After undergoing an eye examination, your optometrist will issue you an optical prescription which remains valid for a period of two years. You can use your eyeglasses prescription to buy the right prescription lenses. Eyeglasses prescriptions contain a number of abbreviations and are associated with a special jargon. You will need to understand more about what SPH and CYL as well as VA stand for.
It pays to have a good understanding about your eyeglasses prescription. A first look at your prescription for your eyeglasses shows that there are a few numbers for your OS and OD. The OS or oculus sinister refers to your left eye while the OD or oculus dextrus refers to your right eye. In some cases, you will also see a number for your OU which refers to both your eyes.
These numbers tell you how weak or strong your vision is. If the number is large then your eyesight is poor while if the number is small then your vision is not so poor. The numbers that you see in your eyeglasses prescription also include a minus or plus sign. If the number has a plus sign it means that you are farsighted while a negative sign shows that you are nearsighted. These numbers are measured in diopters which is the unit used to measure the focusing power of the lens. The abbreviation for the diopter is D.
When you check your eyeglasses prescription you may see a number like minus one. This shows that you are nearsighted and your vision is only slightly poor. On the other hand if your number is something like minus four and a half then you are suffering from a bad case of nearsightedness. This condition is worse than a nearsighted number of minus one and it can only be corrected if you use thick and very strong lenses.
A number of plus one means that you have a slight problem with farsightedness. If the number is plus five then you have a bad case of farsightedness. Some people suffer from astigmatism. For them, there are three different numbers in their prescription. These numbers are written as S x C x Axis. The S in this case is the spherical part of the eyeglasses prescription and this shows the amount of near or farsightedness that you suffer from.Eyeglasses prescriptions contain many numbers. Typically, the prescription contains a number for your OD. This part of your prescription is considered the sphere of your prescription and refers to whether you are nearsighted or farsighted. As explained earlier, a negative number means that you have a nearsightedness problem while a positive number shows that you are farsighted.
The C is your cylinder or your astigmatism. This number can be positive or negative and is measured in diopters and shows just how bad your astigmatism condition is. If the number is big then you have a serious astigmatism problem.
The Axis number can be any number from zero to one hundred and eighty. This number shows the orientation of your astigmatism problem. Optometrists need to know more than just how bad your astigmatism is because they also need to know where the difference in the curvature occurs. A typical number showing your astigmatism looks like this: -1 + 2.50 x 180. This number reveals that you have one diopter of nearsightedness and 2.50 diopters of astigmatism and an axis of one hundred and eighty degrees.
The eyeglasses prescription also has a number next to the first number and this number refers to the cylinder which is a term that is also used to describe astigmatism. This number shows the difference in curvature and the power between a couple of points on your eye which is separated by ninety degrees.
If you see the letters DS or diopters sphere then this indicates that the correction of your left eye is absolutely spherical and that you do not have an astigmatism problem. This also shows that the cornea of your right eye may be slightly oblong in shape and that the cornea of your left eye is almost absolutely round. Sphere is also used in place of DS.
Your eyeglasses prescription may also include an ADD number which represents the power that has to be added to your distance prescription to correct your vision at close range. Young people’s eyeglasses prescription generally does not include the ADD number. If it is present in their prescription it shows that they need bifocal power to correct their failing ability to focus on things that are near.
When understanding your eyeglasses prescription you will also need to know more about the meaning of abbreviations such as SVD, SVN, PD and Prism. SVD is nothing but Single Vision Distance. SVN refers to Single Vision Near and is used for reading only. PD or Pupillary Distance refers to the distance between the centers of each of your two pupils. Prism is usually not prescribed but if it is prescribed it is used to displace the image in a particular direction for anyone who suffers from crossed-eyes.