Here is some info dealing with some of the familiar eye conditions that may cause you to need prescription spectacles

Myopia – Also known as short sightedness, near sightedness

Shortsighted people generally visualize well up close, but not at a distance. Distant objects seem blurred, while near objects are in focus.

DESCRIPTION

The eyeball is longer than usual, making the eye "too powerful." The image is focused at a point in front of the retina. The greater the degree of myopia, the closer the distance at which the Shortsighted can visualize clearly.

SOLUTION

Myopia can be corrected with a concave lens which is thinner in the center and thicker at the border. This type of lens system pushes the focus back onto the retina and restores good vision at any distance.

HYPEROPIA – May be known by the terms long sightedness, far sightedness

Farsighted people focus a lot better at a distance compared with close up. Although distant objects are properly focused, the accommodation required to focus on nearby objects causes eyestrain.

DESCRIPTION

The eyeball is shorter than normal which means the eye is not powerful enough. The eye is said to be "too short" and the image is focused behind the retina.

SOLUTION

Hyperopia is corrected using a convex lens which is thin at the edge and thick in the centre. This type of lens system brings the focus forward to the retina.

ASTIGMATISM

People with astigmatism have poor nearby and distant vision. They do not comprehend the contrasts between horizontal, vertical and diagonal lines in the same way as the rest of us.

Astigmatism is always accompanied by another visual impairment, such as Myopia, hyperopia and Presbyopia.

DESCRIPTION

Astigmatism is usually caused by an irregularly-shaped cornea that is slightly oval, rather than round, and oblong rather than spherical.

SOLUTION

Astigmatism can usually be corrected with a cylindrical lens system whose curvature offsets the corneal irregularity.