Multifocal Lenses: Presbyopia and Beyond
BY DAVID A. BERNTSEN, OD, PHD, FAAO
In his February 2014 Editor’s Perspective, Dr. Jason Nichols commented on the low percentage of multifocal contact lens fits reported in the 2013 International Prescribing report (Morgan et al, 2014), despite growing numbers of presbyopic patients. While multifocal fits made up only about 12% of all fits overall in 2013, the number was even lower in the United States (9% to 10%).
So why aren’t more presbyopic patients being fitted in multifocal lenses? While presbyopes may drop out of lens wear due to comfort issues, the development of new, innovative materials with properties intended to address these issues has continued. Compromised vision or complexity in fitting compared to other presbyopic contact lens options such as monovision are also frequently mentioned as reasons for not fitting more multifocal lenses.
While eyecare providers will develop their own opinion of a particular multifocal lens design, what does the clinical literature tell us about multifocal contact lenses and vision?
Monovision Versus Multifocal
While many new multifocal designs are now available, the percentage of multifocal lens fits last year suggests that many presbyopic patients are being fitted with spectacles or with monovision. Several studies have compared visual acuity when wearing multifocal contact lenses to either monovision or spectacle correction. Multiple multifocal contact lens designs have been evaluated including bilateral designs (e.g., wearing a center-near lens on each eye) and modified designs, in which a center-distance lens is worn on the dominant eye while a center-near lens is worn on the nondominant eye.
Despite the different optical designs of each manufacturer’s multifocal lenses, the visual acuity results across studies are fairly consistent, with most studies finding no change in binocular high-contrast visual acuity at distance or near compared to spectacles with either two center-near lenses (Richdale et al, 2006) or with one center-distance lens and one center-near multifocal lens (Ferrer-Blasco and Madrid-Costa, 2011; Fernandes et al, 2013).
Contrary to these studies, a recent study by Gupta et al (2009) did report that high-contrast distance vision was three letters better, and high-contrast near vision was one line better with monovision than when the same patients were fitted with either two high-add or two low-add center-near multifocal lenses. Given the better multifocal visual acuity results by Richdale et al (2006) using a very similar center-near design when allowing for mixed adds (a low add in one eye and a high add in the other), it is possible that biasing one eye for distance and one eye for near might have contributed to the differences in visual acuity between the studies. Interestingly, Fernandes et al (2013) also reported that there was a significant improvement in monocular high-contrast near visual acuity in eyes wearing a center-distance lens and improved monocular high-contrast distance acuity in eyes wearing a center-near lens after about two-weeks of wear, suggesting that patients continue to adapt to their multifocal lenses with time.
Not all studies have measured low-contrast visual acuity, but those that have find about a one-line reduction in low-contrast visual acuity with various multifocal designs (Richdale et al, 2006; Kollbaum et al, 2013). Given the optics necessary for a multifocal lens to provide a focused image at both distance and near, this reduction is to be expected and is very similar to the reductions in low-contrast visual acuity seen with modalities such as orthokeratology (Berntsen et al, 2005). Although the one-line decrease in low-contrast visual acuity with multifocal lenses does not occur with monovision, all of the aforementioned studies that assessed binocularity found that stereoacuity was significantly better with multifocal lenses compared to monovision, and that the near range of clear vision was significantly better with multifocal lenses. Both of these findings translate into improved visual performance in a real-world setting and perhaps explain why 76% of patients in the study by Richdale et al (2006) preferred multifocals over monovision.
Another emerging application of multifocal lens designs is myopia control. New studies have been published in the last year evaluating the ability of bifocal lenses to slow myopia progression in children. Center-distance multifocal lenses are theorized to do this by causing myopic retinal defocus while still providing clear foveal vision. Lens designs with a progressive increase in plus power toward the periphery and concentric ring designs have been studied. Table 1 provides an overview of results from several studies.
|STUDY||LENS DESIGN UTILIZED||% REDUCTION IN MYOPIA PROGRESSION|
|Sankaridurg et al, 2011||Peripheral plus||34% over one year|
|Anstice and Phillips, 2011||Concentric rings||37% over 10 months|
|Walline et al, 2013||Peripheral plus||50% over two years|
|Lam et al, 2014||Concentric rings||25% over two years in all children
(50% over two years if CLs were worn ≥ six hours/day)
|Aller et al, 2006||Multi-zone||87% over one year|
|Holden et al, 2012||Peripheral plus||39% over 43 months|
Despite most studies being limited to one or two years of follow up, the results of randomized and non-randomized studies are promising. Most recently, Lam et al (2014) reported results from a randomized clinical trial utilizing a concentric ring multifocal lens design with a +2.50D add. The authors found a 25% reduction in myopia progression over two years, which is similar to the treatment effect in many progressive addition lens (PAL) studies and would not be considered clinically meaningful by most standards.
That being said, when looking only at children who wore their lenses for six or more hours per day, the researchers found a 50% treatment effect over two years. It is important to note that the dropout rate in the study was high (42%) and that we must be cautious when analyzing subgroups because some of the benefits of randomization are lost. Taking that into account, the study suggests that randomized clinical trials should continue to determine whether optical designs can be optimized to slow myopia progression.
In summary, clinical studies show that binocular visual acuity with multifocal lenses is generally similar to acuity when wearing monovision or spectacles, with the exception of low-contrast and especially low-illumination environments in which acuity tends to decrease by about one line. That being said, multifocal lenses provide a better range of clear vision at near and superior stereovision compared to monovision. While there will certainly be instances in which multifocal lenses will not perform as well as a pair of spectacles (e.g., dim environments), they provide presbyopic patients with a glasses-free option under the majority of circumstances. With the continued investigation of multifocal lenses for myopia control, we may find even more reasons to reach for multifocal lenses in the future. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #222.
Dr. Berntsen is an assistant professor at the University of Houston College of Optometry. He has received research funding from the Johnson & Johnson Vision Care Institute and Alcon.