What Are Sclera Contacts
If you are familiar with traditional contacts you know how they work. They are simply a small sphere of plastic that is worn on the top of your iris. They are usually of a diameter that is around 8 millimeters - slightly smaller than your iris in most cases. Remember that the diamer varis to some extent depending the type of contacts that you have, and this is something that should be also fitter with your eye doctor. There are a lot of different materials that are used for contacts and very common these days are different silicone hydrogel since these have been the most used material ever since the start of contacts. These days there are also contacts that are made of gas permeable materials that are more comfortable to wear since your cornea won't suffer from oxygen deficiency - the cornea has little or no blood vessels because they would interfere with your vision. It relies mostly in getting oxygen from the air around it, although for a shorter time you can do well with regular contacts.
Sclera contacts on the other hand cover a bit more than just your iris, and they are designed to cover your sclera as well - they are strictly designed for cosmetic reasons, even though most people who wear them, tend to notice that they are better in staying on than regular contacts. The reason for this is that there is much more adhesive surface between the lens and your eye making it stick a lot better. There are different categories of sclera lenses and they are typed by the size - or the diameter. Corneo scleral lenses come with a diameter of 12.9mm to 13.5mm which is just a little bit larger than regular contacts. Semi-Scleral contacts are up from 13.6mm to 14.9mm and they already cover a little more than the smallest sclera lenses. Usually you can see mini-scleral lenses worn since they safely cover the whole iris and a little more, so people who wear white sclera lenses usually wear this size to make their eyes completely white and give the appearance of no iris at all. The largest size is simply called scleral and this is from 18.1mm upwards. If you are good at math you will notice that there is a huge difference between the area of the leses between normal contacts and sclera contacts - you don't even have to calculate it with a formula that gives that surface of a sphere, but instead that of a circle. Since in the formula the area is squared, and the diameter is three times more in sclera lenses than regular contacts, the area is going to be nine times more making it a much more stable lens to wear - they won't come out of your eyes.
Where to buy black sclera contact lenses
It is quite common for people to look for these black sclera lenses around halloween as many costumes work great with black eyes. This makes the costume shops a great place to look for these lenses, but you could also look for them online. What you should keep in mind is that when yo purchase contacts from the previously mentioned sources, they could indeed come with a low price tag, but the fitting is not going to be optimal - that is why I would never recommend you to wear these contacts for more than one night to avoid any damage to the cornea. Poorly fitter contacts can cause serious problems, and that is why I recommend to always get your contacts through a doctor - get your eyes measured even for tinted contact lenses!
You might find cheap contact lenses online, and it might be a sensible idea to get them that way, especially when you have some time for the delivery. If you are a bit late for halloween and you need to get them in a few days, I suggest that yo go to the optician and local costume shops to find them. If you already have contacts that have been measured by a professional, feel free to provide those measurements as reference to be sure that you get the perfect fit even for your black sclera contact lenses.