Jose Hernandez, age 7, of Visalia, Calif., for his question:
WHO INVENTED EYEGLASSES?
Medical experts say that when eyeglasses are well fitted, they can correct most vision defects in healthy eyes. But if they are not measured exactly to correct the deficiency of each eye, they can cause blurred vision and a great deal of discomfort. They must be fitted by skilled people and must be changed when the eyes change their focusing power.
Eyeglasses are instruments which aid people with imperfect vision. Glasses are made of two lenses mounted in a frame so that one lens is in front of each eye. The two lenses help focus light rays so that they will fall properly on the retina and form a clear image.
History shows that eyeglasses go back into ancient tines. Doctors today, however, say that they doubt if the early glasses were very helpful.
We don't know exactly who invented glasses or spectacles, as they were often called. In his book "Opus Maius" published in 1267, Roger Bacon included information about spectacles so we know they were widely used then.
The Chinese are said to have actually invented glasses long before they came into use in Europe. According to one legend, they were used as early as 500 B.C. Also, Marco Polo reported that he saw many Chinese wearing glasses in China about A.D. 1275.
During the Middle Ages, crude glasses were sold by peddlers on the streets of many European cities. These glasses were often worn for ornament and sometimes fitted. so badly that they did more harm than good to the person wearing them.
Benjamin Franklin invented bifocal glasses to save the trouble of changing his glasses when looking from near objects to distant ones. Each bifocal lens had parts of two different lenses, each having its own focusing powers.
In the 1700s eyeglasses improved greatly when the grinding of lenses was first based on the principles of light refraction, or the way light rays are bent when they travel through glass.
Lots of people wear glasses today to help them do close work, such as reading.
Farsightedness happens when a person can see distant objects but cannot focus on close objects. The inability to focus on rays which come from distant objects is called nearsightedness.
Some people7have imperfections in the curvature of their corneas. Rays which pass through the eye will not focus properly, bring a condition called astigmatism. This condition can be corrected by a tonic lens in glasses. This lens compensates for variations in curvature.
Lenses are also available today that fit directly over the eyeballs, beneath the eyelids. These are called contact lenses.