Hello, Your grandson's vision will not matter with a monocular microscope
like the Celestron
Advanced Compound Biological 500x Microscope, CI-MI-44104-EE or the Konus
Academy 1000x Biological Microscope, KO-MI-BIO-5325. As he must focus on the microscope
slide he will be able to adjust the focus to what is best for him. If your grandson wants to look at bugs and rocks he should have the Konus
Diamond 20x - 40x Stereoscopical Microscope, KO-MI-5450. The binocular
head has a dioptor adjustment so when he focuses with one eye he can adjust the other eypiece to focus with the other eye.