Most of the people on the globe use prescription glasses for correcting their impaired vision. Though there are many advanced techniques like laser surgery for permanently removing this impairment, still people feel to be convenient with the prescription glasses than the contact lens. These prescription glasses are available online and from those online stores you can get the eyeglass as per your prescription to your door step with much care. They are also cheap and are available in large. While ordering prescription eyeglasses online the customer need to specify the PD which expands as pupillary distance. It is the distance between the two pupils of the eyes and this is very important for grinding the prescription glasses and for choosing the frame length. While buying from the shops the ophthalmologist will himself check the PD and make a lens as per the measured figures and at no cost that information will be relayed to you. And if you need the PD alone he may charge a huge amount. What i wanna tell is to buy a device that checks the PD of your eyes at home and so you can buy a prescription eyeglasses of your choice from famous online shops like Zenni.