The reason of eye defects are varied from different eye defects. For example, If you suffered from Hypermetropia, some people also called it long-sightedness. And it can happen when the lens is unable to thicken sufficiently. Besides, myopia is also a common eye defects for most of people. And most people called it nearsightedness, is a condition in which the light rays are focused in front of the retinal surface. The lens of the eyes can focus close objects, but can't focus distance objects. And these eye defects can be corrected by eyeglasses.
In most cases, this can be caused by glaucoma, cataracts and some other eye diseases. People who have got these diseases are usually very sensitive to light rays. In terms of this, you had better keep wearing your sunglasses or your special glasses all the time so that you can avoid your eyes being hurt. Never ignore your any eye detects because maybe one day they will get you myopia and even sometimes get you to go blind. Sounds horrible, huh? You had better go to your eye doctor to have your eyes checked regularly.