Three Tips for Corneal GPs
BY CATHERINE TUONG, OD, & JOHN MARK JACKSON, OD, MS, FAAO
In an increasingly competitive contact lens market, GP lenses are a great way to provide a premium option to patients, build patient loyalty, and, in turn, grow a practice. Following are three easy tips that can be utilized in GP fitting.
Tip #1: Flexure
It’s easy to forget that corneal GPs are actually somewhat flexible. Flexure occurs when a lens bends while it is on the eye. It is more likely to occur with higher corneal cylinder, a steep fitting relationship, larger diameters, and higher-Dk materials.
Suspect flexure when patients complain of fluctuating visual acuity with blinking. Check for flexure by performing keratometry over the lens; a spherical lens that is flexing will show a small amount of toricity on the front of the lens.
The optical effect of flexure is that the tear film power will change under a flexing lens, decreasing the amount of cylinder correction in the tears.
This may not be a bad thing in all cases. For example, if a patient’s corneal cylinder is greater than the refractive cylinder, the reduced tear film cylinder might provide better correction.
Most of the time, though, the fluctuating correction is a problem. To fix flexure, you can flatten the lens, increase the center thickness, or try a lower-Dk material.
Tip #2: Choose the Right Base Curve Design
Getting the best alignment relationship with a GP lens is easy if you pick the right design. Corneas that have less than 2.00D of toricity can usually be fit with a spherical base curve. Higher than 3.00DC will likely require a bitoric or back-surface toric design.
If you are between 2.00DC and 3.00DC, try a sphere or aspheric design and assess the fit. If it’s unstable or shows an uneven alignment, switch to the toric design.
The corneal topography may also dictate which design to use; a cornea that has limbus-to-limbus astigmatism is more likely to need a toric lens compared to a central-astigmatism cornea (Figure 1). It is important to remember that toric corneas also contribute to flexure, and a toric design can minimize this as well.
Figure 1. Limbus-to-limbus astigmatism (left) is more likely to need a toric base curve compared to central astigmatism (right).
Tip #3: Use an Anesthetic
Initial lens comfort is a key to a successful fitting process. Using a drop of proparacaine can make the experience much easier for both patient and practitioner. A new GP wearer will have reflex tearing and increased lid tension, which make it difficult to assess the lens fit and make the patient less comfortable.
Some practitioners feel that this gives the patient a false impression of how the lenses will feel. However, the anesthetic wears off quickly enough for the patient to have a better initial experience, but a realistic impression as well.
GP lenses offer many benefits to patients. We hope that these few tips will aid in your fittings and help grow your practice. CLS
Dr. Tuong is the current Cornea and Contact Lens 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.