EDOF vs Multifocal IOL Testing: What Changes in Your QC Protocol and What Stays the Same

Introduction: You Know How to Test Multifocal. Now EDOF Is Coming to Your Line.

Your QC department has been testing multifocal IOLs for years. The protocol is validated. The operators are trained. The measurement systems are configured. The acceptance criteria are documented. The SPC charts are stable.

Then the product development team announces: the next premium IOL is EDOF, not multifocal. The VP asks whether the existing QC protocol covers it. The honest answer is: mostly. The more useful answer is: mostly, but the parts that differ are the parts that matter most.

Multifocal and EDOF IOLs share the same measurement infrastructure, the same regulatory framework, and many of the same quality parameters. But the optical mechanism that creates the premium performance is fundamentally different, and the QC protocol must reflect that difference. A multifocal QC protocol applied unchanged to an EDOF product will catch the standard power and MTF failures-and will systematically miss the EDOF-specific failure modes that determine whether the patient gets extended range of vision or an expensive monofocal.

This article is written for the QC manager who knows multifocal testing well and needs to understand exactly what changes for EDOF, what stays the same, and where the existing protocol needs specific modifications.

What Stays the Same: The Foundation You Already Have

Before detailing what changes, it is important to recognize that the majority of the QC infrastructure built for multifocal IOLs transfers directly to EDOF.

The measurement system

The same IOLA MFD that measures multifocal IOLs measures EDOF IOLs. The 9-second wavefront capture, the through-focus MTF computation, the Zernike decomposition, the power map, and the multi-aperture analysis all operate identically regardless of the IOL type. No hardware change is required. The system captures the complete wavefront and computes whatever optical metrics are needed for the specific lens type.

The regulatory framework

The ISO 11979-2 requirements for optical performance testing apply equally to multifocal and EDOF IOLs. Power measurement, MTF at best focus, model eye configuration, and documentation requirements are the same. The standard does not define separate testing categories for multifocal versus EDOF-both are premium presbyopia-correcting IOLs subject to the same regulatory framework.

Standard power and cylinder verification

Every IOL-monofocal, multifocal, or EDOF-must meet its labeled power within the ISO tolerance of ±0.30D (or tighter, depending on the manufacturer’s specification). Cylinder accuracy, axis alignment for toric designs, and optical center location are verified with the same protocols regardless of IOL type.

The model eye configuration

Both multifocal and EDOF IOLs are tested in a model eye per ISO 11979-2. The physical cornea, the measurement medium, and the conversion algorithms are the same for both lens types. The IOLA MFD’s interchangeable corneas (ISO Model Eyes 1 and 2, aspheric, spherical-aberration-free) serve both multifocal and EDOF testing.

Data infrastructure

The data export formats, the SPC software connections, the batch record systems, and the archival protocols built for multifocal transfer to EDOF without modification. The data types are the same (through-focus MTF, Zernike coefficients, power maps). What changes is how the data is interpreted and what acceptance thresholds are applied.

What Changes: The Six Specific Protocol Differences

The differences between multifocal and EDOF QC are specific, identifiable, and addressable. Each one reflects a fundamental optical difference between the two lens types.

Table 1: Multifocal vs EDOF QC Protocol – Side-by-Side Comparison

QC Dimension	Multifocal Protocol	EDOF Protocol	Why It Differs
Through-focus acceptance criterion	Discrete peak verification: MTF at far, intermediate, and near focal points must each exceed threshold (e.g., ≥0.43 at each designed focus)	Plateau verification: continuous MTF above threshold across a defocus range (e.g., ≥0.15 across 1.5D); width, minimum, and shape evaluated	Multifocal creates distinct focal peaks. EDOF creates a continuous range. Verifying peaks is different from verifying a plateau.
Through-focus curve shape expectation	Two or three discrete peaks separated by valleys. Valleys are expected and are part of the design (light energy splits between foci).	Smooth continuous plateau with no valleys. Any valley or dip within the designed range indicates a defect, not a design feature.	In multifocal, a valley is designed. In EDOF, a valley is a defect. The same observation has opposite interpretations.
Add power verification	Essential: the difference between far and near peaks defines the add power. Must match labeled add (±0.25D to ±0.50D depending on spec).	Not applicable: EDOF has no discrete near focal point. There is no “add power” to verify. Attempting to measure it returns meaningless values.	EDOF extends range continuously, not through a defined near addition. The concept of add power does not apply.
Diffractive order efficiency (for diffractive designs)	Critical: the energy split between zeroth and first (and sometimes second) diffractive orders determines the far/near ratio. Must verify energy balance.	Different: diffractive EDOF designs use echelette structures that modify the through-focus profile without creating discrete orders. Energy is distributed across a range, not split between peaks.	Multifocal diffractive: energy split into discrete orders. EDOF diffractive: energy distributed across a continuous range. Verification methods differ.
Pupil dependency assessment	Moderate importance: multifocal designs typically maintain discrete peaks at all pupil sizes (the energy ratio shifts but peaks persist).	Critical importance: refractive EDOF plateau can collapse at larger pupils. Must verify at 3mm AND 4.5mm. Plateau narrowing >40% is a significant finding.	Multifocal peaks persist across apertures. EDOF plateau depends on the central modification zone, which is diluted by peripheral lens at larger pupils.
SA coefficient monitoring	Not typically monitored: multifocal designs do not rely on specific SA profiles. Aberration control is important but not the primary design mechanism.	Essential for wavefront-shaping EDOF: Z₄⁰, Z₆⁰, and their ratio define the plateau. SA coefficient SPC is the leading indicator of EDOF performance drift.	EDOF uses SA as the optical mechanism. Monitoring SA is monitoring the design itself. Multifocal uses diffraction or refractive zones, not SA tuning.
Dysphotopsia assessment	High priority: multifocal designs inherently produce halos and glare from diffractive light splitting. Halo energy measurement or PSF evaluation may be part of QC.	Lower priority for refractive EDOF: wavefront-shaping designs produce less halo than diffractive multifocals. PSF evaluation may still be relevant for diffractive EDOF designs.	Different light distribution mechanisms produce different dysphotopsia profiles. QC priority reflects clinical significance for each design type.

Difference 1: Peaks vs Plateau – The Fundamental Shift in Through-Focus Thinking

This is the single most important conceptual change for the QC manager transitioning from multifocal to EDOF.

A multifocal IOL splits light energy into two or three discrete focal points. The through-focus MTF curve shows distinct peaks at the far, intermediate, and near focal distances. QC verification confirms that each peak exceeds the minimum MTF threshold and that the peaks are located at the correct defocus positions (matching the labeled add power).

An EDOF IOL distributes light energy across a continuous range. The through-focus MTF curve shows a plateau-a sustained region of acceptable contrast without distinct peaks or valleys. QC verification confirms that the plateau is present, is wide enough, maintains minimum MTF throughout, is centered at the correct defocus position, and is consistent across aperture sizes.

The consequences for QC interpretation are immediate. On a multifocal through-focus curve, a valley between the far and near peaks is normal-it is the designed gap between focal points. On an EDOF through-focus curve, any valley within the designed range is a defect-it indicates a disruption in the continuous range of vision that the patient expects.

A QC operator trained on multifocal curves who encounters a dip in an EDOF through-focus curve may instinctively accept it as “normal between-peak behavior.” This misinterpretation passes a defective EDOF lens. The through-focus interpretation framework specific to EDOF plateau evaluation provides the pattern recognition training needed to avoid this error.

Difference 2: No Add Power – The Parameter That Disappears

Every multifocal QC protocol includes add power verification: the measured difference between the far focus and the near focus, typically expressed in diopters. The labeled add power (+2.75D, +3.25D, etc.) must match the measured add within tolerance. This is a critical acceptance criterion because the add power determines the patient’s near vision capability.

EDOF IOLs have no add power. There is no discrete near focal point. The extended range is continuous, not stepped. Attempting to measure “add power” on an EDOF lens produces a number that represents the distance between the peak of the plateau and an arbitrary threshold point-not a clinically meaningful near focus.

For the QC protocol, this means removing the add power verification step from the EDOF acceptance criteria. It is not relaxed or modified-it is eliminated. In its place, the EDOF protocol substitutes plateau width verification: the defocus range over which MTF remains above the defined threshold. This plateau width is the EDOF equivalent of the multifocal add power-it describes the functional range of vision, just measured differently.

The practical implication: if the measurement system’s product configuration for multifocal includes an automatic “add power” calculation, this calculation must be disabled or replaced for EDOF product codes. Leaving it active will generate a spurious “add power” number that operators may attempt to evaluate against multifocal criteria, leading to incorrect pass/fail decisions.

Difference 3: Pupil Dependency Becomes Critical

Multifocal IOLs, particularly diffractive designs, maintain their multiple focal points across a range of pupil sizes. The energy ratio between distance and near shifts with pupil size (apodized designs intentionally shift toward distance at larger pupils), but the discrete focal peaks persist. A multifocal IOL that provides a clear near focus at 3mm generally still provides a near focus at 4.5mm, even if at reduced energy.

Refractive EDOF IOLs behave differently. The surface modification that creates the extended range is concentrated in the central zone-typically 2.0–2.5mm diameter. At a 3mm pupil, this modification zone fills most of the aperture. At a 4.5mm pupil, the unmodified peripheral lens contributes significantly to the image. The peripheral contribution acts as a monofocal component that dilutes the EDOF effect.

The practical consequence: an EDOF lens that shows a wide, well-defined plateau at 3mm may show a narrower or even collapsed plateau at 4.5mm. A multifocal lens tested only at 3mm will still deliver its near focus at larger pupils. An EDOF lens tested only at 3mm may not deliver its extended range at larger pupils.

For the QC protocol, this means mandatory verification at two aperture sizes for EDOF: the ISO-standard aperture (typically 3mm) and a larger aperture representing mesopic conditions (4.5mm). The IOLA MFD computes multi-aperture through-focus from a single wavefront capture-no additional measurement time required. For multifocal, multi-aperture verification is useful but not critical. For EDOF, it is essential.

Difference 4: SA Monitoring Enters the QC Vocabulary

Multifocal QC managers rarely think about spherical aberration coefficients. The diffractive ring structure or the refractive zone geometry creates the multiple foci through physical features that are verified by the through-focus MTF-not by aberration analysis. SA is a secondary parameter that affects image quality but does not define the multifocal mechanism.

For wavefront-shaping EDOF, SA is the mechanism. The controlled introduction of Z₄⁰ and Z₆⁰ is what creates the extended range. If Z₄⁰ drifts by 15%, the plateau narrows. If Z₆⁰ under-delivers by 20%, the plateau shape degrades. If the Z₄⁰/Z₆⁰ ratio shifts, the through-focus profile changes character even if the plateau width measurement still passes.

The QC protocol addition: Zernike coefficient monitoring for EDOF. This is implemented as Tier 2 diagnostic SPC charts that the QC manager reviews when the primary through-focus charts signal an issue. The SA coefficients are not pass/fail criteria for individual lenses (the through-focus plateau is the functional acceptance criterion), but they are the leading indicators that predict through-focus drift before it reaches the rejection threshold.

For the QC manager who has never worked with Zernike coefficients and wavefront data in a production context, this is the steepest learning curve in the multifocal-to-EDOF transition. The good news: the measurement system generates the coefficients automatically. The interpretation framework-which coefficient maps to which manufacturing parameter-is the knowledge that must be acquired.

Difference 5: The Failure Mode Landscape Changes

Multifocal and EDOF IOLs share some failure modes (power error, cylinder error, decentration) and have others that are unique to each design type.

Table 2: Failure Mode Comparison – Multifocal vs EDOF

Failure Mode	Multifocal Impact	EDOF Impact	QC Detection Method
Power error (±0.3D)	All focal peaks shift equally. Distance and near both defocused.	Entire plateau shifts on defocus axis. Distance and intermediate both affected.	Standard power measurement. Same for both.
Surface decentration (coma)	Far and near peaks degraded symmetrically. MTF reduced at all foci.	Plateau asymmetry: one side degrades preferentially. Intermediate vision affected directionally.	Through-focus at two apertures. EDOF shows asymmetric effect not visible in multifocal.
Diffractive ring spacing error	Near peak shifts or splits. Add power deviates from label.	Not applicable (refractive EDOF) or modified echelette profile changes (diffractive EDOF).	Multifocal: add power measurement. Diffractive EDOF: through-focus profile shape.
Aspheric profile error (SA deviation)	Minor effect on image quality. Peaks remain; contrast slightly reduced.	Major effect: plateau width and shape change directly. The SA profile IS the EDOF mechanism.	Multifocal: through-focus MTF. EDOF: SA coefficient monitoring + through-focus.
Surface roughness (mid-spatial frequency)	Increased scatter; halo energy increases. MTF at all foci reduced.	Increased scatter within plateau; minimum MTF within range drops. More damaging to EDOF because the plateau is already lower than multifocal peaks.	Through-frequency MTF at 50 lp/mm. EDOF more sensitive because starting MTF is lower.
Z₄⁰/Z₆⁰ ratio drift	Not applicable: multifocal does not rely on SA ratio.	Plateau shape changes: becomes asymmetric, narrower, or shifted even when individual SA terms are within limits.	EDOF-only: SA ratio SPC chart. No multifocal equivalent.
Plateau collapse at large pupil	Not applicable: multifocal peaks persist at all pupils.	Extended range lost at mesopic conditions. Patient reports poor intermediate in dim lighting.	EDOF-only: mandatory multi-aperture verification. Not required for multifocal.

What to Change in Your Protocol: The Practical Checklist

For the QC manager adapting an existing multifocal protocol for EDOF, the following specific changes are required. Each change is localized-it modifies a specific section of the existing protocol rather than requiring a rewrite.

1. Acceptance criteria document: Replace the discrete peak MTF thresholds (far, intermediate, near) with plateau width and minimum MTF within range thresholds. Remove the add power criterion. Add plateau center position criterion. Add multi-aperture verification at 4.5mm.
2. Measurement system configuration: Create new product codes for each EDOF product that include the EDOF-specific acceptance criteria. Disable the automatic add power calculation. Enable through-focus plateau analysis mode (plateau width, center, minimum). Ensure multi-aperture computation is active.
3. Operator training: Add through-focus plateau interpretation module (2 hours). The critical training point: valleys between peaks are normal on multifocal-valleys within the plateau on EDOF are defects. Retrain disposition logic: four outcomes instead of binary pass/fail.
4. SPC charts: Add plateau width X-bar/R chart (Tier 1). Add minimum MTF within range chart (Tier 1). Add SA coefficient I-MR charts (Tier 2 diagnostic). Add Z₄⁰/Z₆⁰ ratio chart (Tier 2 diagnostic, EDOF-only).
5. Investigation procedures: Add the SA coefficient diagnostic pathway to the root cause analysis SOP. When a through-focus failure occurs, the investigation now includes: check Z₄⁰, check Z₆⁰, check Z₄⁰/Z₆⁰ ratio, check total parasitic RMS. This is in addition to the standard checks (power, decentration, surface quality).
6. Reference lens inventory: Add EDOF reference lenses for system verification. A multifocal reference lens verifies that the system measures discrete peaks correctly. It does not verify that the system computes plateau metrics correctly. EDOF verification requires EDOF references.

What Not to Change: Avoiding the Over-Reaction

The transition from multifocal to EDOF QC sometimes triggers an over-reaction: the QC manager decides to rebuild the entire protocol from scratch. This is unnecessary and counterproductive. The following elements should remain unchanged.

Do not change the measurement hardware. The same IOLA MFD that measures multifocals measures EDOF. Do not change the model eye configuration unless the EDOF design specifically requires a different cornea model (verify with the R&D team). Do not change the data export format or the SPC software. Do not change the batch record structure-add EDOF-specific fields, but keep the existing structure.

Do not create a separate QC station for EDOF. The same instrument, the same operator, and the same station handle both product types. The protocol difference is in the software configuration (product code → acceptance criteria) and in the operator’s interpretive framework, not in the physical infrastructure.

Do not over-complicate the operator’s role. The operator’s job is still: load the lens, press measure, review results, disposition the lens. The system computes the through-focus parameters automatically. The operator compares results to thresholds. What changes is which thresholds are applied and what the through-focus display looks like-not the fundamental workflow.

Conclusion

The transition from multifocal to EDOF QC is not a protocol replacement-it is a protocol adaptation. The measurement system stays. The regulatory framework stays. The power verification stays. The model eye stays. The data infrastructure stays.

What changes is the through-focus acceptance logic (plateau, not peaks), the loss of the add power criterion (replaced by plateau width), the addition of mandatory multi-aperture verification, the introduction of SA coefficient monitoring as a leading indicator, and the operator’s interpretive framework (valleys are defects, not features).

For the QC manager who already runs multifocal testing successfully, the EDOF adaptation requires six specific changes to the existing protocol, an updated training module of approximately 2 hours for operators, and new EDOF reference lenses for system verification. The measurement itself takes the same 9 seconds. The system that generates the data is the same system. The change is in what you look at and what you expect to see.

A multifocal through-focus curve has peaks and valleys. An EDOF through-focus curve has a plateau and nothing else. The QC protocol for each must match what the design intends. The manager who understands this difference in one sentence understands 80% of the protocol adaptation. The remaining 20% is implementation detail-and this article provides it.

Disclaimer: This document is intended for educational use only. It does not represent legal, regulatory, or certification advice, and should not be interpreted as a declaration of compliance or approval by Rotlex or any regulatory authority.