People normally need glasses because of the shape and size of their eye. Exercises won’t help this.
Although you may not be able to see very well with them and may get a headache or double vision, you won’t come to any harm from wearing glasses that are not your prescription (unless you’re driving a motor vehicle).
The membrane that covers the white of your eye (the conjunctiva) also lines your eyelids, so it is impossible for a contact lens to get lost behind your eyes.
Reading in dim light or in the dark is highly unlikely to cause any permanent damage to your eyes, but it could cause eye strain which can be uncomfortable. Your eyes adjust to the light around them and your pupils enlarge in order to collect the most light. We are designed to see detail better [...]