Vision 101

The Human Eye

Anatomy of the eye
A human eye gives the sharpest vision when it is perfectly spherical, that is, round like a basketball. Distortion occurs when the eyeball is too short from front to back (Hyperopia) or too long (Myopia), or the curvature of the cornea is irregular, egg shaped rather than a perfect sphere (astigmatism).

Vision 101

How the eye works
Light from object A is focused by the cornea and crystalline lens to form an upside-down image on the light-sensitive cells of the retina. Information is transmitted as impulses from these cells to the brain via the optic nerve. The quantity of light entering the eye is regulated by the iris. The pupil is the variable-sized black circular opening in the center of the iris.

Astigmatism

Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. The surface of the cornea is toric, oblong in shape like a football, instead of perfectly round like a basketball. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance. Consequently, vision is blurred at most distances.

Astigmatism is usually hereditary, although factors, such as low light levels and too much work done close up can contribute. Over time this condition may increase slowly, but generally over a lifetime it remains relatively stable. Forty-five percent of people who require vision correction have some degree of astigmatism. Symptoms include squinting, occasional headaches and eye strain. In most cases, astigmatism is accompanied by myopia (nearsightedness) or hyperopia (farsightedness).

Here’s how a toric lens corrects astigmatism.


The irregular shape of an astigmatic eye cornea and/or lens produces two focusing points in front of or behind the retina in blurred vision.	A toric lens corrects the refractive errors, creating a single focal point in the retina where vision is sharpest.

For the past two decades, millions who have an astigmatism believed they could never wear soft contact lenses. And, many who were fitted with toric lenses for astigmatism often found the performance unsatisfactory.

At Kontur, toric lenses have always been our specialty. In fact, our late founder, Dr. David Ewell, invented the toric design in the 1970s that almost all toric labs use today. Many patients that were told that they could not wear soft torics have been successfully fit with Kontur Toric lenses.

So, if you were told you couldn't wear torics, we invite you to try the toric that practitioners use "when all others fail"!

Nearsighted vision (myopia)

A nearsighted eye sees near objects within a certain range very clearly while distance vision appears blurry at all times. An estimated 70 million people in the U.S suffer from this condition. Most often caused when the eyeball is too long for the focusing power of the lens and cornea, nearsightedness creates an overpowered eye which causes images to reach true focus in front of the retina. Correction requires a "minus" lens to "weaken" the eye optically to permit clear distance vision.

Here's how a spherical contact lens corrects nearsightedness.

The shape of a nearsighted eye focuses images in front of the retina, producing a blurred distance vision. By reducing the cornea's focusing power, a spherical contact lens creates a single focal point on the retina where vision is sharpest.