Contact Lens Practice Pearls
A Case For Custom Soft Lenses
By John Mark Jackson, OD, MS, FAAO
Custom soft lenses have gained a lot of traction in the last few years. Many of our “stock” lenses now come in only one base curve and diameter. While these lenses fit well on the “average” cornea, by definition we will have patients who don't fit the mold. Custom soft lenses can help us fit these corneas that stray from the norm.
No Luck With Stock Lenses
Our patient was in his 20s and had been wearing soft lenses for more than 10 years. He stated that a “perfect” fit had never been achieved. Although he had adapted to his lenses, every brand he had tried resulted in excessive movement and poor corneal coverage. Figure 1 shows his current lens, an Acuvue Advance (Vistakon) lens with an 8.3mm base curve and 14.0mm diameter.
Figure 1. Habitual stock soft lens with excessive lag.
Note the huge amount of lag visible in upgaze! When the patient looked straight ahead, it was easy to see that the lens edge was closer to his limbus than you would normally see. I was surprised that he had been able to adapt to lens wear with a fit this poor. We tried other stock brands in a 14.2mm diameter with the same results.
Custom Lenses to the Rescue
We measured his corneal diameter with the topographer (Figure 2). While a typical cornea is about 12mm, his corneal diameter was 12.5mm. This may not seem like much of a difference, but the larger diameter means he also has a deeper-than-normal sag depth and therefore needs a lens with a deeper sag, too. Note that his flat K value is 41.75D, which would usually lead you to a flatter soft lens. But this combination of curvature and large diameter results in a deep corneal sag and a loose-fitting lens.
Figure 2. Topography showing large corneal diameter.
We ordered a custom soft lens (Flexlens from X-Cel Contacts). Our best fit was with an 8.3mm base curve/14.5mm diameter combination. We chose the 14.5mm diameter to provide 1mm of extension beyond the limbus. Note that we ended up with a lens with the same base curve, but with a larger diameter than that of a typical stock lens. Figure 3 shows how this lens still centers nicely in upgaze. In primary gaze, it demonstrated good movement and corneal coverage.
Figure 3. Good lens lag with larger custom soft lens.
The patient experienced better comfort with this contact lens and was pleased with the improvement in fit.
Many GP labs now also make custom soft lenses. If you haven't used custom lenses, talk to your lab about your options and obtain a few trial lenses in a range of diameters. Your lab can guide you on how to select the correct parameters for each case.
Worth the Effort
Custom soft contact lenses can make your practice stand out and create loyal patients in the process. When patients understand that you are making an extra effort to take care of their eyes, they will appreciate that they're in good hands. CLS
|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 firstname.lastname@example.org.|