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What Defocus Curves Actually Tell You About Near, Intermediate, and Distance Performance

1 min read

A defocus curve is the single most informative chart in premium IOL planning, and the most commonly misrepresented in marketing materials. Understanding what it shows, and what it does not, separates real comparison from manufacturer storytelling.

What a Defocus Curve Measures

A defocus curve plots visual acuity against simulated refractive error, typically from +1.0 D through 0 D (distance) to −3.0 D or beyond (near). The shape reveals where each lens delivers usable vision, where it does not, and how steeply performance drops off between focal points.¹

What It Shows for Each Lens

A monofocal lens produces a sharp single peak at distance with a steep fall-off. A monofocal-plus lens widens the peak slightly. An EDOF lens produces a broader plateau extending into intermediate. A trifocal lens produces three discrete peaks corresponding to distance, intermediate, and near.²

The Misuse

Manufacturer comparisons frequently average data across patients with optimised refractive outcomes, healthy ocular surfaces, and select pupil sizes. Real-world defocus curves are noisier, with greater variance between individuals.³ Two patients with the same trifocal lens implanted by the same surgeon can produce visibly different defocus curves on the same day.

What Patients Should Ask

Whether a published defocus curve represents the patient population the patient resembles, whether the testing pupil and lighting conditions match the patient’s life, and whether the curve reports binocular or monocular performance. Binocular curves overstate near performance compared with monocular reality.

The Clinical Position

A defocus curve is a useful pedagogical tool. It is not a guarantee. The curve tells you what is possible. The eye, the brain, and the system around the surgery determine what is delivered.

References

  1. Buckhurst PJ, Wolffsohn JS, Naroo SA, Davies LN, Bhogal GK, Kipioti A, Shah S. Multifocal intraocular lens differentiation using defocus curves. Invest Ophthalmol Vis Sci. 2012;53(7):3920-3926.
  2. Böhm M, Petermann K, Hemkeppler E, Kohnen T. Defocus curves of 4 presbyopia-correcting IOL designs: diffractive panfocal, diffractive trifocal, segmental refractive, and extended-depth-of-focus. J Cataract Refract Surg. 2019;45(11):1625-1636.
  3. Kohnen T, Böhm M, Hemkeppler E, Schönbrunn S, DeLorenzo N, Petermann K, Herzog M. Visual performance of an extended depth of focus intraocular lens for treatment selection. Eye (Lond). 2019;33(10):1556-1563.

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About Blue Fin Vision®

Blue Fin Vision® is a GMC-registered, consultant-led ophthalmology clinic with CQC-regulated facilities across London, Hertfordshire, and Essex. Patient outcomes are independently audited by the National Ophthalmology Database, confirming exceptionally low complication rates.