Empirical Fitting With a Toric Soft Lens

BY KARL ENGLEHART, O.D., THOMAS FINLEY, O.D., JONATHAN GELLER, O.D.,BARRY T. KISSACK, O.D., MARIE KITKO, O.D.,MARTIN MCDOWELL, O.D., RONALD SEGER, O.D., JOSEPH STUDEBAKER, O.D., & SHARON D. TEAGUE
DEC. 1996

This multisite study assessed whether empirical fitting using a predictable toric lens could render trial fitting superfluous.

Many practitioners are accustomed to fitting toric lenses empirically only out of necessity -- when the patient's prescription is such that no reasonable trial lens is available. In this study, we evaluated the Preference Toric lens from CooperVision, a daily wear, prism-ballasted, back-surface toric soft lens, to determine if this design is stable enough to allow empirical fitting in all cases, not just the exceptional ones.

The main purpose of trial fitting a toric lens is to determine the amount of rotation in order to incorporate compensation in the prescription lens. The combination of a spherical fitting curve, a toric optic zone and an eccentric lenticular zone make the Preference Toric lens quite stable, and since it rarely rotates more than five degrees, it's also predictable to fit.

PROCEDURE

We recruited 68 astigmatic patients, the majority of whom were satisfied wearers of other types of contact lenses. All participants had a desire to wear contact lenses, were willing to participate in a three-month study, had a prescription within the range of parameters offered and had no ocular pathology. Table 1 summarizes patient demographics. After an initial examination, we selected a base curve based on keratometry readings and determined power from the vertex-corrected spectacle prescription.

We dispensed Preference Toric lenses and a multipurpose chemical disinfection system without enzymatic cleaner to the patients. We determined fitting characteristics via biomicroscopy, recorded visual data using standard clinical procedure, and questioned the patients on comfort. We reinstructed all wearers in lens care procedures.

There were four scheduled follow-up examinations during the three-month study. Patients answered a detailed subjective questionnaire at all visits, describing their satisfaction with the new lens design and relating their experience with the new fitting modality. At the conclusion of the study, we also completed a questionnaire detailing our satisfaction with the lens and the fitting process.

RESULTS

We measured clinical success along four criteria: comfort, physiology, visual acuity, and reliable and efficient fitting characteristics.

Comfort: Patients rated the comfort of their new lenses on a scale of zero to five, with zero signifying a painful lens and five indicating excellent comfort. The mean comfort level was 4.11 at the dispensing and 4.12 after three months of wear, indicating a successful patient comfort response.

Physiology: There were no adverse physiological reactions reported during the study. At the one-month visit, eight eyes (7%) exhibited trace corneal staining and 27 eyes (24%) reported mild to trace injection. At the three-month visit, all findings were minimal trace findings which are clinically acceptable in the normal patient population.

Visual Acuity: Using the empirical fitting method, 93 percent of eyes were corrected to acceptable acuity with the first lens dispensed. At the three-month visit, 90 percent of eyes were corrected to 20/20 or better, and the remaining were deemed to be clinically acceptable (Fig. 1). At each visit, patients also rated their visual acuity on a scale of one to five, with five being the best. The mean acuity rating ranged from 4.04 at dispensing to 4.2 at the three-month visit.

Fitting Characteristics: For a toric soft lens fitting to be successful, the lens must position and move well on the eye with minimal rotation, and any rotation must be stable. In our study, we judged the fitting relationship using a standard slit lamp biomicroscope.

At dispensing, 92 percent of the empirically fitted lenses were deemed to fit optimally, and the other 8 percent were marginally acceptable. By the one-month visit, 98 percent of the lenses were considered well-fitting, and at the three-month visit, all lenses were considered acceptable. Rotation with the Preference Toric was minimal, and this accounts in large part for the success of the study fittings in terms of visual acuity and fitting characteristics (Fig. 2).

The average number of lenses used per eye was 1.25 (+0.40) with a range of one lens to three. Of the 128 eyes completing the study, 94 (73%) were wearing the first lens dispensed and 34 (27%) were wearing the second lens. There were no torn lenses during the course of the study.

DISCUSSION

While fit, vision, comfort and physiology are merely indicators, the true measure of success is patient and practitioner satisfaction. Subjective visual quality is an important real-world consideration, particularly when assessing visual acuity. After all, who hasn't had a patient who complains of blurry vision through his new lenses when objectively, he is corrected to 20/20 or better?

Therefore, at the conclusion of the study, we questioned patients in detail about their satisfaction with the Preference Toric lenses. Because the majority of them were already satisfied toric soft contact lens wearers, these patients had a strong basis for correlation of the new lenses with the norm, and may have had higher expectations than patients receiving their first correction. As shown in Figure 3, patients were generally very pleased with the quality of vision provided by Preference Toric lenses.

Patients also rated the lenses as easy to handle; the mean response was 8.5 on a scale of one to 10. About half of the patients rated their Preference Toric lenses as excellent overall, and another 36 percent were pleased with the new lenses (Fig. 4).

CONCLUSION

This study showed that when paired with a reliable toric lens such as the Preference Toric, empirical fitting saves chair time without sacrificing patient satisfaction.

The next time you're faced with a tough astigmatic patient, no time and a pressing need to succeed, fit empirically. It will work as well for you as it does for us. CLS

The authors wish to acknowledge the assistance of Dr. Joseph T. Barr in this study.

This study was sponsored by CooperVision, Inc.