An eyeglass prescription or RX issued by an eyeglass prescriber after an eye examination is necessary when buying prescription glasses.
Eyeglass prescriptions vary but typically include the patient's name, power of the lenses, prism, pupillary distance, expiration date, and the prescriber's signature.
To read or understand an eyeglass prescription can get complicated if you don't know optical knowledge and the abbreviations well. 
*Click here to get the guide of how to read prescription.
To get your glasses prescription, you need to make an appointment with your eye care provider or local vision center for an eye exam, and they will issue it for you. 
Don't forget to double-check if there's a PD measurement on your prescription. 
*Click here to know how to measure your PD.