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How to understand glass prescription?

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Prescription of the eye glasses you wear as prescribed by optometrists or any other eye care professionals such as ophthalmologist and ophthalmic assistant contains all the necessary parameters required for fitting and dispensing a glass by an optician or Optical dispenser. The parameters are understandable to any eye care professionals and meet the requirements of a patient.
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The diopteric power and the axis varies from one patient to another patient. The aim of different powers is to correct refractive errors like Hyperopia, Myopia, Astigmatism and Presbyopia in adult over 40. The power is determined by automated refractometer or manually with the help of Retinoscope or phoropter. Opticians have very less knowledge about the method of prescription. Their job is to decipher the prescription and assemble the frame and lenses together.

Sample of Glass prescription 1
Sample of glass prescription 2

Understanding the prescription:

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Above are the sample of the prescription card format in which the prescription is mostly written so that a dispenser would understand.
O.D means “Ocular Dexter” meaning Right Eye in latin while O.S means “Ocular Sinister”. The term SPH means spherical dioptric power while CYL means Cylindrical dioptric power. The cylindrical power has “AXIS” that ranges from 1º to 180º. Prism is not commonly used in prescription except for the cases where patient has squinting problem. If prism is present, base too should be mentioned. Distance means the power of the distance while near means power for near as the our eye's lens changes focal length from Distance to Near. The Near power when added to distance is termed as addition as shown in the above figure. Near power means, your glasses are bi-focal or progressive. Presence of cylinder power means, you have astigmatism while spherical power denotes you have Myopia or Hypermetropia, Near power means you have Presbyopia or you are Pseudophakic (Artificial lens implant after cataract surgery).

Things that needs to be considered while prescribing glasses:

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  • Give careful consideration to whether the SPH and CYL are positive or negative.
  • A typical single-vision eyeglasses prescription without astigmatism just needs the SPH. You will likewise require your Pupillary Distance (PD), which might be incorporated on your prescription as two numbers; add these numbers together and you have your PD. In the event that your Prescription does exclude your PD, you have a couple of alternatives. In the first place, you can contact your optometrist and they may give it to you. You can likewise go to a neighbourhood optician and have them measure it. Or on the other hand, you can quantify it yourself.
  • On the off chance that a number isn't in the CYL and AXIS spaces, there is no value for either.
  • You will just have an ADD measure in the event that you wear bifocals/progressives.
  • SPH, CYL, and ADD are composed with decimals. In some cases there are no decimal focuses on the prescription. You at that point get the opportunity to include them in. (Case: a SPH composed as "175" is  "1.75" and an ADD composed as "25" would be "2.50.")
  • Once in a while, the presciption won't be written on a genuine network. The numbers will be that as it may, likely be composed by the framework appeared, with OD to finish everything, OS on base, with segments SPH, CYL, AXIS, and so forth.
  • On the off chance that you see the word PLANO in the line of boxes for one eye, you require a "balance lens" for that eye. A balance lens is a non prescription lens; you require one if just a single of your eyes requires vision correction.
  • Last, however not minimum, if both of your eyes have a similar corrections, just a single line of numbers might be your Prescription composed of.

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