To decide whether non-prescription glasses are bad for your health, you first need to consider which definition of "non prescription glasses" you are using. This particular term is used in two different ways. It can mean "fake" or fashion glasses, which do not have corrective lenses; they are similar to normal sunglasses, except they are not shaded. The second definition of "non-prescription glasses" means that they are vision-correcting glasses that were accepted without a prescription.
If you are using the first definition, and want to go shopping for fashion glasses that have no corrective properties, then you will be perfectly fine, as they will not damage your eyes at all. After all, people have worn sunglasses for many years without ill effects, and of course sunglasses may also protect your eyes from damaging ultraviolet rays, depending on which ones you buy. The main danger for people who wear non-prescription fashion glasses appears when vanity overrides sanity. It is ill-advised to drive at night or in dull conditions wearing dark sunglasses, and although there is no danger to your eyesight from wearing the glasses, you are at increased risk of having an accident due to reduced visibility.
A little care needs to be taken if you are going to wear the corrective type of non-prescription glasses. If the wrong strength of lenses is selected, the result can be eyestrain and associated headaches, and over a period of time this can cause damage to the eyes.
If you suffer from presbyopia – a condition involving the deterioration of eyesight due to aging – you will be more likely to benefit from cheaper non prescription reading glasses. However, it is still important to go to a reputable store, such as a pharmacy, where you will be able to try a wide selection of glasses of varying strengths. Once you have found the optimal strength of lenses, you will be able to pick out a pair in a style of your choosing.
For people younger than 40 years old, and particularly in cases where blurred vision develops rapidly, or is accompanied by other symptoms such as headaches, it is vitally important to see an optician or optometrist in the first instance. There are well documented cases where people have developed vision problems, to find that the underlying cause was a more serious health condition. Eye specialists are trained to spot these problems – although in the vast majority of cases, the cause of the vision defect will be normal and benign.
Some of the possible health conditions that have been noted to affect vision include diabetes, where rapidly changing blood sugar levels can affect the quantity of fluid in the eyes, causing swelling which results in distortion of vision. Another, potentially fatal, condition is extreme hypertension which can lead to heart attacks and strokes. Such an underlying problem may be spotted by an optometrist because it can lead to swelling of the optical disk. Even brain tumors have been identified by eye specialists during examinations for the cause of blurred or double vision.
So to answer the question whether non-prescription glasses are bad for your health, in general they are not. If you are healthy and are positive you do not have any under medical conditions, they will be perfectly fine. However, all cases where there is a sudden change in your eyesight should be investigated by an expert to rule out anything more serious than a vision defect. In general, once you have been prescribed your first pair of corrective glasses, usually fairly early in life for shortsightedness, it is recommended that you see an optician for a retest every two years. If you are over 40 years old, though, and your sight has slowly deteriorated over a long period, then non-glasses will be fine, although there is no reason to avoid seeing a specialist if you are concerned about any other accompanying symptoms.