Your eye is a complex system of multiple layers of material with different refractive indexes, all trying to project the great big wide world onto your tiny retina. Sometimes there is a mismatch between the refraction of light into the eye and its length, and the focusing system at the front of the eye misses its target in the back. This causes near-sightedness or far-sightedness, which is not a medical disease in and of itself, but just a description of your refractive state not being perfect.
There are medical conditions that can accelerate near-sightedness or far-sightedness progression, so please see an optometrist or other medical doctor for an exam to be sure you don't have any medical issues. Just like you'd get your kid checked out if he was a little short for his age, but just focus on healthy lifestyle choices if his health was otherwise good.
If your vision problems are entirely due to refractive state, your doctor will probably prescribe glasses that give a 20/20 correction. At the point that you've been medically cleared and have a prescription you are ready to start the EM method.