Most of us at age fifty are wearing a progressive pair of lenses or maybe a line bifocal. These are designed for distance viewing, which is usually a good eight feet or further, and the bottom part is designed for reading at approximately sixteen inches.
This creates a problem when trying to read music, which is usually at a distance anywhere from twenty-two to twenty-eight inches away. There is no distinct focal point for this distance; thus, you are not able to read your music clearly. Many people try to lift their heads to read through the bifocal area. There is a little bit of power for that distance, but it is too small to accurately see the full sheet of music.
So, here are two ways of fixing this problem. The first is simply using a clip-on magnifier where you would clip it onto your present glasses. When it is in place the power of the clip-on would be the extra power needed on top of the distance window to read the music at the required distance. The only measurement needed for this is the distance from eye to music stand and the appropriate power can be added for this distance.
The second way of fixing this problem is to make a second pair of glasses where the top part of the lens (or full lens if you want to use modified reading glasses) is designed to read the music. Again, the measured distance from eye to music stand is required so that the appropriate power can be designed.
Your optometrist would be able to create a prescription for you, based on the distance you would provide, your age and the prescription you are wearing now. The one downside with this design is that any correction designed for the music stand means your distance vision is now blurred. Thus, looking at the conductor would not be clear with a pair that are specifically made for the music stand distance. However, with the clip-on device you can flip it up and then use your normal distance power of your own glasses to see the conductor and further away.
There is no one pair of glasses that will allow you to see both the distance and your music clearly, because you have to look through the top half of the glasses to see both targets and you need two different powers to see each one.
These are two solutions that will work so that you are able to read your music clearly because anything else will not provide clear vision over the whole page of music.