Astigmatism is a very common form of refractive error (incorrect vision) among customers in UAE, Saudi Arabia, USA and Europe. Similar to other body parts like ears, hands or feet, the eyes are not fully symmetrical but can vary slightly in shape. Tthe clear surface of the eyeball which is called cornea is not 100% symmetrical but slightly shaped similar to a rugby ball (toric in shape) or in some cases has an irregular shape in general from birth or after an injury. Simply put, the need for correction is for some areas of the eye stronger than for the rest of the eye.
What is the difference of a spherical contact lens and a toric contact lens for astigmatism?
Due to the irregular shape of the eyeball, the varying correction throughout the lens has to be always aligned relatively to the required correction in each area of the eyeball. While spherical contact lenses can turn freely in the eye, toric contact lenses need to be always aligned in the same direction and should not rotate as this would cause an incorrect vision correction while the lens is not in place.
This can be achieved by manufacturing the toric contact lens slightly thicker and heavier in the bottom. Due to the higher weight in the bottom of the lens, the lens will always align itself on the cornea and will maintain it’s direction similar to a pendulum.
How to read an astigmatism prescription for toric contact lenses?
A contact lens prescription for the correction of nearsighted astigmatism, for example, could be: -2.50 -1.00 x 90.
The first number (-2.50) stands for the Sphere power for the correction of myopia in the flatter (less nearsighted) part of the eye.
The second number (-1.00) stands for the Cylinder power of the additional myopia (nearsightedness) correction required for the more curved part of the eye. In this case, the total correction required for this area (also called meridian) is -3.50 D (-2.50 + -1.00 = -3.50 D)
The third number (90) is called the Axis. This is the location (in degrees) of the flatter area of the eye, on a 180-degree scale where 90 degrees designates the vertical axis of the eye, and 180 degrees designates the horizontal axis.
Optometrists in Dubai, Abu Dhabi, Riyadh and Jeddah will usually provide a complete rx prescription including sphere, cylinder, axis as well as base curve of the required lenses.
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