Q. How far can the human eye see?
A. "There's no limit to how far a person can see," Said Dr. Merton Flom of the College of Optometry at the University of Houston. "What determines how far you can see is the amount of light ultimately can be detected. Some stars we see aren't there right now, but the light from millions of years ago is still traveling to us."Sharpness of vision, or visual acuity, has nothing to do with how far you can see, Flom added.
According to the 1994 edition of "The Guinness Book of World Records," in 1984, Dr. Dennis Levi, also of Houston's College of Optometry, repeatedly identified the relative position of a thin, bright-green line within 0.85 seconds of arc (1 second of arc is 1/3 600th of 1 degree of a 360-degree circle). What Levi saw is equivalent to picking up light movement of 1/4 inch at a distance of 1 mile.
A visual acuity of 20.200 is considered legally blind. This means the person can see an object at only 20 feet that a normal eye can see at 200 feet.
"We try to adjust the vision to 20/20, which is what the normal eye sees, " said Dr.Kyle Cook from Master Eye Associates in Arlington, Texas. "I've only seen three people who have tested at 20/5, which is roughly three lines better than the smallest line on the eye chart, and they all were pilots."
Q. Do fishes have all five senses?
A. Most fishes have six senses that are well adapted for an aquatic environment. They use their sense of hearing, touch, smell and sight for detecting predatory and prey. They have taste buds, but scientists haven't conducted many studies on taste perception. Fishes also have a lateral line down the side of their bodies that senses vibrations in the water. Sharks have an electromagnetic sensory system around their heads, giving them a seventh sense.