How dark is the blue? Can anyone see your eyes behind the lenses?

thansk for asking, for the blue mirrored lenses, nobody can see your eyes behind the lenses. I hope this helps.

“can you use these on rimless silhouette frame(prescribed eye glasses)?”

Hello , Have a nice day, and thank you for reaching out. Yes, this clip on sunglasses can be used for rimless glasses, but you need to find the suitable size To better help you with this, I will need more information about your frames, and I also need to know the frames height and full frames width(I suggest you to use a ruler to get the measurements). If possible please kindly send me at least 1 picture of your frames, this will help me make the correct advice. If there's anything else about the product, please feel free to let me know, and I will always be here to listen to and help you. Sincerely, Chaingo Customer Support

are glasse good over reading glasses?

Yes, that's for sure, but before you place the order, please check out the size chart and size suggestions first, I hope you can find the one that will best fit for your reading frames.

Are these helpful for older people who are extremely sensitive to sunlight?

thanks for asking, please try with the selection of category 4 lenses, these are super dark selection, light transmission rate no larger than 8% (regular sunglasses lens light transmission rate is usually 15%), and before buy, please confirm that the selection of the size is good for your frames. Please follow the measuring instruction in the 4th picture. I hope this helps, and if you have any other questions, please feel free to let me know. Aaron