of a muscle is called Myokymia. Myokymia of the eyelid can occur with stress, lack of sleep or too much caffeine. Occasional twitching of an eyelid usually disappears by itself and does not indicate a serious problem unless it persists or extends to other parts of the face.

Why might looking toward a bright light cause a person to sneeze?

The "Photic sneeze," a sneeze reflex related to bright light, is not completely understood. As bright light stimulates the retina, it most likely stimulates other related parts of the nervous system. Scientists believe that this stimulation causes nasal congestion, producing a sneeze in some people.


Will looking at the sun really hurt eyes?

Occasionally glancing at the sun usually does not harm your eyes. However, staring for several minutes at the sun or a solar eclipse can damage visual cells in the part of the retina that allows us to see fine detail. This kind of injury, called solar retinopathy, can cause a blind spot in the center of the field of vision. Loss of vision in these cases can be temporary but often is permanent.

Why does vision blur underwater?

The surface of the eye bends light rays, focusing them on the retina and enabling us to see clearly. Light rays bend as they pass from air outside the eye to the fluid within the eye.When someone's eyes are open underwater, the density of the water at the surface of the eye is similar to that of the fluid inside the eye. This decreases the ability of the eye to bend light rays to a focus, and vision is blurry. Wearing a diving mask keeps air in front of the eye, which provides an air-fluid difference and enables the diver to see normally.