Contact Lens Design & Materials
Helpful Markings on Soft Torics
By Neil Pence, OD, FAAO
All soft astigmatism-correcting contact lenses have markings to identify the lens orientation. Did you know that some of these lenses also feature other useful markings?
Air Optix for Astigmatism
Air Optix for Astigmatism (Alcon) lenses have markings in the 11 o'clock to the 1 o'clock area of the lens. For example, a –3.00 –1.25 x 180 lens features the code CIBAB753. “CIBA” identifies the lens manufacturer (now Alcon). The “B” signifies the Air Optix for Astigmatism design. The number “7” represents a base curve of 8.7mm, and the “53” pertains to the mold used to create the sphere power. We often use the phrase “53 is –3.00,” and although the company indicates that this may not always be true, it is accurate most of the time.
For numbers other than 53, each number up or down represents 0.25D. For example, a “49” is four steps down, so the sphere power would be –2.00D.
PureVision 2 for Astigmatism
In PureVision 2 for Astigmatism (Bausch + Lomb), next to the orientation mark at 6 o'clock is a letter. On the upper half of the lens next to a smaller line is a second letter. Using the Lens Power Identification Chart (Table 1), you can determine lens power.
Using the same example, you would see an “M” to the right of the 6 o'clock line, which from the chart indicates a possible sphere power of –2.25D to –3.00D. Next to the smaller line would be a “B,” which is in the –1.25DC line in the cylinder power portion at the top of the chart. Dropping down from the “B” box until it intersects the “M” line identifies the sphere power as –3.00D.
Finally, the location of the smaller mark identifies the axis—at 180 degrees in our example.
Keep a Record
It is helpful to record identifying markings on contact lenses. They can help you quickly determine whether a lens on-eye is correct, saving time on future visits. CLS
|Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana. He is a consultant or advisor to B&L, Ciba Vision, and Vistakon, and has received research funding from AMO. You can reach him at email@example.com.|