Colored contact lenses for Halloween: what to know first

Toward the end of October the shops fill up with pumpkins and paper bats, and costumes start appearing on the streets after dark. Somewhere between choosing an outfit and planning the makeup, plenty of people decide to change their eye color as well. Lenses that turn the iris red, gold or ghostly white, give you cat's eyes, or make the eyes look bigger have become very easy to buy.

When I worked behind the counter of an optical shop, this time of year always brought the same question from customers who had never worn contacts: "If there's no prescription in them, they're harmless, right?" My answer never changed. With or without a prescription, a lens sits directly on your eye, and the same care applies.

Below are the questions I heard most often at the counter, with the answers I wish everyone had before a costume party.

If the lenses have no prescription, do I still need an eye exam?

Yes. Colored and cosmetic lenses are medical devices, just like lenses that correct vision. Japan has regulated them in the same strict category as corrective lenses since 2009. In the United States, all contact lenses, including purely decorative ones, require a valid prescription, and sellers are not supposed to supply them without one. Many other countries have similar rules.

There is a good reason for this. A contact lens rests on the cornea, the clear dome over the colored part of your eye. The cornea has no blood vessels and gets much of its oxygen from the air, through the tear film. A lens partly covers it. If the curve or diameter of the lens doesn't suit your eye, it can slide around and rub the surface, or cling so tightly that tears can't move underneath.

A "no prescription" lens is simply one where the power reads zero. The base curve and diameter still vary from product to product, so zero power does not mean the lens fits everyone. Customers were often surprised to hear that.

At a fitting, the eye doctor or optometrist checks the cornea and the conjunctiva (the thin clear layer over the white of the eye) for scratches or inflammation, looks at your tears and measures the curve of your eye. From that they decide whether contacts are safe for you right now and which kind is likely to fit. Some people with dry eye or allergies are better off without lenses for a while. Oddly enough, people with perfect eyesight who have never needed an eye exam often gain the most from that first look.

If you have never had one, the guide to your first eye exam explains what happens on the day and what to bring. Book it well ahead of the party, not on the afternoon itself.

When you buy, use a seller who asks for your prescription. Lenses sold at costume stores, market stalls, beauty counters or websites that never ask about your eyes are a warning sign.

Can I borrow a pair from a friend, or share mine?

No. When everyone gets ready together, someone always has a spare pair, or wants to try yours "just for a minute." Please say no.

There are two reasons. Eyes differ in size and curve, so a lens that fits your friend may not fit you. And a lens that has been in someone's eye carries their tears, residue and the bacteria that live around their eyes. Put it in yours and you introduce germs your eyes have never met.

The same thinking applies to buying a new pair of the same product just because it suits a friend. Online reviews are no better. Someone else's comfort tells you nothing about how a lens will sit on your eye.

And don't wear daily disposable lenses a second time to save money. Even if you keep them overnight in solution, they are not made to be reused.

Does the color or size of the lens make a difference?

Colored lenses have tint or a pattern added to part of the lens. Depending on the product, the pigment may sit close to the surface or be sealed inside the material, and you can't tell by looking what the side touching your eye is like.

The material, the thickness and how much of the lens is tinted all affect how much oxygen gets through and how comfortable it feels. A vivid color, or a lens that makes the iris look bigger, is not gentler on the eye. Looks tell you nothing about safety, and which product suits your eyes is a question for the eye doctor once they have examined you.

Vision is another issue. Pupils widen in the dark, and with some lenses the tinted ring can then overlap the pupil and make things harder to see at night or in a dim venue. Costume parties are usually dark. Take extra care on stairs, when crossing the road and on a bicycle, and if your vision feels off, don't drive.

How long can I wear them on the night?

There is no single safe number of hours. Follow the wearing time for that product and whatever your eye doctor told you. If you don't normally wear contacts, your eyes are not used to them, so start with shorter periods.

Don't make the party the first time you put them in. Within the limits your eye doctor gives you, practice at home for a short time a few days earlier so you know how to put them in and take them out. Beginners tend to poke at the eye and rub it when a lens won't settle, and the rushed half hour before you leave the house is exactly when eyes get scratched. If a lens slides out of place and you can't find it, don't keep digging with a fingertip. If it stays stuck, have an eye doctor remove it.

Halloween nights also run long. You start getting ready in the late afternoon, take photos, move to a second venue, and suddenly it is past midnight. Crowds, heated rooms and dry night air all dry the eyes as the hours pass.

Pack a small pouch before you go:

• a lens case and fresh solution, if your lenses are the reusable kind
• your glasses, if you normally wear them

Decide in advance what time the lenses come out, note when you put them in, and set an alarm on your phone if it helps. Take them out somewhere you can wash your hands.

Never sleep in them. Nodding off on the train home, or falling asleep on the sofa still in costume, is the classic Halloween mistake. Think of taking the lenses out as the last part of the costume.

What about glitter, eyeliner and costume makeup?

Costume makeup puts far more color and powder around the eyes than everyday makeup. With lenses, what matters is the order you do things in and keeping particles out of your eyes.

• Wash your hands with soap and dry them well before touching a lens.
• Put the lenses in first, then do your makeup.
• At the end of the night, take the lenses out first, then remove the makeup.
• Keep glitter, shimmer and loose powder modest, and away from where it can fall into the eye.
• Don't draw liner on the waterline, the inner rim of the eyelid inside the lashes.
• Close your eyes before using hairspray or setting spray.

A fleck of glitter trapped under a lens scrapes the cornea every time you blink. If your eye suddenly feels gritty or starts streaming, don't rub. Wash your hands and take the lens out. If the feeling stays after the lens is out, have an eye doctor look at it.

Take makeup off gently, letting a remover soften it rather than scrubbing at the lids. When you get home tired late at night, the temptation is to wash your face first. Keep to the order anyway.

Not all stage makeup and face paint is meant for use near the eyes. Check the label before you put a product close to the lid margin, and skip anything without that guidance or that you haven't tried on your skin before.

My eye hurts and it's red. What now?

Take the lens out straight away if you notice any of these:

• pain or stinging
• redness in the white of the eye
• tears that won't stop, or more discharge than usual
• light so uncomfortable you can't keep your eye open
• blurred or hazy vision

Even if the eye feels better once the lens is out, don't put it back in that night. If pain or blurring continues, see an eye doctor the same day. A lens can scratch the cornea and let infection in, and a serious corneal infection can leave lasting damage to sight. A little improvement is not a reason to keep waiting.

Bring the lenses in their case, along with the packaging, so the doctor can see exactly what you were wearing. Be ready to say when you put them in, how long you wore them and what makeup you used.

While you wait, avoid the things that feel helpful but can make matters worse: rubbing, borrowing someone else's eye drops, and rinsing or storing lenses in tap water, which can carry organisms such as acanthamoeba that cause serious infections in lens wearers. Wear glasses, and rest your eyes.

Most eye clinics are closed late on Halloween night. If you have severe pain, vision that is getting worse, or an eye you can't open, go to an emergency department or call your local emergency number (such as 911, 999, 112, or 119 in Japan). The page on eye emergencies and first aid lists the symptoms that can't wait and what to do in the meantime.

After the party

Once the lenses are out, pay attention to how your eyes feel that night and the next morning. If redness or discomfort is still there the following day, see an eye doctor soon. Problems caught early are usually easier to deal with.

If Halloween leaves you curious about wearing contacts every day, learn the daily routine properly first: rubbing and rinsing the lenses, replacing the case, keeping water away. The column on everyday contact lens care goes through it step by step, and regular checkups are part of the deal.

Some people wear colored lenses only once a year, for Halloween. Have your eyes checked each time anyway, because eyes can change in a year. Look at the expiry date on any leftover packs and throw out anything past it, and don't keep an opened lens for next time.

Changing your eye color is the part of a costume that sits closest to your eyes. The costume comes off at the end of the night; your eyes have to last the rest of your life. Get a proper fitting, wear the lenses the way you were told, take them out the moment something feels wrong, and then enjoy the night.