I'll add a bit on the HI vs VI.
For most people who wear glasses / contact lenses (50% of adults) their sight with glasses is very close to normal sight. The problem with most people's eyes is the shape of the eyeball and a lense (from glasses) in front means that the light hitting the back of the eye is the same as for someone with a normally shaped eye ball.
If a VI is caused by something like nerve damage, a brain tumour, missing eye ball, damaged retina etc etc then glasses may improve vision but will not correct it.
A hearing aid is not the same as glasses, it doesn't change the signal reaching the ear, it just amplifies it and it also amplifies everythng else. So if you have normal hearing you can filter out certain sounds such as, if you are in a noisy cafe, you can still have a conversation with someone next to you, but if you wear a hearing aid all the other conversations are amplified making it harder to hear.
Additionally HI is not usually caused by the signal (sound) hitting the wrong place or not being focussed - if it is, it is the kind of temporary deafness you get with an infection or a cold.
So the ability to hear is dependent on the workings of the inner ear and the nerves/brain. The inner ear is much more complex than an eyeball in terms of engineering.
In short, for most people who wear glasses their sight is corrected to normal, for most people using a hearing aid their hearing is not corrected to normal or near normal.