A Closer Look at Lens Comfort
BY EDWARD S. BENNETT, OD, MSED
Recognizing that initial comfort is the primary GP lens hurdle for both patients and practitioners, following are four reasons why it is evident that this challenge is less of an issue today.
1. Before the Fit How you present GP lenses can have a significant effect on initial comfort. Avoid the term “discomfort,” but use “lens awareness” and “GP” versus “rigid” to optimize the initial experience. Likewise, using a topical anesthetic immediately before the initial application will help patients through the first several minutes when they are most apprehensive. In fact, one study (Bennett et al, 1998) found that 38 of 40 patients who were given a topical anesthetic immediately before application successfully adapted to GP wear; only 32 of 40 who were not given an anesthetic successfully adapted.
2. Empirical Fitting The quality of GP lenses today makes empirical fitting a good choice for all but advanced specialty GP designs. With empirical fitting, the first GP lenses that patients wear will provide the primary benefit of GP lenses—very good vision. It would not be surprising if this reduces initial lens awareness. Every laboratory has a program, typically with a simple design nomogram, that makes empirical fitting easy and successful.
X-Cel Contacts Visions Ultra Thin lenses are such a design and can be ordered in a two-pack so that patients can always have a spare pair. In addition, the GP Lens Institute (GPLI) will soon be launching “Click N' Fit” on its Web site (www.gpli.info), which will allow simulated interactive GP lens fitting and evaluation.
3. Lens Design It is evident that larger-diameter lenses are more initially comfortable than smaller lenses are. Whereas an average GP diameter was once 9.00mm, it is now in the 9.50mm to 10.00mm range with intralimbal and mini scleral designs being much larger. With a normal upper lid-to-limbus relationship, a larger lens should provide a lid attachment fitting relationship in most cases. If the upper lid is at the superior limbus or above, a smaller diameter (9.00mm) with a resulting intrapalpebral fitting relationship is recommended.
The base curve radius is typically slightly flatter than flat K to better align with a progressively flattening cornea. Exceptions are patients who have moderate toricity or hyperopia in which a steeper-than-K lens may result in better centration.
An ultrathin design is recommended for patients who have ≤1.50D of corneal astigmatism to reduce lens mass and improve centration. Design the periphery so that edge clearance is slightly greater than central clearance. A peripheral radius no flatter than 11.00mm and no wider than 0.30mm should accomplish this goal, as would aspheric and pseudo-aspheric peripheries.
Excessive clearance (flat and wide peripheries) will result in greater upper lid awareness, possible compromise of the blink, funneling of the tears underneath the lens from the corneal periphery, and greater likelihood of corneal desiccation.
With these designs and improvements in lens materials and surface properties, we could argue that corneal desiccation has a lower incidence compared to 20 years ago. Likewise, GP edge quality is more consistent, almost eliminating the need to modify current designs, although having the ability to modify will always ensure that a problem can be immediately solved.
4. Resources. Your most effective resource is your laboratory consultants. These individuals are critical to patient success. In addition, the GPLI has numerous resources on its site to assist in fitting and problem-solving.
The bottom line: established GP practitioners do not have a problem with comfort. Once experience is gained with GP lenses, patient satisfaction, practitioner enthusiasm, and practice growth are the common outcomes. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #171.
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and is executive director of the GP Lens Institute.