An eyeglass prescription usually provides a pair of numbers. Representing Sniper Vision System Review the left and right eyes, the two numbers are respectively abbreviated to OS and OD. These two numbers can be either positive or negative. A positive number indicates farsightedness while a negative one signifies nearsightedness. In detail, positive numbers have a plus mark and negative ones are prefixed with a minus mark.
In some cases, only two numbers are not enough. An eyeglass prescription for astigmatism has three numbers. Two of them are the same as a normal prescription and the third one stands for the severity of astigmatism. A larger number indicates more serious astigmatism. Furthermore, the third number is between zero and one hundred and eighty, showing the location of astigmatism. This location information is necessary for eye doctors to make proper lenses with appropriate vision correction. Each of the numbers being either whole numbers or fractional ones should be described precisely. Only accurate numbers can ensure proper vision correction for individuals.
Another number that may affect corrective properties of eyeglasses is the pupillary distance PD, which indicates the distance between the two pupils. This number is necessary if one person contemplates ordering prescription glasses online. Some eyeglasses imprint the PD number on the frame. Without an old pair of glasses, the PD number can be easily measured using a ruler and a mirror. Remember to measure distance between the centers of the two pupils.
When we have some eye problems, we will have to wear some sort of lenses, either glasses or contacts. The maintenance of glasses is very easy, whereas contacts are very troublesome. Particularly, we have to clean those lenses all the time, so as to prevent any possible infections. However, these lenses must be cleaned in some specific solutions which can be obtained from some optical stores. If we do no wear them, these lenses should be put into these solutions. Doing so can lengthen the longevity of our lenses.
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