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.

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.

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.

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).

1. Comprehensive baseline examination

2. Initial fitting visit

3. Dispensing visit

4. Data visits (follow-up):

* Performed one week, three weeks and four weeks following the dispensing visit.
* Testing included: high and low contrast Bailey Lovie visual acuity, near Bailey Lovie visual acuity, Randot stereoacuity, measurement of binocular range of clear near vision, contact lens fit evaluation and slit lamp evaluation with fluorescein.
* New fit patients were given an adaptation period and a follow-up visit prior to initiating the data visit schedule. If they were not able to achieve a minimum of 10 hours of wearing time per day, they would have been discontinued from the study.

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.

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

SPONSORED BY

Attaining clear near vision as well as crisp distance vision in multifocal RGPs for the moderate to high presbyope can be challenging. We evaluated the one-month clinical performance of the Blanchard Essential RGP Aspheric Multifocal for patients requiring greater than a +1.75D spectacle reading addition.

Study Overview

Thirty subjects were enrolled in the study. While the Essential design comes in three series offering varying degrees of presbyopic add correction, we evaluated only two of the lens types. Some 14 of the subjects (47 percent) received Series II lenses, and 16 of the subjects (53 percent) received the Series III design. Of the 30 subjects that entered the study, 26 (87 percent) completed the study, wearing the lenses for the one-month time period. Ninety-two percent of the subjects attained a distance visual acuity of 20/20 or better and a near visual acuity of 20/25 or better. At the completion of the study, subjects were given the option of receiving either Essential lenses or financial compensation similar in value.

Study Methods

Subjects. Thirty adapted subjects, all habitual RGP lens wearers, joined the study. The mean age of the seven males and 23 females enrolled was 53 years, ranging from 45 to 63. The mean spherical equivalent was -3.14D, ranging from +2.50D to -6.94D. Eighteen of the 30 subjects enrolled (60 percent) required a moderate spectacle addition of +1.75D to +2.00D, and 12 (40 percent) required a high spectacle addition of +2.25D to +2.50D. Four patients dropped out of the study: two with a moderate spectacle addition and two with a high spectacle addition.

Lenses. The Series II lens fits patients with adds from +1.50D to +2.25D (Figure 1). The Series III lens fits patients with adds of +2.50D or greater (Figure 2). All lenses were evaluated to the higher add powers in the subject group. The lenses were dispensed in a power range of +3.00D to -7.75D, with base curves ranging from 7.20 to 8.30mm.

Design. Each subject wore the contact lenses for a period of one month on a daily wear basis. We evaluated the lenses for visual acuity (both distance and near), lens positioning and movement, ocular response and patient acceptance.

Procedure. We determined patient eligibility using the criteria defined in the referenced study protocol. At the initial examination, a fitting set determined the initial lens parameters. At the dispensing visit, the subjects received instructions on contact lens wear, care and handling, and were advised to wear the lenses on a daily wear basis. Subjects used Boston Advance Cleaner and Boston Advance Comfort Formula Conditioning Solution to care for their contact lenses. Follow-up examinations occurred at one week and one month from the date of dispense. The study took approximately five months with final results compiled in the spring of 2000.

Lens Fit. Of the 30 study subjects, 17 (57 percent) were successfully fit with the initial lens order requiring no subsequent changes to enhance comfort, fit or visual performance. Thirteen subjects (43 percent) required a lens reorder (Figure 3). Reasons for lens reorder included base curve/diameter change (50 percent), power (44 percent) and comfort enhancement (6 percent). An average of 2.6 lenses was required for the entire study population to receive two lenses illustrating proper lens fit and acceptable visual acuity. All four of the subjects that chose to discontinue from the study needed at least one lens reordered.

Success of Lens Wear

One measure of success is the percentage of subjects that completed one month of wear. Twenty-six of the 30 subjects enrolled (87 percent) completed one month of lens wear (Figure 4). Of those completing one month of wear, 22 subjects (85 percent) chose to receive the lenses over financial compensation of similar value.

Distance Visual Acuity. At the one-month visit, two subjects (8 percent) achieved a distance visual acuity of 20/15. Twenty-two (84 percent) achieved 20/20, one (4 percent) achieved 20/25 and one (4 percent) achieved 20/30 (Figure 5). For purposes of analysis, distance visual acuity was converted to Snellen VA from LogMAR notation. There was no significant difference in the mean distance visual acuity over time. Mean LogMAR distance visual acuity was 0.01 at dispense, 0.01 at one week and 0.00 at one month (approximately 20/20).

Near Visual Acuity. At the one-month visit, two subjects (8 percent) achieved a near visual acuity of 20/15. Seventeen (65 percent) achieved 20/20, five (19 percent) achieved 20/25, one (4 percent) achieved 20/40 and one (4 percent) achieved 20/50 (Figure 6). There was no significant difference in the mean near visual acuity over time. Mean LogMAR near visual acuity was 0.05 at dispense, 0.05 at one week and 0.04 at one month (approximately 20/20+2).

Slit Lamp Findings. Compared to baseline, we saw no significant differences in the mean findings over time for corneal staining, limbal injection, tarsal conjunctival abnormalities and anterior segment abnormalities. Bulbar injection showed a statistically significant decrease (p=0.032, ANOVA) over the duration of the study. No positive findings were noted on the slit lamp examinations for epithelial edema, epithelial microcysts, corneal neovascularization, corneal infiltrates, corneal striae, conjunctivitis or the external adnexa.

Comparison of Series II and Series III. The Series II and III contact lenses performed very similarly in most categories at the one-month visit. The performance in distance visual acuity and near visual acuity was very similar, as were the patient assessments of the quality of distance and near vision. The success rate with the Series II lens was 93 percent versus 81 percent for the Series III lens. Of those patients that completed one month of contact lens wear, 92 percent of those wearing the Series II design chose the lenses over financial compensation, while 77 percent of those wearing the Series III design chose the lenses.

Discussion

The Blanchard Essential RGP Aspheric Multifocal contact lens performed well in most categories. This lens provided excellent distance and near visual acuity for most patients in both the Series II and Series III designs. There was an excellent success rate with 26 of 30 subjects enrolled (87 percent) completing one month of contact lens wear. Patient assessment scores generally rated the lens to be excellent or good in most categories. There was a trend towards corneal flattening and refractive changes in some patients, a finding that has been previously noted in the literature with many RGP aspheric multifocal contact lenses.

Dr. Businger is in private practice in Luzern, Switzerland, and provides technical evaluation and analysis of contact lenses and related products for numerous corporations.

Dr. Byrnes is in private practice in Londonderry, New Hampshire, and is a faculty member of the New England College of Optometry/Contact Lens Department.

Dr. Baker is in private practice in Lafayette, Calif., with an emphasis on contact lenses. He is a member of the clinical faculty at the University of California at Berkeley.

his article will focus on gas permeable bifocal/multifocal contact lens designs in general. It will also delve into the specifics of the Essential GP aspheric multifocal design and changes that have been made to that design. A recent study has shown that changes to the original Essential GP aspheric multifocal GP design have improved distance and intermediate vision as well as comfort, while at the same time reducing spectacle blur.

MULTIFOCAL LENS DESIGNS

As a review, there are two bifocal/multifocal contact lens designs: translating, also known as alternating vision, and simultaneous vision. With alternating vision lenses, the top of the lens usually contains the distance vision area, and there is a line where the near area engages in the lower portion of the lens. This is an easy concept to explain to the patient because bifocal eyeglasses work the same way, and patients visualize them when we discuss bifocal contact lenses.

Theoretically, in straight ahead gaze, patients see well at distance and when the patient looks down, the lens translates up so the near correction covers the visual axis. With some designs, the image jump experienced with many bifocal eyeglasses is eliminated when moving from the top distance area to the bottom near area of the lens. For some patients, this can make translating bifocal contact lenses easier to adjust to than bifocal glasses. However, patients generally lose intermediate distance focus with translating bifocal contact lenses.

With the simultaneous vision design, theoretically the retina receives input from multiple distances at the same time with different clarity of the images. The visual system and brain must determine which image is most important and adjust to obtain good vision at a particular distance. Some translation may occur, and many newer GP lenses rely on this to enhance the image at all distances. Simultaneous vision design multifocal lenses can be concentric, aspheric or diffractive. I will discuss only aspheric designs here.

Aspheric designs use an aspheric front or back surface to create the multifocal effect. As a rule, front surface aspheric designs are center-near and back surface aspherics are center-distance. Each type has its own merits, as center-near designs favor near and intermediate vision, while center-distance lenses usually give better distance focus.

The Tangent Streak (Fused Kontacts) is the prototypical translating GP bifocal. It looks like an executive spectacle bifocal with a flat segment on top which runs from edge to edge. The segment height and add power vary, and a truncation and prism ballast are ordered. The Metro-Seg (Metro Optics) is a crescent-shaped bifocal design which offers unlimited add powers and a thinner overall lens. Most translating/alternating designs deliver marginal intermediate-distance vision due to the two-zones. They are sometimes less comfortable due to greater mass and thicker, truncated bottom edge.

Many simultaneous GP multifocals are available. Aspheric designs make up the bulk of this category. Earlier generation lenses had very steep base curve-to-cornea fitting relationships and high eccentricity values. They sometimes led to severe corneal molding and a difficulty transitioning from contact lens to spectacle wear, known as spectacle blur. Newer versions of aspheric designs generate the same near power with lower e-values and more normal fitting relationships along with less corneal molding and spectacle blur. Most aspheric lenses need to translate up on downgaze to take advantage of the near power found in the mid-periphery. Aspheric lens designs also seem to provide better intermediate vision than their translating design counterparts.

The Essential GP Multifocal (Blanchard Contact Lens, Inc.) is a newer generation design and is fit much like a conventional single vision GP with an alignment fitting philosophy. This lens is manufactured using proprietary S-Form lathing technology which allows for add powers beyond the +1.50D to +1.75D range often stated as the maximum add power for these designs. The Essential GP is available with three different add series, and can correct adds of +2.50 and more. The lenses are fit using an alignment fitting philosophy, which, in theory, should reduce the corneal molding often seen in earlier generation aspheric GP multifocals. This does not mean that there are no corneal topography changes with this lens. Corneal changes and spectacle blur are seen in some patients. The design changes incorporated into the new Essential Xtra target this.

STUDY DESIGN

We began a study earlier this year to evaluate what effect, if any, would be seen with the changed posterior surface aspheric geometry on the Essential Xtra. Eight offices participated in this study, which began with 40 subjects and ended with 36 participants (four patients lost to follow-up). Existing Essential GP wearers were randomly recruited to wear the study lenses and compare performance of the two designs in real-life conditions.

The study lenses incorporated a modified S-Form posterior surface aspheric geometry that was steeper throughout the entire base curve. This creates a posterior surface in the paracentral area of the lens that has less bearing on the cornea, which should result in less corneal flattening. The steeper geometry also lowers axial edge lift, which makes the lens more comfortable. It also minimizes lens to lid interaction which allows the lens to center better. The posterior S-Form geometry change also begins farther away from the axial center of the lens than in the original design, creating a larger distance optic zone in each add series. This should allow patients to be moved to the next stronger lens add series without a negative impact on distance vision.

As a further design twist, one pair of study lenses was manufactured using Boston ES (Polymer Technology), the usual polymer for the original Essential GP, and a second pair was made using Boston XO (Polymer Technology), the specified polymer for Essential Xtra. Each patient wore the pair of the Boston ES study lenses for a period of two weeks and the study pair in the Boston XO material for an additional two-week period.

At the beginning study visit, subjects were evaluated for their subjective assessment of the performance of their current Essential GP lenses, including the presence or absence of spectacle blur, vision with the contact lenses and comfort. They were also evaluated at the slit lamp for lens fit, with and without fluorescein, position and movement, and for any external pathology. Keratometric readings and/or corneal topography were also performed.

Next, the first pair of study lenses, in Boston ES, were applied and allowed to settle. Subjective vision and comfort comments were elicited and vision measured at distance, intermediate and near. The fit of the study lenses was evaluated at the slit lamp, with and without fluorescein. Proper cleaning and handling was reviewed, and the subjects were instructed to wear the study lenses as they had worn their original Essential GP lenses. Subjects were seen in follow-up two weeks later, at which time the second pair of study lenses, in Boston XO, was dispensed following assessment of pair one.

STUDY RESULTS

At study conclusion, results were tabulated as presented here. All of the subjects in the study reported distance vision with the study lenses that was equal to, or better than, their original lenses.
The majority of study participants also noted improved or equal vision with the study lenses at intermediate-distance . Thirty-one patients (89 percent) reported intermediate vision performance equal to or better than their current Essential GP lenses with Essential Xtra study lenses. Five patients (14 percent) preferred intermediate vision performance of their existing Essential GP lenses.

Some 78 percent reported near vision with the Essential Xtra study lenses equal to, or better than, their original lenses. Eleven patients (31 percent) reported near vision equal to their current lenses, 17 patients (47 percent), reported near vision better than their current Essential GP lenses, and eight patients (22 percent) preferred near vision performance of their existing Essential GP lenses
Comfort with the study lenses was preferred by 89 percent of the subject population with 32 subjects reporting comfort equal to or better than their current lenses, and four patients eleven (11 percent) reporting the original design more comfortable.

Spectacle blur was the last area evaluated for this study. We expected that the study lenses with the new posterior surface configuration in the Essential Xtra lens design, in either Boston XO or Boston ES materials, would show less corneal molding than the original Essential GP design in Boston ES material. Eighteen of the study participants (50 percent), stated they had no spectacle blur with either lens design. Of the remaining 18 subjects, 17 (47 percent), reported an absence of or significantly reduced occurrence of spectacle blur with one patient reporting no change or reduction in spectacle blur over their current Essential GP lenses. Thirty-five subjects (97 percent) of the total study population, reported minimal or no spectacle blur with the new Essential Xtra lens design.
Overall, the Essential Xtra study design with the new steeper posterior surface aspheric geometry, was a success. Distance and intermediate vision was improved or equivalent to the original Essential GP design. Comfort was better with the study lens design and for patients exhibiting spectacle blur, it was reduced or eliminated with the study lenses.

In a small, informal study done after the conclusion of the aforementioned study, I randomly selected the first four Essential GP wearers to present at the office and reordered their current Essential GP parameters in the new design. These patients wore the Essential Xtra, with the new steeper posterior surface aspheric geometry in the Boston XO material for one month prior to reevaluation. At follow-up, all four participants reported better vision at all distances, better comfort and no spectacle blur. Each patient also had steeper keratometric readings after wearing the new design, further showing the reduced corneal flattening of the new design versus the original.

CONCLUSION

From these studies, we concluded that the Essential GP multifocal continues to evolve. New presbyopic patients can enjoy good vision at all distances, good comfort throughout their wearing day and an easier transition from contact lens wear to spectacle wear from day one. Existing Essential GP wearers can be changed to the new Essential Xtra by simply reordering their current parameters in the enhanced design without the added chair time of refitting. As patients age and their add requirements increase, the next higher add series in the Essential Xtra should give the near vision boost desired without changing distance vision or lens performance.

The following practitioners contributed to the study: Charlene Hanes, OD, FAAO; Sarah Marable, LPN, LDO; Keith Davis, OD; Carl Edler, OD; Rhonda Robinson, OD, FAAO; Chris Smiley, OD; Amy Ice, OD.

Dr. Benoit practices in Concord, N.H., as part of a multi-subspecialty ophthalmology group. He is a Diplomate of the Section on Cornea and Contact Lenses of the American Academy of Optometry.

THE ORIGINAL ESSENTIAL GP VS. THE IMPROVED ESSENTIAL XTRA DESIGN.
By Stephen P. Byrnes, OD, FAAO

Case #1 Fitting the monocular, hyperopic, astigmatic, presbyope

This 7.50D base curve, 9.5mm lens diameter, Essential Series III GP multifocal lens has a small distance optic zone that allows for quicker translation into the intermediate and near optic zones. Translation to intermediate and near zone is created by the S Form aspheric curve. The relative flattening produced by the S Form aspheric back surface design creates excessive peripheral clearance and a potential for unwanted lens decentration. Decentration of the small distance zone can result in unstable distance vision performance.

Fluorescein pattern analysis reveals a small zone of central clearance created by the spherical distance optic zone. The two mid-peripheral bearing zones at 2 and 9 o'clock position the lens temporally relative to the visual axis. A wide band of peripheral clearance is noted from 2 to 9 o'clock, with excess pooling at 5 o'clock created from lid-induced lens tilt and excessive peripheral clearance.

The patient is very visually demanding, requiring excellent distance and intermediate vision and good near vision. She is a monocular patient with an amblyopic left eye. The patient complains of unstable distance vision, particularly during night driving.

Compare the 7.50D base curve, 9.5mm lens diameter, Essential Xtra Series III lens on the same eye. The improved Essential Xtra design has an expanded distance zone that improves distance vision particularly in low illumination or if the lens has decentered relative to the visual axis. The S-Form aspheric curve is compressed, narrowing the intermediate zone, allowing for quicker access to the near zone. The relative flattening produced by the S Form aspherics on the back surface is reduced. The potential for unwanted corneal change is minimized, reducing the severity and/or occurrence of spectacle blur upon transition to spectacle wear. Less peripheral clearance is created and lens centration is improved.

Fluorescein pattern analysis reveals minimal central clearance feathering into two enlarged zones of mid-peripheral alignment that hold the lens in a more centered position relative to the visual axis. Peripheral clearance is reduced and there is mild pooling at 5 o'clock due to lid induced lens tilt .

The patient's visual demands have been met with this lens. The patient is very satisfied.

Case #2 Re-fitting the Monovision Patient

This 7.40D base curve, 9.2mm lens diameter, Essential Series II Standard lens positions superior/temporal. It decenters relative to the visual axis. The pupil can be seen just left of the light reflex (Figure 3). In order for the patient to attain good distance vision, she must be over-minused because she is looking through the intermediate vision zone. Over-minusing the patient reduces the available add effect.

Fluorescein pattern analysis reveals central pooling with mid-peripheral alignment and excessive peripheral clearance. The wide area of peripheral clearance narrows the mid-peripheral alignment zone, creating an unstable lens that slides off center and drops to an inferior-temporal position between blinks.

This patient has been refit from monovision to multifocals in order to improve her overall binocular vision. She is disappointed with distance vision attainable with this lens design when compared to her single vision GP lenses.

We compared a 7.40D base curve, 9.2mm lens diameter, Essential Xtra Series II on the same eye. The lens positions superior/temporal and is more centered relative to the visual axis than the original Essential GP lens design. The pupil can be seen just left of the light reflex. This lens has a wider central distance zone which allows for some lens decentration while maintaining accurate distance focus. The S- Form aspheric curve is compressed, reducing the area between the distance and near zones.

Fluorescein analysis demonstrates mild central pooling that feathers into mid-peripheral alignment. The peripheral clearance zone has been narrowed, enlarging the area of lens alignment . This creates a more stable lens fit that maintains position after the blink, producing stable and accurate vision.

Distance vision has improved to "about the same" as her single vision distance monovision lens. However, the patient now sees equally well at all distances with either eye. Binocular performance has improved at distance, intermediate and near ranges.

Distance vision has improved to "about the same" as her single vision distance monovision lens. However, the patient now sees equally well at all distances with either eye. Binocular performance has improved at distance, intermediate and near ranges.

ESSENTIAL | FITTING GUIDE | CLINICAL STUDIES | TROUBLESHOOTING GUIDE