How Can You Tell a Lens Is Inside Out?
You put your lens on this morning and something feels off.
It doesn't hurt, but it keeps nagging at you, and every time you blink the lens feels as if it is floating. One of the first things to suspect is that the lens may be inside out.
A soft lens is thin and flexible, and it changes shape easily on your fingertip. So telling front from back is quite hard at first.
The basic check is the shape, before it goes on your eye
The American Academy of Ophthalmology advises this check before you insert a lens. If the lens forms a bowl and the edges turn up, it is ready to go on the eye. If it looks like a lid, with the edges turning outward, it needs to be reversed.
A lens is made to sit on the round surface of the eye, so the right way round it forms a rounded, cupped bowl, and inside out its edges flare open.
The same guidance adds that you should wash your hands before handling a lens, but avoid soaps with oils or fragrance, because these can stick to the lens surface.
There are several ways to check
Manufacturers and eye care guidance describe four main methods.
- Shape check: look at the lens on your fingertip. Is it a bowl, or do the edges flare open?
- Gentle fold (the taco test): pinch the lens lightly between thumb and forefinger. If the edges come inward, it is known to be the right way round. Do not press hard.
- Marking check: some products have numbers, letters or a logo engraved near the edge. If they read correctly, the lens is the right way round; if they appear backwards, it is inside out.
- How it feels: an inverted lens may feel more like a foreign body, or less stable, than one that went on correctly.
Markings differ from product to product
Not every lens has markings. The type, position and way of reading them depend on the manufacturer and the product.
That is why this article does not generalise to "if you see this number, it is correct". The instructions for use inside the box are the most accurate guide to the markings on the lens you use.
Lenses where direction matters, such as toric lenses for astigmatism, sometimes carry separate markings that show their position. Some of these markings are not meant for checking inversion, so read the instructions for your product as well. Why a toric lens must not rotate is covered in Why a Lens for Astigmatism Must Never Spin on Your Eye.
If it feels uncomfortable after you put it on
Once on the eye, the lens should sit in place, feel comfortable and let you see clearly. If not, it may be inside out, or there may be another reason.
- If you suspect it is inside out, take the lens out, rinse it as the instructions for use say, check the shape again and put it back.
- If it is still uncomfortable, do not keep wearing it and put up with it. There may be a reason other than inversion.
- If you have pain, marked redness, light sensitivity or sudden blurring, do not put the lens back in, and have it checked by a professional.
The manufacturer's guidance page also links to a way of finding an eye care professional.
Good to know
- If you tore a daily lens while dropping or turning it, use a new one.
- Habits for putting lenses in and taking them out are also covered in The Dirtiest Thing Was Not the Lens. It Was the Case.
Telling front from back only feels strange for the first few days. Once you are used to it, it becomes a three-second habit before the lens goes on your eye.
References
- American Academy of Ophthalmology, How to Put In Contact Lenses
- ACUVUE, How to tell if your contact lenses are inside out
This article is general information. Follow the instructions for use and the advice of a professional for how to wear and care for your lenses. If you have pain, redness or a change in vision, stop wearing them and seek care.