ISO issues new standards for presbyopia-correcting IOL classification

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Historically, IOLs have been categorized in a number of ways: by optical technology (diffractive, refractive); by the number of foci (bifocal, trifocal); by add power (low or high add); and by purported mechanism of action (extended depth of focus [EDOF]). With today’s rapidly evolving landscape for IOL design, there is a need for IOLs to be better characterized according to their functional performance. Recently there have been several important advancements toward this goal.

New ISO standards

First, the International Organization for Standardization (ISO) issued new standards in early 2024. Last updated in 2018, ISO 11979-7 now defines an overarching category of simultaneous vision IOLs (SVIOLs), with 3 subcategories: multifocal IOL (MIOL), EDOF, and full visual range (FVR) IOLs. Clinical testing is required to document the achievement of the standards for each category, with the FVR category having the most stringent set
of requirements (Table^1,2). Clinical requirements include testing of mesopic contrast sensitivity, corrected distance visual acuity (VA), and distance-corrected intermediate and near VA.

This more contemporary construct characterizes IOLs by their performance rather than optical principles. For example, while the term trifocal clearly indicates 3 points of focus, it does not convey the extent to which the lens offers specific visual outcomes. In the past, a trifocal lens would undergo optical bench testing such as through-focus modulation transfer function and predicted defocus curves. That bench testing might or might not be made publicly available, but the lens would then be promoted as meeting certain image quality metrics. Under the ISO standards, any new lens would have to undergo clinical testing for at least 6 months (or 12 months if there is no approved monofocal of the same platform) to determine whether it meets visual acuity standards. Depending on which standards are met, a trifocal could be categorized as an MIOL or FVR IOL. The FVR IOL category describes the broadest range of vision. The first new FDA-approved IOL that meets the FVR standard was the TECNIS Odyssey IOL (Johnson and Johnson Surgical Vision). However, several other IOLs available in the US market, such as the enVista Envy (Bausch and Lomb), as shown in the examples in the Table, also fall into this category.

Global standardization for SVIOLs: A decade in the making

The ISO sets standards for a wide array of medical and consumer products, with the goal of facilitating international trade by ensuring equality, safety, and efficacy. Development of the rigorous ISO standard for SVIOLs is the culmination of 10 years of work by a global committee representing industry, clinicians, and regulatory agencies. Adoption of new standards is voluntary, but the new SVIOL standards have already been adopted by a number of countries, including the US and the European Union. To comply with the new standards, it is anticipated that IOL labeling will soon require a selection of the ISO standard clinical outcomes and a graph with a defocus curve.

The ISO also has toric lens standards. However, there is not yet an updated ISO standard for monofocal plus or enhanced monofocal IOLs, so the continuum from monofocal to EDF IOLs remains an opportunity for further clarification.

Professional society guidelines

In addition to the ISO standards, several profes­sional societies in ophthalmology have also weighed in on lens classifications. The European Society of Cataract and Refractive Surgeons (ESCRS) established the ESCRS Functional Vision Working Group, which published a proposed 6-category classification in which SVIOLs are subdivided into either partial or full range of field (ROF) in the defocus curve. Each of these 2 categories is further subdivided into functional classifications: narrow, enhanced, or extended partial ROF and continuous, smooth transition, or steep transition full ROF IOLs.¹

The full ROF lenses must have an ROF of at least 2.3 diopters (D) at 0.2 logMAR and at least 2.75 D at 0.3 logMAR. They are defined by the steepness of the increase in visual acuity from intermediate to near. The continuous category has an increase of less than 0.05 logMAR, the smooth transition category has an increase of at least 0.05 and less than 0.14 logMAR, and the steep transition category has an increase of at least 0.14 logMAR. A limitation of the ESCRS proposed criteria is that they do not account for dysphotopsia outcomes, which are also important for patient and clinician decision-making.

Separately, the ESCRS Functional Vision Working Group has also proposed that modified monofocal IOLs that do not fully meet the requirements to be considered EDOF lenses could be considered to be standard of care if there is enough scientific evidence to confirm their clinical superiority over conventional monofocal IOLs and the benefits justify the additional costs (if any).² The ESCRS committee is working in conjunction with a committee established by the American Society of Cataract and Refractive Surgery (ASCRS) to further refine IOL classifications on a functional basis. The ASCRS Functional Vision Group, chaired by Doug Koch, MD, comprises Vance Thompson, MD; Daniel Chang, MD; Kamran Riaz, MD; Nicole Fram, MD; Cathleen McCabe, MD; and me. This work is important. As the number of available IOLs has increased, lens choice and patient selection have become ever more complex. Updating classifications—both through the ISO and our professional societies—will help us to make better clinical decisions and further refine our decision-making process in IOL implant surgery.

References

1. Ribeiro F, Dick HB, Kohnen T, et al. Evidence-based functional classification of simultaneous vision intraocular lenses: seeking a global consensus by the ESCRS Functional Vision Working Group. J Cataract Refract Surg. 2024;50(8):794-798. doi:10.1097/j.jcrs.0000000000001502

2. Ribeiro F, Piñero DP, Dick HB, Findl O, Cochener B, Kohnen T. Should enhanced monofocal intraocular lenses be the standard of care? an evidence-based appraisal by the ESCRS Functional Vision Working Group. J Cataract Refract Surg. 2024;50(8):789-793. doi:10.1097/j.jcrs.0000000000001479