Reader and Industry Forum

Don't Flip Over Lens Inversion Markers

By Etty Bitton, OD, MSc, FAAO, & Lyndon Jones, FCOPTOM, PhD, FAAO

Prior to soft lens application, the correct orientation of the lens must be confirmed. In the early years of soft lens designs, particularly when lenses were relatively thick, patients were simply instructed to place the lens on the tip of their index or middle finger to assess the profile of the lens edge (Figure 1). A lens that was facing the correct way would have the appearance of a “bowl,” while the edges of an everted or inverted lens had a tendency to turn outwards slightly, resembling a “dish.” If patients were uncertain, they could “pinch” the lens slightly (Figure 2). If the lens edge tended to turn inward, then the lens was facing the correct way, and if the edges turned out toward the fingers, then the lens was everted.

Figure 1. Visualizing the lens edge on a finger.

Figure 2. “Squeezing” the lens to determine its orientation.

However, with the passage of time and improved lens designs that are focused on enhancing comfort, it has become far more difficult to assess whether a lens is inverted or not.

Inversion Markers

To overcome this, a number of contact lens companies have used “inversion indicators” or “inversion markers” on soft lenses as a way to assist patients and practitioners in determining when a lens is everted. The inversion markers typically consist of the name (or variation) of the company selling the lens or are a series of letters or numbers, which will read appropriately when the lens is facing the correct way. The marker helps to ensure that the lens has been applied the correct way.

Additionally, when the lens is on the eye, the inversion indicator allows practitioners to verify that the concave side is oriented toward the corneal surface.

With the advent of multifocal soft lenses, these markers are becoming more valuable in helping presbyopes correctly place the lens on their finger prior to application. Table 1 summarizes some of the inversion markers available on modern soft lenses.

Don't Let This One Confuse You

Among the contact lenses using such inversion markers is the Air Optix Night & Day Aqua (Ciba Vision [Ciba]) contact lens, lotrafilcon A, which is available in sphere powers only. This lens uses an “OK” inversion indicator with a height of nearly 1.7mm, which is very easy to visualize (Figure 3). However, one point to remember is that because the contact lens can rotate 360 degrees on the eye, the “OK” indicator can take on different appearances to clinicians (Figure 4). Patients should place the lens on their finger so that the “OK” is on the outside (i.e., the convex side) of the lens. When the contact lens is applied, the “OK” indicator reads as “OK” only when it is at the 12 o'clock position.

Figure 3. Size comparison of the inversion markers for (left) the new 1-Day Acuvue TruEye (slightly more than 2mm) and (right) Air Optix Night & Day Aqua (1.7mm) lenses.

Figure 4. Appearance of the “OK” inversion marker of the Air Optix Night & Day Aqua when properly positioned and when the lens is everted.

Properly applied, if the contact lens rotates and the marking is at 6 o'clock, it will read “

O.” If the lens is inverted upon application, then the inversion marker will read “OK” at 6 o'clock. This has led to some confusion among practitioners thinking that an “OK” at 6 o'clock is a correct fit when in fact the lens is everted. Educating personnel and patients as to the proper positioning of the contact lens on the finger will ensure that the lens is properly oriented on the eye every time.

Helpful for Presbyopes

The emerging presbyopes of the baby boomer generation will likely drive more multifocal contact lens options in the market. Inversion indicators will be extremely valuable to ensure proper application of these lenses and to maintain good vision and comfortable contact lens wear. CLS

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Dr. Bitton is an associate professor of optometry at the École d' optométrie, Université de Montréal and is the Externship Director. She is also the current chair of the Association of Optometric Contact Lens Educators (AOCLE). She is a consultant or advisor to Ciba Vision. Dr. Jones is director of the Centre for Contact Lens Research and a professor at the School of Optometry at the University of Waterloo. He has received research funding from Alcon, AMO, B+L, Ciba Vision, CooperVision, Johnson & Johnson, and Menicon.