If you have been wearing glasses for most of your life, think back to when you first got them. Were you in grade school? Perhaps you only got them as an adult. Regardless of how old you were when you first started wearing glasses, do you remember what prompted the need for you to wear them? Many children will not complain that they can not see the black board in school, and it is usually the teacher who notices a student's behavior changing or grades slipping before a parent does. The teacher will usually pass along any observations to the parents and the first step is usually an eye exam, resulting in prescription glasses.

For children, it's common for optometrists and ophthalmologists to prescribe prescription glasses for distance vision. Even if a child has a minimal prescription need, adding glasses will drastically improve their mood, attitude, and performance at school. As we grow older, our eyes change and our vision care needs also change. When you hit age 40, you may notice that seeing up close has become difficult. This creates a need for an entirely new prescription and you may be required to wear reading glasses.

Once you understand the two most common types of glasses – distance and reading correction – you're halfway to understanding your vision care needs. Distance correction needs are the most commonly prescribed glasses prescription on the market. If you take a look at your prescription, you'll see distance needs noted by a minus sign in front of a number in the sphere (SPH). The higher the number in minus, the more correction is needed. Alternatively, reading prescriptions are usually noted with a plus sign in front of a number in the sphere. It's not common for reading prescriptions to reach high digits past +6.00.

Once you've been diagnosed with a need for both reading and distance correction, you will be given a third prescription and things get a little tricky. You'll have a prescription for reading and distance correction as well as a prescription that combines the two if you wish to purchase multifocal lenses like progressives or bifocals. Your prescription will also note two different pupal distances – one for distance and one for reading. The reading pupil distance is usually three millimeters less than the PD for distance correction. Your prescription for bifocal or progressive lenses will also include what's called an ADD or additional value – sometimes called near vision. It's a number denoted with a plus sign in front of it and can often change the plus or minus sign in front of your sphere. The ADD usually runs from +0.25 to +4.00 – the higher the ADD, the more likely it is to change the value in the sphere.

Now you probably understand the three reasons for needing glasses. There's an additional reason and it's for astigmatism correction. If you've noticed your eyes still becoming blurry even after getting new glasses, there may be a refractive problem in your eyes – commonly referred to as astigmatism. If you have astigmatism and need correction, it will be noted on your eyeglasses prescription under the cylinder (CYL) and axis. The cylinder will tell your optician how sever the correction is and the axis will tell him or her the degree of refraction correction needed on a plan of 0 to 180. You may not need distance or reading correction but you may need astigmatism correction – which will still lead you to wearing prescription glasses. Regardless of your need, it's important to wear your glasses as prescribed by your doctor – your eye health depends on it.