Markings on Contact Lenses

When you wear contacts, your vision becomes a purplish-colored filter that can be used for reading luminous “invisible markings”. The markings on contact lenses can appear as a circle-shaped number or a series dots. When viewed under a light source, these markings will glow. They can tell if your lenses are inside out.

Contact lenses that are flipped inside out will not fit correctly on your eye’s curvature and can cause blurred vision. The wrong-way lenses can also feel uncomfortable and like they are lightly scrubbing your eyeball.

Reference markings are available on many soft contact lenses, as well as some GP and scleral lenses. These markings help the lens fitter to prevent the lens from rotating on the cornea. These markings can be in the form of circles or lines, and their size, position and shapes can vary. These markings are generally located at the 6 o’clock and 12 o’clock positions on the lens, with each number representing an angle location (like a dial). The fitter can determine the direction of rotation by comparing the lens position to the reference markings. This is also known as “Left Subtract, Right Add” or LARS.

Some contact lens manufacturers put laser markings on their lenses to make it easier to determine whether a contact lens is correctly oriented. These may be small numbers such as ‘123’ and can be found on both coloured and clear contact lenses. Place the lens on your finger, and hold it to a bright light. If the numbers appear reversed, then the lens will be inside out.