ELLASUVPRECISION OPTICS
Presbyopia & Accommodative Mechanics • 13 min read

Multifocal Contact Lens Optics: Concentric vs Aspheric Simultaneous Vision & MTF Metrics

EXECUTIVE CLINICAL SUMMARY
Simultaneous vision multifocal contact lenses project distant, intermediate, and near optical foci onto the fovea simultaneously, relying on cortical selective processing to isolate the sharpest image. By analyzing concentric ring versus continuous aspheric power profiles, pupil dynamics, and Modulation Transfer Function (MTF) degradation, clinicians can optimize presbyopic contact lens fitting.
ELLASUV Clinical Metrology Laboratory Ophthalmic Biomechanics & Accommodative Dynamics Division
ISO 8980-3 / ANSI Z80.1 Metrology • Updated: 2026-09-07 • ✓ Peer-Reviewed

The Simultaneous Vision Principle

Unlike translating/alternating bifocal contacts that physically shift upward with downward gaze, modern soft and GP multifocals utilize simultaneous vision. Distance and near wavefronts pass through the pupil aperture concurrently, casting simultaneous coaxial retinal images. The visual cortex attends to the focused target while ignoring the low-frequency defocused background halo.

Concentric Rings vs Continuous Aspheric Geometries

Simultaneous optics fall into two main surface topologies:

  1. Concentric Multi-Zone: Discrete alternating annular rings of distance and near powers. Delivers two sharp defocus peaks, but step transitions cause light scatter and halo flares around illuminated point sources.
  2. Continuous Aspheric (QQ-Value Modulation): Smooth progressive power change from center to periphery:
    • Center-Near: Takes advantage of pupillary miosis (2.0–2.5 mm2.0\text{--}2.5\ \text{mm}) during near convergence.
    • Center-Distance: Distance power centrally, adding near power peripherally. Preferred for outdoor sports and distance-dominant eyes.

Modulation Transfer Function (MTF) & Spherical Aberration

Because light is divided between focal planes, peak Modulation Transfer Function (MTF) at 30 cycles/degree30\ \text{cycles/degree} decreases from 0.650.65 in monofocal lenses to 0.25–0.350.25\text{--}0.35 in simultaneous multifocals.

By introducing negative spherical aberration (C40C_4^0), designers extend the depth of focus (EDOF) along the visual axis, creating continuous intermediate computer clarity (60–100 cm60\text{--}100\ \text{cm}) without sharp acuity cutoffs.

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FREQUENTLY ASKED CLINICAL QUESTIONS

Expert Answers

Why do multifocal contact lenses cause glare and halos at night? ▼
Because distance and near light rays enter the dilated pupil simultaneously. The light from the out-of-focus near power creates a diffuse, unfocused circular halo around illuminated point sources like vehicle headlights.
Can someone with high corneal astigmatism wear multifocal contact lenses? ▼
Yes, toric multifocal contact lenses exist. If corneal astigmatism exceeds -0.75 D, fitting a standard spherical multifocal will severely degrade optical MTF, as residual uncorrected astigmatism compounds the optical blur of the simultaneous power profile.
Why is pupillary illumination so critical when fitting multifocal contacts? ▼
Aspheric and concentric multifocal lenses rely on specific pupil zones. A patient with an abnormally small photopic pupil (e.g., 2.0 mm) wearing a center-distance lens will never access the peripheral reading add, rendering them unable to read.
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