Article Date: 12/1/2001

RGP MULTIFOCAL

A Clinical Study Of an RGP Multifocal Contact Lens

By Susan J. Gromacki, OD, MS, FAAO, Lisa Badowski, OD, MS, FAAO,
Donna Wicker, OD, FAAO, and Mark Ventocilla, OD, FAAO
December 2001

This study compares the acuity of an RGP multifocal contact lens to the acuity of spectacles in presbyopic patients.

As the "baby boomer" generation ages, there has been a substantial increase in the numbers of new presbyopic patients. The current presbyopic market in the United States is about 89 million people. This number is projected to grow at an annual rate of 4 percent to nearly 100 million people. Many of these patients are successful single-vision contact lens wearers who wish to continue as such. Others are emmetropes who have not previously worn any correction and are not motivated to start wearing spectacles to correct their presbyopia. This new presbyopic patient population, therefore, has the potential for great growth over the next several years.

The contact lens bifocal/multifocal market, however, has been severely limited by many factors, some of which include: inadequate vision at either distance or near, increased chair time required to fit lenses, limited lens designs, expensive products, poor reproducibility of lenses, decreased tear quality, decreased ocular media transparency and an overall perception that the lenses just "don't work." As a result, many current lens wearers become contact lens dropouts, and potential new candidates are not actively recruited. Only 8 percent to 10 percent of the entire contact lens market consists of multifocal/bifocal fits. The contact lens industry has tried to respond to this increasing need for better bifocal/multifocal designs by trying to improve lens designs and producing lenses that are simpler to fit and provide improved vision at all distances.

Rigid gas permeable (RGP) bifocal/multifocal lens designs achieve their bifocal power effect by using either translating (alternating) vision optics, or simultaneous vision optics. Translating vision designs are most similar to a spectacle lens bifocal and require the patient to look through the appropriate portion of the contact lens to achieve either distance or near vision. When properly fitted, they provide very good distance and near vision when the patient uses primary gaze for distance and down gaze for near. These lenses suffer from limitations to near or intermediate vision in other directions of gaze, and they are very dependent upon the proper eyelid geometry to make them function well.

Figure 1. Corneal alignment fit of Essential lens. Study Results

When utilizing a simultaneous vision design, both the distance and near fields of vision are focused on the retina, and the individual chooses which field to observe. Simultaneous designs may be aspheric power lenses, or they may have multiple concentric power zones to provide distance and near zones. Many early aspheric designs were based upon high eccentricity conic section optics and were somewhat limited in the maximal near power that could be produced. They were also highly pupil-size dependent and therefore required excellent centration, which was most often achieved by using an intrapalpebral fitting philosophy. A chief advantage to the aspheric lens is that its progressively-changing power gives it the ability to provide vision in multiple directions of gaze at all distances. Although simultaneous vision lens designs provide more flexibility for the patient than translating designs, the overall quality of vision is often reduced.

Due to the high interest level and continually-improving technology, there have been many new lens design options introduced in the past five years ­ and several of them are proving to be excellent options for our presbyopic patients.

Figure 2. Choose from three series of add powers.

This study utilized the Essential RGP Aspheric Multifocal contact lens, which is manufactured by Blanchard Contact Lens Inc. Blanchard's proprietary "S" form lathing is used to produce the posterior aspheric surface. The lens is fit utilizing a corneal alignment fitting philosophy (Figure 1) and is available in three different series of add power (Figure 2).

Study Purpose

Figure 3. Age distributions of study patients.

Patient Selection and Eligibility

Conduct of Study

1. Comprehensive baseline examination

2. Initial fitting visit

3. Dispensing visit

4. Data visits (follow-up):

Discussion

All 30 of our patients fit with the Essential RGP multifocal lens were able to continue wearing the lens until completion of the study (one month after dispensing). The mean binocular distance visual acuity was 0.04 logMAR (20/18.5) for high contrast testing and 0.18 logMAR (20/30) for low contrast testing. Mean binocular near acuity was 0.52M (20/25). With this level of acuity, as well as the good comfort reported, our patients were able to complete the study and continued wearing their lenses beyond our study time period.

Some practitioners have advocated trying up to nine different lens designs for presbyopia, since many designs have relatively modest (50 to 60 percent) success rates. For example, one study of a piggyback bifocal lens over a six-month period of time showed 50 percent of patients failing to complete the study. Of those that did completed the study, 100 percent had 20/30 or better, and 90 percent achieved J2 or better near acuity. Anderson's study of the Nova-Wet Perception multifocal RGP contact lens had 14 of 28 (50 percent) still wearing the lens at the end of the nine-month study. The Anterior Constant Focus Annular bifocal fared better with 83 percent completing a one-year study. Because these studies were performed with varying study time periods, it is difficult to directly compare any results. However, given the excellent results the Essential RGP multifocal lens has shown thus far, we believe that follow-up in one year would show a high percentage of our study patients still successfully wearing the Essential RGP multifocal lens.

The Essential RGP multifocal lens provides good distance and near acuity for a variety of distances because it incorporates aspects of both simultaneous and translating vision designs. Older aspheric multifocal designs use primarily simultaneous vision and are successful only if a well-centered fit can be achieved. Flare, especially at night, glare and vision fluctuations related to blinking and lens movement are also potential problems.

Simultaneous vision designs tend to be dependent on pupil size, sometimes allowing an inadequate or excessive range of powers to be visible at the same time. Like the Essential RGP multifocal, the Lifestyle GP multifocal and the Boston MultiVision RGP multifocal are designed to be fit in a position slightly above the pupil with corneal alignment and lid attachment. When the patient looks down to read, the lens translates upward to optimize near vision. This minimizes the image degradation as compared to using only simultaneous vision and potentially provides clear vision at both distance and near. Moreover, this design is not as limited by varying pupil size. Previous literature has suggested fitting pupils greater than 5mm with translating lenses and those smaller than 5mm with aspheric designs. The Essential RGP fits patients with a range of pupil sizes and can be fitted as either a lid attachment or intrapalpebral lens. The simultaneous vision feature of this lens design makes the lid position less critical than if it were solely a translating design.

Figure 4. The lens provided slightly better near range than spectacles.

One difficulty in employing a multifocal lens is achieving clear vision for the wide range of working distances required to meet the visual needs of patients from various occupations. For example, a high school teacher might need to see clearly at 20 feet or beyond, computer users at more intermediate range, and nurses and accountants at an even closer working distance. In this study, the Essential RGP multifocal lenses provided a near range of vision that was slightly better than the patients' spectacle bifocal add (36.80cm vs. 30.09cm) (Figure 4). It might be of interest to note that this near range was measured in the phoropter in primary gaze for both the spectacle add and for the contact lenses. Therefore, we might reasonably expect this range to be extended even more when the patient is allowed to change gaze and maximize the add power of the contact lens with some upward contact lens translation.

The lens is available in three add power series. During the study, we found that the Series 1 add is rarely used except for the occasional first-time presbyope. The Series 2 and 3 add powers are similar; however, the add is located closer to the center of the lens with the Series 3 and farther with the Series 2. The Series 3 add power is best used to optimize near acuity when the patient cannot achieve better then 20/40 near acuity with a Series 2 lens or in cases of lens decentration.

Besides simultaneous and translating vision optics, monovision is a third mechanism that is frequently utilized to achieve a near add power while wearing contact lenses. In this modality, one eye is over-plussed relative to the other so that one eye will see well at near, and the other will see well at distance. Because of the power disparity between the two eyes, stereopsis is frequently reduced, and glare with night driving is also often a problem. With higher add powers, intermediate vision is often compromised as well. The mean stereoacuity with the Essential RGP multifocal lens in this study was 28.58 seconds of arc. If this fact is combined with good distance visual acuity in both eyes and the ability to see at both near and intermediate distances, the Essential RGP multifocal becomes a very good alternative to monovision.

The Essential RGP multifocal is an aspheric lens designed to perform optimally with a lid attachment fit, centered just above the center of the pupil and an alignment lens-to-cornea relationship; however, lenses that show some decentration will often still provide acceptable vision for the patient. This lens design is much less sensitive to lateral decentration than a purely simultaneous vision design. A fitting tip to consider is that when the optimal fit cannot be achieved, it is often necessary to move up to the next higher add power series to optimize visual performance. If a patient is currently wearing a lid-attached single vision RGP lens successfully, this lens is often very simple to fit. It will usually be fit slightly steeper than the single vision lenses and appear to have more edge lift. Handheld trial lenses should be utilized to determine the maximum plus power at distance for each eye and then demonstrated at both distance and near with both eyes open. It is important to note that small changes in power (0.25D steps) can make a dramatic difference in best near visual acuity.

This study has demonstrated that the Essential RGP multifocal contact lens can be successfully fit on a wide range of patients. The lens is fairly simple to fit, especially on current single vision RGP wearers. It provides very good distance, intermediate and near vision and is a viable lens of first choice for both early and mature presbyopes.

To receive references via fax, call (800) 239-4684 and request document #77. (Have a fax number ready.)

Dr. Gromacki is a faculty member at the Department of Ophthalmology and Vision Sciences at The University of Michigan.

Dr. Badowski is assistant professor of clinical optometry at the College of Optometry at The Ohio State University.

Dr. Wicker is a faculty member at the Department of Ophthalmology and Vision Sciences at The University of Michigan.

Dr. Ventocilla is in private practice in Perry, FL.

 


Contact Lens Spectrum, Issue: December 2001