Edited Invalid date
15.12 Defects in Vision
The human eye has many processing mechanisms.
The movement of the image is needed for human vision.
In the process of viewing an object, the eye can execute small rapid movements, 30 to 70 per second, which change the position of the image on the retina.
It is possible to counteract the eye movement under experimental conditions.
The person's image gradually fades under these conditions.
The first two defects can be explained by looking at the image of parallel light by the eye.
The normal eye focuses light onto the retina.
The lens system focuses the light in front of the eye's retina.
This misfocusing is usually caused by an eyeball that is too large.
There is light behind the eye.
The eyeball that is shorter than normal is the cause of the problem.
The hyperopic eye can accommodate objects, but they are farther away than normal.
There are two defects that can be summarized as follows.
There is a defect in the eye.
An ellipse-shaped eye cannot form sharp images of two parallel lines because it is more curved along one plane than the other.
One of the lines is out of focus.
All three defects can be corrected by placing a lens in front of the eye.
A diverging lens is needed to compensate for the excess refraction in the eye.
The focusing power of the eye is improved by a converging lens.
A cylindrical lens is used to focus light on one axis but not on the other.
Review flashcards and saved quizzes
Getting your flashcards
Privacy & Terms