A Review of GP Lenticulation and Carriers
BY BRAYDEN LUNDQUIST, OD, & JOHN MARK JACKSON, OD, MS, FAAO
Lens edge profiles and mass play a key role in the lid-lens interaction with GP lenses. Lenticulation is used to achieve an ideal balance of edge thickness and lens mass to enhance the lens movement dynamics and comfort.
When does lenticulation need to be used for corneal lenses? Stein and Slatt (1984) explain that the wrong edge profile adversely affects lens performance in many ways, including improper lens positioning, development of 3 o’clock and 9 o’clock staining, dellen formation, and discomfort. Lenticulation alters the front surface to enhance the edge shape and lens mass.
Benefits of Lenticulation
In Figure 1, the blue line shows the front surface of a plus lens before lenticulation. The lens has a thick center (excess mass) and a very thin edge (poor lid attachment). The red line shows the front surface after lenticulation. The edge is now nearly parallel with the back surface, helping lid attachment. In addition, the lens has less mass (decreasing lens drop) as well as better Dk/t.
Figure 1. Lenticulation profile of a plus lens.
This particular shape is called a “plano carrier” due to the parallel surfaces in the periphery. A “minus carrier” is similar, but has a thicker edge that mimics the edge shape of a moderate-power minus lens to provide more lid attachment, if needed. Also, note that low-minus lenses actually have relatively thin edges and can benefit from a plano or a minus carrier as well (Bennett and Henry, 2014).
In Figure 2, the blue line shows that a high-minus lens has very thick edges before lenticulation. The thick edges cause discomfort and excessive lid attachment. The red lines show the front surface after lenticulation. The edge is thinned to create a more ideal shape. This shape is called a plus carrier because it decreases edge thickness. Plus lenticulation is typically used in powers greater than –5.00D (Mandell, 1988).
Figure 2. Lenticulation profile of a high-minus lens.
Do you always need to tell the GP lab to lenticulate a lens? Bob Martin (2016) from Blanchard Contact Lenses explains that today’s computer-controlled lathes make edge thickness and center thickness issues less of a worry than in the past. Most labs target specific center and edge thicknesses, so all powers are generally lenticulated to some degree to create optimal lens shapes. However, it is best to discuss this with your lab consultants to ensure that you know their procedures.
Know Your Options
When corneal lenses don’t position where you want, there are several options to consider, including the lens diameter and the alignment relationship. But, the edge profile plays a critical role as well. Consider the lens power and how that can affect the edge shape, and discuss adding or modifying lenticulation with your lab. These changes can be particularly helpful in patients who are adapted to a particular diameter or base curve. CLS
For references, please visit www.clspectrum.com/references and click on document #246.
Dr. Lundquist is the current cornea, contact lens, refractive surgery resident at Southern College of Optometry. Dr. Jackson is an associate professor at Southern College of Optometry where he works in the Advanced Contact Lens Service, teaches courses in contact lenses, and performs clinical research. You can reach him at email@example.com.