July 2, 2019
By Karen Lahav-Yacouel
PhD Student – Brien Holden Vision Institute
Myopia is on the rise globally. Research on ways to minimise the progression of myopia is growing in interest with many varied strategies including optical, pharmaceutical and environmental. There is evidence that myopia progression can be controlled optically, specifically with lenses that have been designed to impose myopic defocus on the periphery. Such lenses are multifocal in nature and may reduce visual performance and subjective acceptability, thus making the quality of vision important to assess. This article (Kang et al. 2017) reports the analysis of commercially available low and high add multifocal soft contact lenses (MF SCLs) prescribed for myopia control and their effect on quality of vision in young myopic adults.
The two MF SCLs assessed were the Proclear centre distance CL with +1.50 D (MF 1.5) and +3.00 D (MF 3) add powers, with Proclear spherical, single vision (SV) contact lenses (CLs) used as a reference. Each style of lens was worn by 24 adult participants for two weeks, with a one-week washout period. Quality of vision, high- and low-(50 percent)-contrast visual acuity (VA) and a Quality of Vision (QoV) questionnaire were assessed at the fitting visit and at the end of the two-week wear.
Results indicated that both MF SCLs reduced the high and low contrast VA relative to the SV lens. Vision with the MF 1.5 was not significantly different to the SV lens at both insertion and after two weeks (reduced by few letters only). The high and low-contrast VA with MF 3 were significantly reduced after insertion (<1 line as interpreted from Figure 3) and did not significantly change over the two-week period. With MF 3, high-contrast VA improved by few letters after two weeks of lens wear, whereas the low-contrast VA further deteriorated.
Questionnaire scores relative to SV were worse for both MF SCLs. At the initial fitting visit, there were no significant differences between MF 1.5 and SV, but significant increased symptoms were reported two weeks later. For MF 3, reduced quality of vision was reported at the fitting visit and reduced further two weeks later. Thus, in terms of visual symptoms, neither lens displayed an adaptation over the two weeks of lens wear.
The current study draws attention to the disparity between the measured VA and the quality of vision as reported by symptoms. For MF 1.5, high- and low-contrast VA appear to be less sensitive measures of quality of vision, as neither exhibited significant change whereas the symptoms significantly worsened after two weeks. For the MF 3 lens, the low-contrast VA did parallel the vision quality results, both worsening after two weeks, while the high-contrast VA slightly improved. These observations therefore suggest that high-contrast VA is not a suitable indicator of quality of vision, whereas low-contrast VA may be more indicative. The researchers suggest that practitioners using these lenses for myopia control must be aware of this and educate their patients appropriately.
Authors and publication: Kang P, McAlinden C and Wildsoet C. Acta Ophthalmologica, 2017.
To assess the effects of multifocal soft contact lenses (MF SCLs) used for myopia control on visual acuity (VA) and subjective quality of vision.
Twenty-four young adult myopes had baseline high- and low-contrast VAs and refractions measured, and the quality of vision was assessed by the Quality of Vision (QoV) questionnaire with single vision SCLs. Additional VA and QoV questionnaire data were collected immediately after subjects were fitted with Proclear MF SCLs and again after a two-week adaptation period of daily lens wear. Data were collected for two MF SCL designs, incorporating +1.50D and +3.00D peripheral near additions, with a one-week washout period allowed between the two lens trials.
High- and low-contrast VAs were initially reduced with both MF SCL designs, but subsequently improved to be not significantly reduced in the case of high-contrast VA by the end of the two-week adaptation period. The quality of vision was also reduced, more so with the +3.00D MF SCL. QoV scores describing frequency, severity and bothersome nature of visual symptoms indicated symptoms worsening rather than resolving over the two-week period, particularly so with the +3.00D MF SCL.
Low- and high-add MF SCLs adversely affected vision on initial insertion, with sustained effects on low-contrast VA and QoV scores but not on high-contrast VA. Thus, high-contrast VA is not a suitable surrogate for quality of vision. In prescribing MF SCLs for myopia control, clinicians should educate patients about these effects on vision.