Bifocal and Multifocal Eyeglasses and Myopia Control
“Bifocals” or “Multifocals” are lenses that are designed to provide the proper distance prescription when viewing distance targets and a lower near prescription when looking lower to read or use a computer. It has been suggested that the accommodative response described previously may play a role in progressive myopia. If the accommodative response is related to the progression of myopia, it seems reasonable that the reduction of the accommodative response through the use of plus reading glasses or through the use of bifocals on already myopic children should also have the effect of reducing the rate of progression of myopia in children. Such has been reported by a number of investigators (Betz, 1949; Gamble, 1949; Miles, 1957, 1962; Parker ?)
Studies referenced below have shown a small, but statistically significant decrease in progression of myopia in the first year of wearing the multifocals which remained similar and significant for the next 2 years.
Some authors have suggested that ( Optom Vis Sci. 2002 Oct;79(10):638-42) esophoria is a factor in slowing of myopia by progressive lenses and have investigated, finding there was only 46% as much myopia progression in the progressive lenses-esophoric group as in the progressive lenses-nonesophoric group. While multifocal lenses might not slow down or stop myopia progression in everyone with esophoria, it is a factor that should be taken into account on a case-by-case basis when analyzing methods of myopia control.
The COMET study: A randomized clinical trial of progressive addition lenses versus single vision lenses on the progression of myopia in children. (Investigative Ophthalmology and Visual Science. April 2003) was run with the purpose of evaluating the effect of progressive addition lenses (PALs) compared with single vision lenses (SVLs) on the progression of juvenile-onset myopia.
Mean 3-year increases in myopia (spherical equivalent) were −1.28 ± 0.06 D in the PAL group and −1.48 ± 0.06 D in the SVL group. The 3-year difference in progression of 0.20 ± 0.08 D between the two groups was statistically significant (P = 0.004). The treatment effect was observed primarily in the first year.
Use of PALs compared with SVLs slowed the progression of myopia in COMET children by a small, statistically significant amount only during the first year. The size of the treatment effect remained similar and significant for the next 2 years. The results provide some support for the COMET rationale—that is, a role for defocus in progression of myopia. The small magnitude of the effect does not warrant a change in clinical practice. . Gwiazda J, Hyman L, Hussein M, et al. A randomized clinical trial of progressive addition lenses versus single vision lenses on the progression of myopia in children. Invest Ophthalmol Vis Sci.2003;44:1492–1500. [PubMed]
Other studies have shown the correlation between multifocal lenses (bifocals and/or progressive addition lenses) to be stronger in the group of children that are “esophoric”, or have eyes that tend to rest inwards. This is also the population that tends to overfocus and exhibit pseudomyopia, which was discussed earlier. Fulk et al previously found after 30 months using bifocal lenses, the rate of myopia progression in 36 children wearing bifocals averaged 0.40 D/yr compared to 0.50 D/yr in 39 children wearing single-vision glasses (p= 0.046, age-adjusted). “Their follow up study, “A randomized clinical trial of bifocal glasses for myopic children with esophoria: results after 54 months” (Optometry. 2002 Aug;73(8):470-6) found Wearing bifocals instead of single-vision glasses caused a slowing of myopia progression evident during the first two years. During the subsequent two-and-a-half years of followup, the difference in the degree of myopia was maintained, but did not increase.
The Houston Myopia control study was the first randomized clinical trial designed to test the efficacy of bifocal lenses for the control of juvenile myopia. (Optom Vis Sci. 2000 Aug;77(8):395-401). Among the children completing the 30 months of follow up, myopia progression (mean spherical equivalent of the two eyes) averaged 0.99 D for bifocals and 1.24 D for single vision . They concluded use of bifocals, instead of single-vision glasses, by children with near-point esophoria seemed to slow myopia progression to a slight degree.
Their follow up study examined the pattern of change in myopia over the first and second halves of the 54-month period to see if the beneficial effect of wearing bifocals was present initially for those 46 children, as it was in the entire group, and to see if the myopia-slowing effect continued to accumulate during the second part of the study. found that the rate of progression tended to be the most rapid for subjects who entered the study at an early age with a large amount of myopia, and tended to be the least rapid for subjects who entered the study at a later age with a small amount of myopia. It was also found that subjects having with-the-rule astigmatism (astigmatism angled in a particular direction) progressed more slowly than those having no astigmatism or against-the-rule astigmatism.
Oakley et al, in their study “Bifocal Control of Myopia” performed a cross-cultural study that evaluated children in two age ranges; 6 to 8 year olds and 9 to 15 year olds. This study found a reduction in myopia averaging .48 diopters per year when comparing bifocal wearing children to single vision spectacle wearers. The implications of this study include for younger children, if referred for examination at age 8 with 1 diopter of myopia (-1.00 sph prescription) continuing to progress at the average rate for each year until 18 the child can be expected to develop approximately 5 diopters of myopia by the time he/she reaches 18 years of age. Based on this study, the ultimate prescription for the same child fit in bifocals during that time period in their life would fall between 0 and 1.40 D of myopia. (less than -1.50 sph prescription). The exceptionally low annual rate of change of -0.04 diopters per year found among bifocal subjects in this study is uncommon and suggests that the bifocals are having a controlling and reducing effect upon the rate of progression of myopia. The authors state that under reasonably well controlled conditions the bifocal appears to be effective in controlling the progression of myopia.
The Hong Kong Progressive Lens Myopia Control Study: Marion Hastings Edwards et al was structured to determine whether the use of progressive addition spectacle lenses reduced the progression of myopia over a 2 year period in Hong Kong children between the ages of 7 and 10.5 years. There were no statistically significant differences between the PAL and the SV groups for of any of the baseline outcome measures. After 2 years there had been statistically significant increases in myopia and axial length in both groups; however, there was no difference in the increases that occurred between the two groups. The research design used resulted in matched treatment and control groups. There was no evidence that progression of myopia was retarded by wearing progressive addition lenses, either in terms of refractive error or axial length. Edwards M, Li R, Lam C, Lew J, Yu B. The Hong Kong progressive lens myopia control study: study design and main findings. Invest Ophthalmol Vis Sci. 2002;43:2852–2858. [PubMed]