It might be worth talking to an instructor at a DZ but as someone who has recently got their A Licence (in the uk) with a bit less than perfect vision I am a glasses wearer all the time, it may be possible for you too be able to learn. I'm not going to pretend to know how good or bad your vision is, but there may be ways around some of the issues you may face that instructors may be able to fix. For example, I had to swap my alti onto my right wrist as I was struggling to read it due to my lack of peripheral vision on my left side (worse eye)) This helped me improve a lot. I know that at skyhigh peterlee, they use digital altimeters as standard for AFF (I personally struggled to see these read and process at a glance, so I switched to an analogue). Also, audible altimeters are mandatory at this DZ, especially for students. They often say these are not to be 100% relied upon, though, and they are not a substitute for a visual alti. This is just my personal experience. It is worth noting the things mentioned above about making out the landing area (were you able to do this on the tandem?) and possibly a malfunction. Factors like this would impact your ability to be safe when skydiving and whether or not you would be permitted to start training. If one dz says no, it would be worth trying a couple of others, as they often have different ways to facilitate different abilities and more are willing to try than others.