Four Common Questions for GP Fitters
BY EDWARD S. BENNETT, OD, MSED, FAAO
In today’s GP practices—notably with new practitioners who have GP patients—certain common challenges are presented. I will address four in this column, concerning GP modification, material selection, corneal desiccation, and adaptation.
Should We Still Modify Today’s GP Lenses?
This is becoming more questionable with today’s materials and lens designs. Plasma-treated lenses should not be subjected to any front-surface modifications such as surface polishing and repowering. However, to established GP fitters, the ability to make small changes in the power (when possible) and back-surface periphery as well as edge polish can solve problems conveniently for patients. Edge polishing in particular is a simple procedure that can solve problems with little risk of impacting the quality of the lens (Bennett and Parker, 2013). For modification supplies, contact Larsen Equipment Design (http://larsenequipment.com/rgp-polishers/#).
What Material Should I Use?
My preference has been a low-Dk material (i.e., 25Dk to 50Dk) for daily wear myopic patients, a high-Dk material (i.e., 51Dk to 99Dk) for daily wear hyperopic patients, and a hyper-Dk (i.e., ≥100Dk) for all extended wear patients. That said, many of the designs manufactured by laboratories are often available in specific materials, removing this issue altogether. The laboratories are very aware of what material(s) would be most successful with a given design. It is important to use fluorosilicone acrylate lens materials rather than silicone acrylate—and not PMMA.
How Much of a Problem is 3 o’clock and 9 o’clock Staining?
Peripheral corneal desiccation, or 3 o’clock and 9 o’clock staining, has usually been reported as occurring in anywhere from 40 percent to 90 percent of GP lens wearers, with clinical significance in 10 percent to 15 percent (Henry et al, 1986; Solomon, 1986; Edrington and Barr, 2002). However, it is evident that the incidence is much lower. This is due to several reasons:
• Less inferior decentration is present. It has been found that inferior decentration results in approximately two times the incidence of corneal desiccation compared to a lid-attached fit (Henry et al, 1986). This occurs less often for several reasons, particularly new technologies including ultrathin lenses and lower edge lift peripheral designs.
• Today’s GP lens materials offer improved surface wettability due to plasma treatment, better affinity for mucin layer attraction, better scratch resistance, and other factors.
Can I Improve Patients’ Initial Comfort and Adaptation?
Sometimes we are more concerned about initial comfort than patients are, but it is an important consideration. Avoid terms such as “discomfort” and substitute “awareness.” I typically tell patients that GP lenses are smaller compared to soft lenses and move more on the eye, resulting in some awareness. However, this gradually goes away, and total comfort is typically achieved within a few weeks. The use of a topical anesthetic immediately prior to application is beneficial as well. However, the most significant recent breakthrough has been improved lens designs resulting from high quality lathes. The resulting ultrathin designs are complimented by increased larger-diameter lenses—including mini-sclerals on healthy eyes—that bode well for the future. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #216.
Dr. Bennett is assistant dean for Student Services and Alumni Relations at the University of Missouri-St. Louis College of Optometry and is executive director of the GP Lens Institute. You can reach him at email@example.com.