This is probably one of the most commonly asked questions regarding contact lenses. Those that do not wear them regularly see contacts as a mere commodity.
In the United States contact lenses are labeled as a medical device, and are therefor regulated by the food and drug administration. They are not medical devices because they provide a vision correction, but rather because they rest directly on the eye and become part of the entire ocular system.
When used properly, contact lenses are amazingly safe. However, when used improperly they pose serious health risks. Contacts have been known to cause serious infections, the most extreme of which can cause permanent loss of vision.
Therefor, the answer to the question is that you must be fit properly for any contact lens by a licensed eye care provider. Even if they are strictly for cosmetics, such as Halloween contact lenses.
Before you get discouraged, you should know that it is incredibly easy to be fit with lenses. Simply visit your local eye care provider and let them know what you are interested in. They will give you a thorough eye exam to ensure you can safely wear lenses. This probably will take less than 10 minutes. And hopefully your exam will prove that your eyes are healthy and free of glaucoma or other silent thieves of sight.
Next, your eye care provider will take a few simple measurements for contact lenses. Contact lens measurements are quick and painless. If you so desire, your eye care provider can get lenses for you, or you can order them elsewhere. Some offices are very thorough and will ensure you are comfortable inserting and removing your lenses. And most importantly, taking care of them.
When you actually purchase your lenses, all you need are the specifications of your prescribed lenses and the name of the eye doctor who prescribed them.
You should be very careful to purchase your Halloween lenses from a reputable supplier. Never buy contact lenses from untrusted sources, such as a gas station or flea market. If you have any doubt about the source of your contact lenses, just ask your eye care provider. They have just as much interest in your eyes staying healthy as you do.
In summary, you will need to visit an eye care provider to wear contact lenses, even if they are just for cosmetics. Keep in mind it is a simple and affordable process that is in place to ensure your safety and health.