Improve Visual Performance with an Aspheric Multifocal

Scott Schatz, OD, PhD, FAAO
August 2000

The Essential RGP series incorporates the best performance characteris-tics of simultaneous and translating designs.

There are approximately 80 million presbyopes in the United States today, and that number is increasing at a rate of five million people per year. While the number of patients wearing multifocal contact lenses is increasing at a rapid rate, the total multifocal population is only one percent of the contact lens market. As the need for near vision correction is increasing, a larger segment of this population will consider using bifocal or multifocal contact lenses.

The two basic types of bifocal contact lens designs are alternating vision, similar to a spectacle lens bifocal, and simultaneous vision, in which both distance and near fields of vision are focused on the retina, and the patient chooses which field to observe. A modification of the spherical simultaneous bifocal lens into an aspheric lens allowed for the introduction of a multifocal or progressive- addition contact lens. No early bifocal lenses that have been prescribed have achieved a high level (>50 percent) of patient satisfaction.

In the past two years, several new bifocal contact lenses have been introduced. We conducted a study that examined the efficacy of the Essential aspheric multifocal lens, a rigid gas permeable bifocal contact lens manufactured by Blanchard Contact Lens Incorporated.

Lens Design

Each of the Essential RGP lens series are fit in the same fashion consistent with a corneal alignment fitting philosophy. When more add is needed, the next successive series provides greater add while retaining base curve, diameter and distance power specifications from the prior lesser series.

The simplified fitting process available with the Essential RGP lens is a result of the posterior power gradient created with proprietary S Form technology. Each series has successively greater amounts of add correction contained within a 4.0mm radius of the center of the posterior surface. Optics created within this radius fall within a usable optical area anterior to the pupil. Essential lenses are translating aspheric multifocal lenses by design, seeming to contain more effective add than conventional CNC-produced aspheric lenses.

Patient Selection

Prior to enrollment into the study, all patients were required to have a complete primary care examination. Patients had to be free of any ocular pathology that would prevent them from being a good contact lens candidate.

Some 44 patients were enrolled into the study. Prior vision correction modalities included patients who were new to contact lens wear and current or previous wearers of hydrogel or RGP lenses. Modalities of correction included progressive or bifocal spectacles (14 patients), single vision RGP lenses with reading glasses (10 patients), and monovision RGP and hydrogel contact lenses (7 patients). Seven patients were emerging presbyopes currently wearing single vision spectacles or contact lenses, two were emerging presbyopic patients not wearing corrective lenses of any type, while four patients were wearing another type of bifocal or multifocal RGP lenses. Our study population was representative of the presbyopic population in general, with only nine percent wearing bifocal/multifocal RGP lenses.

Evaluation of the contact lens fit included the following: centration in primary and up gaze, lens movement in primary and up gaze, visual acuity (distance and near), stereoacuity, contrast sensitivity (distance and near), trial frame over refraction (distance and near) and binocular subjective range and biomicroscopic analysis of the cornea. The patients were required to wear the lenses on a daily wear basis and clean the lenses in the evening with an appropriate cleaning regimen as prescribed by the manufacturer. Lens care systems utilized during the study included Boston Original conditioning and cleaning solutions, Boston Advance Comfort Formula conditioning and cleaning solutions and Boston Rewetting drops. The same evaluation procedures were carried out during each follow-up evaluation at one week, three weeks and four weeks and included corneal topography of the corneal surface. Each patient completed a series of post-study questionnaires regarding the available options for distance and near vision correction and their subjective preferences (Figure 1).

Figure 1. The majority of study subjects reported superior visual performance and comfort compared to their pre-study modality of correction.

Patient Results

The Essential RGP lenses displayed considerable versatility of fit and application throughout a wide spectrum of the presbyopic patient population (Table 1). Essential RGP lenses provided very good distance, intermediate and near vision with improvements in night vision and overall comfort. Of the 44 patients entering the study, 43 completed the study, with a majority reporting visual performance and comfort superior to their pre-study modality of correction.

TABLE 1: Clinical Profile of Study Patients: N=44  

Questions in the Essential RGP post-study questionnaire were designed to be specific to the general visual requirements of the study population. These included overall visual performance, distance vision, near vision, intermediate vision, night vision and patient comfort. Patients provided a subjective numerical grade ranking visual performance of the study lenses. The study group reported marked improvement in all visual performance categories particularly in near, intermediate and night vision, with the most significant improvement occurring in near vision. It is worth noting the improvement in visual performance in one category was not at the expense of other aspects of visual performance or patient comfort.

Individual patient responses regarding visual performance relative to specific distance refraction, add correction and prior modality of correction were evaluated. A majority of the patients reported marked improvement across all categories of visual performance. Responses were categorized as 10, 5 and 0, with 0 indicating "dissatisfied," 5 indicating "somewhat satisfied" and 10 indicating "very satisfied."

Overall satisfaction. Some 84 percent of the study group reported their overall level of satisfaction as "very satisfied" when compared with their prior modality of vision correction. Some patients who might be perceived as difficult to fit such as emmetropic, astigmatic and emerging presbyopes were quite successful in this study. Our study population included three patients with refractive errors less than 1.00D with add corrections of +1.00D, +1.50D and +2.50D. Two of those patients scored consistently "very satisfied." Those patients who were "somewhat satisfied" included three high myopes wearing bifocal or progressive spectacles.

Distance vision. Distance vision performance represented the lowest margin of improved visual performance. Most patients were already corrected for distance viewing and should not perceive an improvement but may appreciate continued clear distance vision. Of the 16 patients scored as "dissatisfied" for distance performance, 10 were previously wearing single vision RGP lenses, four were previously wearing progressive spectacles and two were previously wearing bifocal contact lenses.

Their less than satisfactory vision may have been due to the inherent difficulties in correcting multiple focal points while maintaining the clarity and crisp quality of distance vision with single vision contact lenses or spectacle correction. The optics of single vision RGP contact lens correction and spectacles will, in general, outperform other types of vision corrective design. Interestingly, five of the six patients who reported being "dissatisfied" for distance visual performance reported being "very satisfied" with the overall performance of the lenses. This indicates that a significant proportion of the population may be willing to sacrifice a bit of specific visual clarity for a more global feeling of visual comfort.

Near vision. Near vision performance provided the greatest margin of improvement among the study population. Some 91 percent of our study population, representing a broad range of near vision requirements, reported being very satisfied with their near vision performance.

Intermediate vision. In intermediate visual performance, 86 percent of the patients reported being "very satisfied." Tasks requiring good intermediate performance were easily accomplished. The aspheric optics available with Essential RGP lenses provided a continuous range of focal point correction from near through intermediate to distance. S Form lathing provides a continuous graded aspheric optic absent of transition points created with CNC lathing. These areas of transition from one sphere power to the next are nonoptical and serve to degrade overall quality of vision.

Night vision. Patients were very satisfied with the nighttime visual performance obtained with the Essential RGP. Very few patients complained of vision reduction due to glare or halo. Patients can experience nighttime visual performance problems when wearing multifocal lenses. Common complaints are a reduction in visual acuity, a loss of visual contrast and excess glare and haloes. We believe more distance optical area is available in dim illumination than with CNC produced lenses.

Comfort. In general, patients reported higher levels of comfort with the Essential RGP when compared to their experience with other contact lenses. The scoring for overall comparison of comfort to lenses worn prior to the study was not surprising because the aspheric posterior surface present with Essential lenses is designed to enhance comfort. Absence of peripheral and intermediate fitting curves and the accompanying blends and junctions leads to initial and long-term comfort. Several patients who reported as "somewhat satisfied" continued to wear their lenses after the study was completed.

The role of patient expectation and motivation in ensuring success with bifocal lenses cannot be overemphasized. While a number of patients found a problem with an aspect of visual performance of the lenses, their evaluation of overall visual performance was high.

Essential RGP lenses provided good distance and intermediate vision, as well as exceptional near visual performance for a variety of working distances, incorporating the best performance characteristics of simultaneous and translating lens designs. In addition, we noticed an absence of patient complaints regarding glare and/or halo at night. The broad range of corrections utilized in this study demonstrates the superior capabilities that the Essential RGP lens design offers contact lens practitioners and their presbyopic patients.

The author wishes to acknowledge the following practitioners for their assistance with the study: Lisa Badowski, OD, MS, FAAO; Susan Gromacki, OD, MS, FAAO; Hadley Saitowitz, OD; Donna Wicker, OD, FAAO; and Mark Ventocilla, OD, FAAO.

Dr. Schatz is professor of optometry and chair of the Basic Sciences Department at Nova Southeastern University College of Optometry. He is also adjunct professor of oceanography at the NSU School of Oceanography.