The human eye also belongs to a relatively small group that is equipped to identify different colours. Most insects, fish, birds and many animals can only distinguish different shades and textures. The basis of colour sense is the mixture of three transparent colours — red, green and blue. When they are combined in the correct intensities they make up white. People with a well-developed colour sense can recognize many hues of the same colour, perhaps even as many as a hundred. But colour sense is highly variable, and it is estimated that one male in eight is `colour-blind‘; that is to say, Read the rest of this entry »
The results of these preventive measures were disappointing. Some observers reported a slight decrease in the percentage of myopia in schools in which the prescribed reforms had been made, but on the whole the injurious effects of the educational process were not eliminated to any extent.
Further study of the subject has only added to its difficulty, while at the same time it has tended to relieve the schools of much of the responsibility ‘formerly attributed to them for the production of myopia. As the American Encyclopedia of Ophthalmology points out, “the theory that myopia is due to close work aggravated by town life and badly lighted rooms is gradually giving ground before statistics.” Read the rest of this entry »
A shortsighted young woman, to take the opposite of this case, had a passion for mathematics and anatomy and excelled in those subjects. She learned to use the ophthalmoscope as easily as the farsighted girl had learned Latin. Almost immediately she saw the optic nerve and noted that the center was whiter than the periphery. She saw the light-colored lines, the arteries; and the darker ones, the veins; and she saw the light streaks on the blood vessels. Some specialists never become able to do this, and no one could do it without normal vision. Her vision, therefore, must have been temporarily normal when she did it. Her vision for figures, although not normal, was better than for letters. Read the rest of this entry »
