Astigmatism has long been a difficult vision problem to correct. Solutions including, glasses, hard contacts and eventually soft lenses offered varying degrees of success in treating the issue. Acuvue advance contacts incorporate the best technology available and finally offer a very good solution.
Astigmatism is an optical defect, wherein vision is blurred due to an inability to create a sharply focused image on the retina at the back of the eye. Actually there are two different focus points.
The cause of this refractive error, is differences in the degree of curvature on different parts of the surface of either the cornea, or lens. These curvatures will differ between the vertical and the horizontal planes, causing different focal points on each plane. The result is an inability to see fine detail, or the appearance of multiple, offset, and overlapping images.
This vision deficiency can be corrected through the wearing of contacts having a compensating optic. These have a toric shaped surface, resembling a section of the surface of an American football. These lenses have two different powers to compensate for the two different focus points.
The first problem encountered in making these types of of corrective lenses was the issue of keeping them in the stable position they needed to be in to compensate for the refractive error. The first solution was a logical one. Use gravity to prevent the lenses from shifting or rotating out of position.
These ballast type lenses were thicker, and therefore heavier at the bottom. This single zone of stability used gravity to keep the heavier bottom down where it belonged. This was not a perfect solution, however. When in a reclining position gravity will actually move it away from its optimum position. So will quick eye movements or body movements. Blinking can also cause the lens to rotate.
Computer models showed that when the eyelids blink and move across thicker parts of a lens friction is created, causing it to be dragged. The thicker bottom edge of ballast type lenses actually increased the rotation problem while blinking. Acuvue then created their Accelerated Stabilization Design. In this design the eyelid interaction with the lens not only does not cause instability, it actually increases stability.
This lens has thin edges all around preventing blinking rotation, plus thicker parts in four areas. These bumps, 2 on each side actually cause the eyelid to squeeze the lens into the proper position with each blink. This occurs no matter the relation to gravity. It works the same while the wearer is on his side or reclining, as while standing.
Another problem associated with ballast stabilized lenses is instability caused with eye movements whether upward, to left or right, or diagonally. Similar issues are encountered with body movement, such as in athletic activity. Gravitational type forces are also created with acceleration. Clinical studies showed that there was 3 times better stability, and quicker correction with the Accelerated Stabilization lenses than with the ballast design.
Correcting astigmatism caused refraction errors was a challenge. Now with Acuvue advance contacts there is finally a satisfactory solution.
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