RGP LENSES

An RGP Lens with a Soft Lens Fit

By Chrysa Croatt, NCLC, and Edward Wing, FCLSA
June 2000

Practitioners who shy away from RGP lenses because they are more complicated to fit may have a solution.

Millions of people enjoy the advantages of wearing RGP contact lenses on a daily basis. These advantages, which include excellent optics, easy care and handling and superb health benefits, play a significant role in overall success. However, RGP lens use remains limited among contact lens wearers and fitters.

Practitioners may resist the idea of fitting their patients in rigid oxygen permeable lenses due to the perception that the lenses are too complicated to fit. While practitioners who are comfortable with RGP lenses have overcome the initial learning curve, others may not feel the end result is worth the effort. But what if patients could enjoy the benefits of a gas permeable lens while practitioners enjoy the ease of a soft lens fitting?

X-Cel Contacts hopes to incorporate the best of both worlds in its Visions lens. Visions combines the most successful aspects of X-Cel's current lens designs into one contact lens. It is a thin, back surface aspheric lens with a controlled edge lift. Each of those features alone would result in a more comfortable lens. We believe combining them in one design produces a comfort-enhanced contact lens that promotes patient satisfaction and success for even the first-time RGP lens fitter.

Park Nicollet Clinic, Minneapolis, evaluated the ease of fitting, patient comfort and overall success of the Visions lens design. Park Nicollet has no proprietary interest in the lens design, and had not utilized the services of X-Cel Contacts prior to this study.

Patient Demographics

Park Nicollet evaluated the Visions lens on a group of 40 patients (79 eyes total). The study included 25 females and 15 males, ranging from 11 to 62 years of age. The greatest representation of the candidates (35 percent) fell within the 11- to 18-year-old group. Some 48 percent of the patients had never before worn contact lenses (Figure 1).

The patients' corneas demonstrated a flat K range from 39.50D to 47.62D, with the largest number of eyes (38 percent) exhibiting a flat K between 43.00D to 43.87D (Figure 2). The amount of corneal cylinder ranged from 1.00D of against-the-rule cylinder to 3.37D of with-the-rule cylinder. The mode fell between 0.12D and 0.50D of with-the-rule corneal cylinder (29 percent) (Figure 3).

Figure 2.

Figure 3.

Patient Fitting

This study enrolled all appropriate RGP lens candidates without prejudice, placing no restrictions on potential candidates in an effort to look for the ideal patient. We included those patients whose corneal cylinder might make them more appropriate candidates for posterior toric lens designs. We used the nomogram provided by X-Cel to fit all of the patients in an effort to evaluate the effectiveness of a standard set of fitting guidelines. Patients received a routine evaluation at each follow-up visit, and lenses were reordered for the patients if we determined that vision, fit or comfort could be improved with a change in the lens design or power. At each follow-up visit, patients rated their comfort, vision and overall satisfaction.

Results

Overall, we successfully fit 70 percent of the patients with the Visions lens design. One focus of the study was to determine the ease of fitting the lens based on X-Cel's nomogram system. Some 17 of the 40 patients (42 percent) were successfully fit with the first pair of lenses by simply following the guidelines established by X-Cel. An additional 8 percent required a change only in the power of the lenses in order to succeed, which does not reflect the effectiveness of the nomogram. The 20 percent of patients who required a change in the fit underwent only minor changes in order to gain success.

Patients rated their comfort, vision and overall satisfaction at the two-week and five-week visits. At the two-week visit, using a scale from one to five with five representing "most satisfied," 73 percent of the patients rated comfort four or higher, 77 percent rated vision four or higher and 85 percent rated overall satisfaction four or higher.

After five weeks, 94 percent of the patients rated comfort a five, while 83 percent rated vision and overall satisfaction a five. All 100 percent of the patients rated comfort, vision and overall satisfaction at four or higher at their five-week visit.

The Ideal Candidate

When evaluating the results of the study more thoroughly, we found an "ideal" range of corneal cylinders. While every RGP candidate was enrolled in the study regardless of the amount or location of the corneal cylinder, those patients whose corneal cylinder was between 0.50D of against-the-rule and 2.00D of with-the-rule cylinder (by many standards, the ideal spherical RGP lens candidates), had a greater measure of success.

When evaluating those more challenging patients whose cylinder was outside of the "ideal" range, only 56 percent of those patients had success with the Visions lens, compared to a success rate of 80 percent for those patients whose corneal cylinder fell between 0.50D of against-the-rule and 2.00D of with-the-rule (Figure 4). The difference between these two groups may be attributed to the thin design of the Visions lens. Traditionally, thin contact lens designs perform less optimally with increased amounts of corneal cylinder due to flexure, and result in decreased vision and comfort.

In evaluating only the "ideal" group of corneal cylinder patients, we found that 50 percent were successfully fit with the first pair of Visions lenses even though no diagnostic lenses were used. Only 23 percent of the patients required a change in the fit, and none of the patients required more than one lens change in order to achieve success.

The breakdown of lens wearing history also provided interesting statistics regarding potentially successful populations of the Visions lens design. In evaluating the 12 patients that discontinued use of the Visions lens, we found that seven had previously discontinued soft lens use, two had previously tried RGP lenses and one tried Visions lenses after wearing PMMA lenses several years ago. Only two of the 12 patients who discontinued had never before worn contact lenses. Those patients who previously tried and failed with contact lenses are among the most difficult patients to successfully fit with lenses, making those results not surprising.

A closer look at those patients who had no previous lens wearing history revealed some encouraging results. Of those patients, 90 percent were successfully fit with the Visions lens. This was the largest population enrolled in the study, and the most successful. Among this group, the only patients that discontinued were those that fell outside of the "ideal" corneal cylinder range previously discussed. In other words, every new contact lens wearer in the ideal cylinder range was successfully fit with these lenses.

The Visions Lens

Eyecare professionals recognize the benefits of gas permeable contact lenses, and yet the market share continues to remain static. One possible reason for the lack of support among lens fitters may be the perception that rigid gas permeable lenses are difficult or complicated to fit. The myriad of parameters that comprise an oxygen permeable rigid lens can overwhelm even the most experienced soft lens fitters.

Visions by X-Cel has effectively removed these barriers by creating a gas permeable lens that is easy to fit. By simply supplying patients' K readings and refraction, or following the simple nomogram provided, practitioners can determine the lens parameters as quickly as soft lens parameters. There is no need to determine the peripheral curve system, optic zone diameter, edge design or center thickness because these parameters are controlled by the lens design. Contact lens practitioners need to determine only the base curve, diameter and lens power.

Visions blends the best of RGP and soft lenses, allowing practitioners to provide patients with the ultimate in vision, comfort, health and convenience. Each lens is packed in a vial and delivered fully hydrated to the patient, which increases initial comfort and wettability. The lens package includes an identical lens. Every patient can benefit by having a spare pair. This would include young or active patients, frequent travelers and those who are traditionally aggressive with lens handling.

The comfort that the patient enjoys while wearing the Visions lens accentuates the ease of fitting for the practitioner. Now practitioners can provide to patients RGP lens benefits with soft lens simplicity.