Your glasses have not changed their prescription in twenty years. You have seen just fine with these same prescription lenses all along. Then, all of a sudden, you cannot look at things up close; everything blurs and makes you feel like you are going cross-eyed trying to look at what is right in front of you.
What is going on? Your optometrist cannot find anything really wrong with your eyes, either -- at least not from the usual set of vision tests. Is it your glasses? Is there something wrong with your eyes? Maybe it is something completely different than what you may have expected:
You, and Your Eyes, Are Getting Old
If you wore glasses most of your life, you can definitely expect to wear bifocals when you get much older. If you never wore glasses, you can also expect to wear bifocals at some point. The human eyes are not designed to work the same way forever; in fact, the lenses in the human eye and the muscles that control the lenses deteriorate over time. Somewhere in your mid-forties to early fifties you will begin to notice that your up-close vision is just...weird. Describe what you are experiencing to your optometrist; there is a very good chance that you need new glasses with bifocal lenses.
Your Vision Is Improving
Oh, if only this could happen to everyone! After years of wearing corrective lenses so that you can see, your vision begins to improve. You find you can see better without your glasses than with them. This is an exceedingly rare situation, but it could still be the reason why your near vision goes blurry when you are wearing your glasses. Only your optometrist can tell for sure, so schedule an appointment as soon as possible.
You Are Developing Cataracts
Cataracts are a terrifying thing; essentially, the lenses in your eyes cloud over to the point that you become blind, or you can only see moving shadows in place of people, colors, and things. If you are developing cataracts, you can tell as well as your optometrist can.
Just use a camera with a flash on it and take a picture of yourself staring straight into the camera. If you end up with pictures that look like you have the eyes of a ghost (i.e., your eyes are reflected as white or yellowish spheres in the picture), you are developing cataracts. Thankfully, your optometrist can not only diagnose and confirm that fact, but he/she can also refer you to an ophthalmologist for surgery to replace the cataracts with new lenses.
For more information, contact companies like Vision Eyeland Super Optical LLC.