New research published in Ophthalmic & Physiological Optics measured the refractive power profiles of various multifocal soft contact lenses (MFCLs) that have the potential to or are currently utilized in myopia control to determine their power profiles.
Give me some background first.
Various interventions are available to mitigate or stop the progression of myopia, including:
- Pharmacological
- Light-based treatments
- Optical treatments
In this case: MFCLs fall under the category of optical treatments, with their primary goal being to prevent the excessive axial elongation underlying myopia progression.
Now, talk about the study.
Researchers measured the power profiles of 10 MFCLs of various designs with the Lambda-X NIMOEVO—a phase-shifting Schlieren-based device. These profiles were filtered into three categories:
- Center-distance
- Center-near
- Extended depth-of-focus (EDOF) lenses
Note: Schlieren imaging is an optical technology that photographs the flow of liquids of varying density.
Also: The investigators noted that most MCFLs for myopia control are either center-distance or EDOF designs.
Why focus on power profiles?
The investigators said it best: “Understanding power profiles provides important insights as to how MFCL parameters may influence retinal defocus and the visual experience”—both of which are important factors for future MFCL development, they noted.
Gotcha. Back to this study: Then what did they do?
The investigators then graphically expressed power profiles as measured power at each chord position before calculating maximum add power.
From there, they expressed the repeatability of the NIMO device as the within-subject standard deviation at each chord position for a subset of five MFCLs:
Center-distance
- Acuvue Oasys for Presbyopia
- MiSight 1-Day
Center-near
- PureVision2 for Presbyopia
- 1-Day Acuvue Moist
EDOF
- SEED 1dayPure EDOF
Which MFCLs were evaluated?
- MiSight 1-Day (CooperVision)
- Biofinity MultiFocal (MF) (CooperVision)
- Proclear MF (CooperVision)
- 1-Day Acuvue Moist MF (Johnson & Johnson Vision Care; JJVC)
- Acuvue Oasys for Presbyopia (JJVC)
- PureVision2 for Presbyopia (Bausch + Lomb)
- SEED 1dayPure EDOF (SEED CO. Ltd)
- NaturalVue MF 1-Day (VTI Vision)
Findings?
The investigators determined that:
- Measured distance powers differed from nominal powers for more than half of the MFCLs with a definable distance zone
- The repeatability of the NIMO device was dependent on the lens design
- Designs that featured faster rates of power change exhibited worse repeatability
- For half of MFCLs: The power profile shape was inconsistent between different nominal back vertex powers of the same design
Any variations noted?
Yes! Specifically in:
- Chord position of the distance and near correction zones
- Rate of power transitions
- Calculated maximum add between the MFCLs (which were not dependent on lens design)
So what led to these labeling inconsistencies?
The investigators noted that the labeling inconsistencies may be due to the inherent challenges associated with categorizing lens designs using predefined parameters.
Limitations?
Distance and ad powers frequently deviated from the nominal lens power, differences the researchers could not predict based on lens type or labeling.
The authors also noted that a majority of the lens types demonstrated increased minus power in the periphery with increasing BVP, which could have had implications for providing consistent defocus between individuals with varying degrees of myopia.
What else?
Additionally, the study utilized default central smoothing filters which may have resulted in the slight masking of the central power profile.
Lastly, only specific back vertex powers (BVPs) and additions (adds) were considered in the study due to the limited power range or availability of certain MFCLs included in their analysis.
Expert opinion?
The authors recommended that eyecare practitioners “should be aware of potential differences in power profiles between different MFCLs” due to the impact on their retinal defocus and overall visual experience.
They further noted that the MFCL lens power profiles were neither consistent or accurately represented by their labeling.
Take home.
The study found that there were significant differences in MFCL profiles that were not adequately represented in labeling.