Enhancing the depth of focus in cataract surgery

At the completion of this article, the reader should…

•  Understand the role of extended depth of focus (EDOF) intraocular lenses (IOLs) in modern cataract surgery.

•  Differentiate between monofocal, multifocal, and EDOF IOL designs and their impact on patient outcomes.

•  Apply clinical insights when counselling patients pre-surgically on refractive options and expected outcomes.

Dr Graham Hay-Smith
MA(Oxon), MA, ACFA(UK), MBBS,
MRCS(Ed), FRCOphth, FRANZCO
The Moreton Eye Group
Brisbane, Queensland

As the baby boomer generation ages cataract surgeries are on the rise. And these patients now expect more than restored sight — they want vision that supports their daily life. Dr Graham Hay-Smith says optometrists play a key role in this process, guiding realistic expectations, ensuring informed referrals, and supporting their patients’ adaptation to modern EDOF technologies.

Cataract surgery has evolved from a high-risk intervention to restore sight into a routine, yet transformative procedure that delivers excellent unaided vision in the aging eye. Aphakic spectacles, ubiquitous when I started my ophthalmology career, are now museum curiosities. Today, achieving 6/6 unaided vision is the expectation, and presbyopia management is a routine discussion in the surgeon’s clinic.

Ideally, this discussion should begin with the referring optometrist, many of whom have managed the patient for years. Often the optometrist is much more familiar with their patients’ lifestyle, personality, and visual demands. This insight is valuable when optimising the lens choice.

The aim of this article is to encourage optometrists to engage fully in the refractive outcomes of their patients’ cataract journey from the outset. The focus is on newer intraocular lenses (IOLs) designed to extend the range of vision – primarily in the context of monovision strategies – with the goal of reducing spectacle dependence (multifocal IOLs have been extensively discussed elsewhere and lenses not included on the Australian Prosthesis List are beyond the scope of this review).

The sheer variety of new lens platforms designed to extend the depth of focus, each with distinct optical properties and performance claims, reflects both the clinical utility and their rising popularity worldwide.

In response, manufacturers have introduced a variety of solutions to address a familiar challenge: how to optimise visual outcomes and patient satisfaction.

Monovision as an option

Monovision predates multifocal IOLs and remains a versatile and well-established strategy. By targeting emmetropia in one eye and mild myopia in the fellow eye, patients can achieve an extended range of functional vision and reduce reliance on spectacles for near tasks and still achieve excellent distance vision without dysphotopsias.

In my practice, I use monovision instead of multifocals more often than in the past, for two principal reasons:

1. Changing visual demands: intermediate vision (50–150 cm) is now more important than traditional near vision (20-50 cm). Thirty years ago, vision was judged by clarity at distance and the ability to read print at 25-30 cm. Daily life now demands clarity at arm’s length – for smartphones, tablets, computer screens, and modern car displays. A patient who can comfortably read N6 at 50 cm and use digital devices is usually highly satisfied.

2. Advances in IOL technology: contemporary IOLs are now available that extend the depth of focus, enabling blended monovision strategies with fewer compromises than in the past.

Monovision and extended range of vision

Available IOL options that complement monovision strategies include:

• Diffractive EDOF lenses – weak diffractive platforms such as the Symfony (Abbott/Johnson & Johnson) have been part of the armamentarium now for a decade. They provide a proven extended depth of focus with fewer dysphotopsias than full multifocals.

• Refractive EDOF lenses – designs such as the Lentis MF150 use low refractive adds to extend vision but inherently produce some blur due to simultaneous foci. They are often well tolerated and are a well-established option providing well over a dioptre of focal range.

• Small-aperture lenses – like the IC-8 (Bausch + Lomb) are a true EDOF and are useful in selected cases but are not a mainstream option in my practice due to the loss of mesopic and scotopic performance.

• Spherical aberration-based designs – the newest EDOF/’enhanced monovision’ (RayOne EMV, Rayner) lenses leverage spherical aberration to increase depth of focus. These fall into three categories:

1. Negative aberration and presumed negative (proprietary) aberration (e.g. Vivity, Alcon) and (Eyhance, J&J).

2.Positive spherical aberration designs (e.g. RayOne EMV, Rayner)

3.Mixed and higher order aberration (e.g. Luxsmart, Bausch + Lomb)

For clarity, I will use the umbrella term ‘extended depth of focus (EDOF)’ to describe this family, acknowledging its limitations.

EDOF definition for this article

EDOF IOLs are designed not to split light but to stretch the point spread function (PSF) along the optical axis, producing a continuous range of focus. Strictly speaking, this is not a ‘depth of focus,’ but as that is the term commonly used, I will stick with it. The result is not perfect clarity at every distance but good enough retinal image quality across a broader range of vergences.

This is reflected in the modulation transfer function (MTF) curve:

• Monofocals produce a single tall, narrow peak.

• Multifocals produce multiple peaks with dips in between.

• EDOF lenses show a single elongated plateau, sacrificing peak sharpness for extended usable range.

In the human optical system, good vision is not just optics but a complex physiological process which has evolved over aeons.

Role of spherical aberration

Spherical aberration (SA) refers to the difference in refraction between peripheral and central light rays. In a lens with positive SA, the peripheral rays are refracted more strongly than paracentral rays; negative SA occurs when they are refracted less. The cornea of cataract-age patients naturally has positive SA, the average is around 0.27um. Both positive and negative SA have the effect of extending the depth of focus, at the theoretical expense of maximum contrast (Figure 1).¹

When positive SA is employed, peripheral light is refracted more strongly. This moves the point of focus of the periphery towards myopia. This is advantageous in mesopic and scotopic situations when the pupillary aperture is larger. In photopic conditions, with a small pupil, the pinhole effect provides enhanced depth of field. It appears logical to use a lens which has optics that intrinsically favours myopia in low light over hypermetropia.

Aspheric IOLs with negative SA were introduced over 20 years ago to correct the cornea’s natural positive SA (Figure 2). The rationale was to compensate for the positive SA in the cornea and to improve contrast and night vision. However, evidence supporting the routine correction of physiological SA is mixed with many studies showing little to no effect on CDVA and other metrics.^2,3 Some studies do show slightly improved contrast sensitivity, but at the expense of depth of focus.⁴

Recently, leading figures such as Professor Graham Barrett have explored the potential benefits of carefully controlled positive SA.⁵ The RayOne EMV lens cleverly adds the positive SA in the central region of the lens, it then gradually reduces it at the periphery. In this way, depth of focus can be increased without significant loss of contrast in low light. His RayOne EMV lens intentionally augments the natural positive aberration of the human cornea to increase perceived depth of focus at the retina (Figure 3).^5,6

Practically speaking, positive SA is preferable to negative SA because the ’spread energy’ (the area under the MTF curve) shifts more toward myopia, which is functionally useful, rather than hyperopia (Figure 4).

My own experience with RayOne EMV lenses, frequently combined with planned monovision, has been positive, usually yielding a functional range of vision with minimal subjective compromise. The trade-off (and there must always be a trade off as physics cannot be cheated) is mild blur in the myopic eye, which, because it is mild, tends to be very well tolerated.

The goal is to keep the blur within the tolerance of the human visual system – which, unlike the Hubble telescope, evolved to accept and interpret imperfections. Binocular summation further enhances perception, allowing mild blur to be integrated into a highly satisfactory visual experience. When employing monovision with RayOne EMV lenses, due to the extended depth of focus in both a myopic and hyperopic direction, there is a greater blended vision zone and less anisometropia than with standard monovision. Smaller anisometropic differences also minimises compromise to stereopsis. This results in much better acceptance of the strategy by the patient (Figure 5).

Strategies and counselling

When discussing lens options, I outline three broad strategies to my patients:

1. The ‘KISS’ principle (bilateral emmetropia) – monofocal lenses targeted for distance provide the sharpest distance acuity, with spectacles required for near/intermediate tasks. This remains the choice of many ophthalmologists for themselves.

2. Multifocal IOLs – clinical trials and experience demonstrate that multifocal IOLs can provide a high level of spectacle independence. However, inherent trade-offs include glare, halos, and reduced contrast sensitivity, with best outcomes achieved in eyes free of comorbidity. In a trial of unselected patients, one in 20 patients struggled with dysphotopsia to the point of requesting a lens exchange.⁷ Up to one in five can experience troublesome night-time visual phenomena.⁷ Most surgeons avoid implanting these lenses in patients with high night-vision demands, such as regular night drivers. With appropriate patient selection and thorough counselling, most individuals adapt well and achieve satisfactory outcomes.

3. Monovision – a flexible strategy, which is usually well tolerated, even more so with IOLs designed for this approach. Patients benefit from enhanced intermediate function with limited optical side effects. My usual target is -0.75 D to -1.0 D in the near eye, this will yield a near acuity of around 1.7 5D to 2.0 D, often translating to N5 or N6 BEO vision. Nearly all patients fall into 0.5 D to 2.0 D range depending on patient preference. Monovision has the great advantage that augmentation with spectacle correction remains efficacious, for example if night driving or fine reading tasks are not satisfactory.

The optometrist’s role

Patient education is essential. It is much more effective if it begins before the surgical consultation. Optometrists are ideally placed to initiate these discussions, drawing on their long-standing knowledge of the patient’s lifestyle and preferences.

Examples:

• A history of successful monovision contact lens wear strongly suggests suitability for surgical monovision.

• A phoria or binocular instability may make monovision and multifocals inappropriate.

• Passion for night-sky observation or working as a pilot or similar may rule out multifocals.

Optometrists can also guide realistic expectations and ensure relevant information is included in the referral. Post-operatively, they play a vital role in supporting adaptation to the strategy chosen (e.g. reassuring multifocal patients during neuroadaptation, prescribing task-specific spectacles for monovision patients).

Special considerations

• Poor corneal quality or irregular astigmatism.
– Best managed with aspheric-neutral monofocal lenses (e.g. Rayner RayOne). Multifocals should be avoided. Potentially small aperture lenses in certain patients.

• Compromised retina (AMD, glaucoma, diabetic retinopathy).
– Patients may benefit most from simple lens strategies and spectacle correction, rather than advanced IOLs.

• Strabismus, tropias and amblyopia.
– These patients do best with a simple emmetropic correction in my opinion.

• Abnormal pupils.
– Small pupils limit access to multifocal diffractive zones, while large pupils exacerbate dysphotopsia and can induce hyperopic or myopic shifts with some EDOF designs. RayOne EMV, with positive SA, are more forgiving in these cases.

Conclusion

The expansion of EDOF technologies has reshaped the landscape of refractive cataract surgery. For many patients, enhanced monovision with modern lenses, like RayOne EMV, provides a great balance of range, quality, and tolerance unmatched by earlier designs.

Ultimately, outcomes depend not only on lens choice but on individualised counselling, optometrist collaboration, and realistic expectation setting. 

References:

1. Rocha KM, Vabre L, Chateau N, Krueger RR. Expanding depth of focus by modifying higher-order aberrations induced by an adaptive optics visual simulator. J Cataract Refract Surg. 2009 Nov;35(11):1885-92. doi:10.1016/j.jcrs.2009.05.059. PMID: 19878820.
2. Al-Sayyari TM, Fawzy SM, Al-Saleh AA. Corneal spherical aberration and its impact on choosing an intraocular lens for cataract surgery. Saudi J Ophthalmol. 2014;28(4):274-80. doi:10.1016/j.sjopt.2014.06.007.
3. Nanavaty MA, Spalton DJ, Gala KB. Fellow-eye comparison of 2 aspheric microincision intraocular lenses and effect of asphericity on visual performance. J Cataract Refract Surg. 2012 Apr;38(4):625-32. doi: 10.1016/j.jcrs.2011.10.039. Epub 2012 Feb 18. PMID: 22342007
4. Denoyer A, Denoyer L, Halfon J, Majzoub S, Pisella PJ. Comparative study of aspheric intraocular lenses with negative spherical aberration or no aberration. J Cataract Refract Surg. 2009 Mar;35(3):496-503. doi:10.1016/j.jcrs.2008.11.032. PMID: 19251145.
5. Van den Berg AB, van den Berg RM, Chamon W, Rocha KM. Clinical outcomes and in vivo aberrometry following the implantation of a monofocal IOL with positive asphericity. Clin Ophthalmol. 2025;19:1721-9. doi:10.2147/OPTH.S519332.
6. Stern B, Saad A, Gatinel D. In vitro comparison of an aspherical monofocal lens inducing positive spherical aberrations with a spherical lens. J Refract Surg. 2025 May;41(5):e481-91. doi:10.3928/1081597X-20250403-02. PMID: 40340676.
7. Wilkins MR, Allan BD, Rubin GS, Findl O, Hollick EJ, Bunce C, Xing W; Moorfields IOL Study Group. Randomized trial of multifocal intraocular lenses versus monovision after bilateral cataract surgery. Ophthalmology. 2013 Dec;120(12):2449-55.e1. doi:10.1016/j.ophtha.2013.07.048. PMID: 24070808.