An Evaluation of Presbyopic Correction Modalities

Jason G. Jedlicka, OD, Sandy Yee, OD, & Kenneth Daniels, OD
JUNE 1998

This study assesses the performance of the SoftSite multifocal
lens in comparison to three other types of
presbyopic correction.

Current data reveals that about 40 percent of the U.S. population is presbyopic and that this number will increase to 45 percent by the year 2000. This segment of the population is clearly growing fast, and many of these patients already wear contact lenses. Encouraged by this outlook and spurred by new technology, manufacturers and designs of multifocal contact lenses are becoming more plentiful.

In the past, multifocal hydrogel lens fits were a gamble, with success rates ranging from 37 to 65 percent. Traditionally, soft multifocal lenses superimposed blurred images over clear images, creating a ghosting or doubling effect and reducing acuity and contrast sensitivity at all distances. Today, design improvements are yielding success rates of between 71 and 80 percent, indicating that a growing number of patients can be successfully fit with one of the many lenses now available. Nevertheless, multifocal soft contact lenses for presbyopia still tend to be underutilized by eyecare practitioners. Most presbyopes who want soft contact lenses end up with monovision or with distance vision lenses and reading glasses. While both options are acceptable, multifocal contact lenses or modified monovision may serve certain patients better.

SoftSite is an aspheric daily wear lens manufactured by Unilens Corporation (Largo, Fla.) in 38 percent water content polymacon material. It is designed with multiple aspheric curves in its front surface to provide a higher center near add and a full range of uninterrupted vision from distance to near. The labeled power represents the center of the lens, thus the area of most plus power. Available base curves are 8.4mm and 8.7mm, the diameter is 14.5mm, and powers range from +8.00D to -8.00D in 0.25D steps.

Through the Contact Lens Research Program of the Pennsylvania College of Optometry, we performed this single-masked, prospective pilot study to determine the effectivess and acceptability of the new SoftSite multifocal lens, and to compare its objective and subjective visual performance to that of spectacle correction, monovision and modified monovision (using one single vision lens for distance and one SoftSite multifocal lens for distance and near). We had also hoped to identify the characteristics of a patient who would accept correction with the SoftSite contact lens.

The Participants

We randomly selected candidates from the pool of current presbyopic soft contact lens wearers at The Eye Institute of the Pennsylvania College of Optometry. Twelve patients enrolled and 10 completed the study; one was lost to follow-up after the initial visit and another chose not to participate because she couldn't be satisfactorily corrected at the initial visit. Optical criteria included distance ametropia of greater than �0.75D with a range of -8.00D to +6.00D and refractive cylindrical correction of 0.50D or less.

All study participants were female, wore soft contact lenses at least five days per week on a daily wear basis and had no evidence of physiological compromise or pathology (Table 1). Every patient had a fused crossed cylinder of between +1.75D and +2.25D, within the fitting criteria for the SoftSite multifocal contact lens. All were correctable to 20/20 OD and OS, except for one patient who had a best distance correction of 20/30 in her left eye and another patient who had best distance correction of 20/25 OD and 20/30 OS.

Methodology

At the initial visit, we gathered all spectacle correction data and dispensed SoftSite multifocal contact lenses OU to all patients, with power and base curve determined by the manufacturer's guidelines. We performed testing with the multifocal lenses and scheduled the patients for a two-week follow-up. At the second visit, we repeated all testing with the SoftSite lenses and made appropriate changes to the lens parameters if overrefraction or examination revealed potential for improvement in fit or visual acuity. We then scheduled the patients for another two-week checkup.

At the third visit, we placed all patients in the modified monovision mode. Patients wore the SoftSite multifocal lens in the nondominant eye for near and a lens made from their habitual lens material in the dominant eye for distance. We then repeated all testing and scheduled the patients for a two-week follow-up.

At the fourth visit, we refit all patients into monovision using their habitual lens materials. We optimally corrected the dominant eye for distance and the nondominant eye for near and repeated all testing. The same distance lens was used in both the modified monovision and the monovision trials. For those not wearing monovision lenses upon entering the study, we dispensed appropriately fit disposable lenses for each eye. We instructed all patients to wear the study lenses for as long as they felt comfortable. They all used ReNu Multipurpose Solution with weekly enzyming to clean and store the lenses, and they used rewetting drops as desired for comfort or visual improvement.

The testing procedure at each visit was the same and consisted of: visual acuity at distance, recorded at six meters from a Bailey-Lovie logMAR acuity chart; near vision, tested at 40 centimeters with a Lighthouse Near Visual Acuity Test; Modified ETDRS with Sloan Letters (Lighthouse Low Vision Products, Long Island City, N.Y.); overrefraction; best corrected acuities; near point testing; stereopsis with Randot stereo circles (Stereo Optical Company, Chicago, Ill.); low contrast visual acuity at distance with a Bailey-Lovie #6 chart; assessment of lens fit; and corneal topography on the Tomey TMS 2 system (Tomey Instruments, Cambridge, Mass.). For the spectacle evaluation, we performed all exam room testing through a trial frame containing the correction obtained at the initial visit.

At each visit, patients filled out a survey containing questions about their wearing habits and about the level of performance of the correction they were wearing while at home, at work, shopping, at a computer and driving. Also included were questions regarding quality of lighting at home and at work, vision at night versus day and whether they would continue in that mode of correction. Where applicable, participants rated the performances on a scale of 0 to 100 using a Visual Analog scale. At the final visit, we gave them the last survey to take home and mail in after two weeks of monovision wear.

Survey Results

Table 2 illustrates patient ratings for each modality based on the survey results. For most categories, spectacle correction subjectively gave the highest quality of vision. Among the soft lens corrections, patients generally preferred the SoftSite lens for intermediate and near work, but rated it poorest at distance. Predictably, patients noted best distance vision quality with modified monovision. In the categories of day and night wear, both driving and in general, there seemed to be little difference in preference among all lenses, but patients rated modified monovision higher than the other modalities for night driving and overall night vision.

We determined that a mode of correction was acceptable for a patient if that patient was willing to continue in it after the conclusion of our study. All 10 participants were satisfied with their spectacle correction but preferred contact lens wear. Seven participants said they would continue with the SoftSite lenses OU after our study, while five said they would continue with modified monovision and five said they would continue with monovision. Two patients said they would not wear any contact lens correction other than distance vision only (DVO) contact lenses with reading glasses.

With respect to comfort and lens tolerance, nine patients found the study lenses to be comfortable and easy to handle and reported average wearing time as consistent with previous lens wear. Most patients used rewetting drops once or twice daily with the SoftSite lenses. One patient experienced mild subjective discomfort with the study lenses and less wearing time than she had with her previous lenses. There were no lens wear complaints with monovision or modified monovision among patients who were in the same lens material they wore prior to the study.

Exam Results

This study confirmed what others had concluded -- that overall visual acuity is slightly degraded with a multifocal lens. Even with adjustments to the multifocal lens power at the second visit to optimize distance vision, the acuity remained virtually the same. Nearly all patients accepted additional minus power at distance with the SoftSite lenses when fit according to manufacturers guidelines, with four patients requiring a change of one or both lenses due to unacceptable distance blur. Average overrefraction at the SoftSite two-week follow-up was -0.40D OD and -0.30D OS, with near vision minimally affected by this change. Spectacle acuity was good at distance and at near, and eyes with single-vision lenses were comparable to spectacle acuity at corresponding distances. Not surprisingly, we also found a correlating drop in acuity with monovision and modified monovision when testing at distances for which the lenses did not correct (Table 3).

Corneal topography measurements were consistent and stable throughout all visits. All lenses achieved an acceptable fit and good centration and movement with base curve selection specified by the manufacturer. All SoftSite lenses moved 0.5mm to 1.0mm with blink in primary gaze and centered well. We noted no objective adverse effects (i.e., corneal staining) secondary to lens wear. One patient lost a lens the day before her second visit, which was replaced immediately, but no study lenses were torn.

Factors for Achieving Success with Presbyopic Correction

In theory, age, refractive error, personality and occupation all seem to be potential factors for success or failure with a particular mode of presbyopic correction. In this study, the ages of those who were not successful with each lens modality were variable, and we detected no correlation. Included in those failing with the SoftSite contact lenses was a moderate myope, a low myope and a moderate hyperope, indicating that success is not based on refractive error. We also found no measurable correlation between success and pupil size.

Although the occupations of the three patients who disliked multifocal correction were completely dissimilar, occupation is surely a concern when screening presbyopic candidates for soft contact lenses. Our study group consisted mostly of working women who need distance, intermediate and near vision at work. The five patients who spent a large portion of their work day on a computer were all pleased with the SoftSite lens, reaffirming the fact that good intermediate vision is often a benefit of an aspheric lens design. Thus, we determined that the patient base, despite its size, was a good cross-section of potential presbyopic contact lens wearers.

It was purely coincidental that no males were included in the study. It is generally assumed that men and women have different expectations of vision correction. It's likely that a group of 10 male participants with the same objective data may have given us very different subjective results. However, our study does have clinical value because women tend to comprise the vast majority of patients interested in this type of correction.

Cost is certainly a major factor for those who might consider a multifocal lens. The fact that these lenses were given to patients at no cost undoubtedly brought participants into the study who otherwise would not consider this lens modality. It's important to follow-up on these patients in 12 to 24 months to see how many of them purchased another pair of SoftSite lenses after our pilot study ended. Since our study showed similar subjective and objective results with monovision when compared to SoftSite lenses, monovision may be an adequate alternative for patients who don't wish to pay the higher cost of multifocal lenses.

This study also revealed that personality and motivation for all correction modalities was crucial. Five of the six patients who did not accept monovision correction entered the study in one of the other modes of correction (Table 4). Perhaps these patients had tried monovision in the past and failed, which would explain their dissatisfaction in this study. Furthermore, the three patients who ultimately did not like the SoftSite lenses entered the study with the most cynical outlook on their odds for success and were clearly the most difficult to please during the fitting process. They needed to be reminded of their appointments, had to be rescheduled at times and were often late for their follow-up visits. The seven participants who were successful with SoftSite lenses were pleasant to work with, kept their appointments, were on time for visits and were patient while adjusting to the lenses. We also found that the patients who did not like the SoftSite lenses usually did not like any other method of soft lens correction other than the lenses they were wearing when they entered the study. Most of those who did like the SoftSite lenses also accepted monovision or modified monovision correction.

Factors for Success With SoftSite

Our study found that the SoftSite lens is comfortable and easy to handle and that it provides surprisingly good acuity at all distances. It compared favorably to other corrective options for presbyopes, especially for those who are motivated and those for whom cost is not an issue. Most study participants favored the feel of the SoftSite compared to their prior lens material. The ocular health and topography showed no adverse effects from lens wear. We found the manufacturer's guidelines easy to use and predictable, with no more than one exchange needed to achieve a successful fit on the seven patients who liked the lenses. We did detect about one line of acuity lost at distance with the multifocal lens OD and OS versus spectacles or single-vision lens correction. Despite this, many patients preferred SoftSite, citing what they believed to be a more "natural" feel to the vision. When we consider the acuity gained by positive binocular summation (demonstrated by Pirenne in 1943), where binocular acuity is measured as better than the better eye monocularly, we understand this response.

According to other studies, near vision has often been a weak aspect of soft multifocal lenses. SoftSite is designed for patients needing near addition of +1.75D to +2.50D, and it worked well on patients from their early 40s through their late 50s. Of those who did not find the SoftSite to be acceptable (Table 5), one had subjective discomfort at times, another noted difficulty focusing on objects and sustaining a clear image, and the third was a borderline presbyope who was 20/15 with her current lenses and perceptive of even the slightest image degradation. All of these patients required a change in lens power at the first follow-up visit, reporting poor distance acuity. It is interesting to note that the only patient who enrolled in the study but could not be successfully fit was also a borderline presbyope with some accommodative system problems. Although there was a third borderline presbyope who was happy with the SoftSite lenses, she was anxious to change out of monovision and actually had a loss of two to three lines of acuity with the study lens as compared to her spectacles. This suggests that the SoftSite lens is not the lens of choice for the early presbyope but is more suitable for patients who cannot obtain the near correction they need with other lower aspheric designs, such as the original Unilens, a center near, front aspheric soft lens designed by Unilens Corporation for patients with near demand up to +1.75D. SoftSite seems to be an excellent option for the mature presbyope who needs more near power or is trying multifocals for the first time (Table 6). For those with higher distance demands, modified monovision may prove to be the best option.

With any pilot study, trends can be found or missed based on limitations of the patient base. A small study size, a population of all women, and contact lenses provided free of charge to the participants all tend to skew the information and somewhat bias subjective results. Therefore, we intend to continue to analyze the SoftSite lens on patients as the opportunity arises. A good history will elicit the patient's priorities and indications of motivation and reasonable expectations, which are the most crucial pieces of information in deciding which presbyopic soft lens option to pursue.

This study was partially funded by Unilens, Inc. The authors are not paid consultants for the company.

The authors would like to express their sincere appreciation to Giovanna Olivares, O.D. (Unilens), Dave Braun, Steve Zadel, Rosario Vallejo and Peggy Giordano for their assistance.

To receive references via fax, call (800) 239-4684 and request document #37.

Dr. Jedlicka, recipient of the 1997 Arthur Giroux Award for optometry residents, is completing a fellowship in cornea, glaucoma and refractive surgery at Minnesota Eye Consultants, Minneapolis, Minn.

Dr. Yee is the Cornea and Contact Lens Resident at State University of New York College of Optometry.

Dr. Daniels is an assistant clinical professor and director of the Contact Lens Research Program at the Pennsylvania College of Optometry. He is in private practice in Hopewell, N.J.