Let's start with something easy: the difference between nearsightedness and farsightedness. Nearsightedness, also called myopia, is a refractive error in the eye which results in the ability to see things in focus up close but blurry from afar. In lay terms, you can't see objects in the distance but you can see them up close. Farsightedness, on the other hand, is also known as hyperopia, long-sightedness, and hypermetropia. It's another refractive error in the eye that results in the inability to see things clearly up-close but crisp and clear from afar. It's the opposite of nearsightedness - so you'll have problems seeing things up close but no problem seeing things in the distance.
Another optical term that is often misunderstood is the word diopter. It's a fairly simple term and actually a term that indicates measurement. In quick terms, a diopter is the unit of measurement that tells you the power of your lens. For example, if your right eye has a sphere of -4.00, that means that you have four diopters of power in your right lens.
Base curve is another term that confuses people and it's a fairly easy term to understand! In lay terms, it's the front curve of your lens. In olden days, it was the curve from which all other curves were measured. Astigmatism is another term that sounds funky but is actually easy to understand. If you're diagnosed with astigmatism, rest easy - it's a common problem that affects most people who wear glasses. All it means is your cornea is misshapen which causes light to enter into your eye and focus on to a few points instead of one. It causes blurriness and some discomfort but it's nothing to worry about. In your prescription, your cylinder (CYL) and axis will indicate whether or not you need astigmatism correction.
Has your doctor ever recommended aspheric lenses? That term can sound like something out of a comic book but it really only means that he's suggesting lenses that are not perfectly round. Since traditional lenses have a surface that resembles that of a basketball (totally round), aspheric lenses gradually change in curvature as you get away from the center of the lens - it's not round. This type of lens is actually really popular in high index lenses and is also changing the way people wear prescription glasses.
Visiting your eye doctor shouldn't leave you feeling like you're on a quiz show. When you turn to buying eye glasses online, some of these term-clarifications will make that experience go smoothly. These definitions should leave you feeling more relaxed and at ease during your next appointment to get your eyeglasses prescription.