THE ILLUSIONS OF IMPERFECT AND OF NORMAL EYESIGHT
P ERSONS with imperfect sight always have illu sions of vision; so do persons with normal sight. But while the illusions of normal sight are an evidence of relaxation, the illusions of imperfect sight are an evidence of strain. Some persons with errors of refraction have few illusions, others have many; because the strain which causes the error of refraction is not the same strain that is responsible for the illusions.
The illusions of imperfect sight may relate to the color, size, location and form of the objects regarded. They may include appearances of things that have no ex istence at all, and various other curious and interesting manifestations.
ILLUSIONS OF COLOR
When a patient regards a black letter and believes it to be grey, yellow, brown, blue, or green, he is suffering from an illusion of color. This phenomenon differs from color-blindness. The color-blind person is unable to differentiate between different colors, usually blue and green, and his inability to do so is constant. The person suffering from an illusion of color does not see the false colors constantly or uniformly. When he looks at the Snellen test card the black letters may appear to him at one time to be grey; but at another moment they may appear to be a shade of yellow, blue, or brown. Some