Focusing on functional vision with monofocal lenses
Quantitative and qualitative improvement in IOL design
Cataract surgery is the most common surgical procedure in the EU, with 4.32 million surgeries performed across the EU member countries in 2021 alone.1 Though the National Institute for Health and Care Excellence guidelines recommend using a reduction in quality of life as the threshold for cataract surgery,2 visual acuity-based quantitative thresholds are still widely used.3 However, visual acuity has not been found to be entirely associated with quality of life after cataract surgery, suggesting that improvement in visual acuity alone is not sufficient for true patient satisfaction.4,5 In recent years, several novel IOLs have been introduced whose innovative designs reflect a trend towards prioritising functional vision. Significant advances in this space are anticipated in the coming years.
Functional vision
As opposed to visual acuity testing, which is done in ideal settings like an ophthalmologist’s practice, functional vision can be defined as the amount of vision required to independently perform activities of daily living.6 Studies have found contrast sensitivity, glare and stereopsis to be better predictors of patient satisfaction after cataract surgery, as these qualitative factors affect one’s visual ability in everyday life, such as with driving at nighttime, seeing through fog or recognising faces.4,7,8
Another aspect of functional vision is visual ability at a range of distances needed to perform activities of daily living. Many tasks are done at intermediate or near distances, especially with use of digital devices.9,10 Intermediate and near vision are also important for leisure and physical activities, which account for most daily activities with increasing age.11
Options for IOL implantation after cataract surgery included monofocal IOLs, which provided clear distance vision but poor intermediate and even worse near vision, or multifocal IOLs, which provided different levels of spectacle independence at the cost of visual quality, and insufficient intermediate vision depending on the power addition.12,13 Hence, both monofocal and multifocal lenses lacked efficacy in terms of functional vision. There was a need for an IOL that provided good intermediate vision and spectacle independence with fewer or no compromises in visual quality; this led to the development of the increased range of focus (IROF) IOLs.
Increased range of focus IOLs
IROF IOLs extend the depth of focus by creating an elongated focal point, providing intermediate vision while preserving distance visual acuity.14 This allows patients to be spectacle independent over a wider range of vision than with monofocal IOLs.15 Since light is focused on a single, albeit elongated, focal point instead of being split and projected simultaneously onto the retina (as in multifocal IOLs), photic phenomena like glares and halos are reduced.15
IROF IOLs achieve extended depth of focus (EDOF) by using different mechanisms of action; e.g. narrowing the aperture (pinhole effect) or by utilising spherical aberrations.14 The IC-8 Apthera (AcuFocus, Inc.) is a small-aperture IOL where an opaque, annular, filtering element of 3.23-mm outer diameter and 1.36-mm inner diameter filters out peripheral, defocused light rays to improve range and quality of vision.14 It has been proven to provide good distance, intermediate, and near vision, with visual quality comparable to a monofocal IOL.16 The Mini WELL IOL (SIFI Medtech) is an aberration-based IOL where the optic is divided into annular zones, with the outermost ring being monofocal, while the middle ring has negative spherical aberration for near vision, and the innermost ring has positive spherical aberration that provides intermediate vision.14 It performs well over all ranges of vision, with excellent intermediate vision and no significant dysphotopsias.17
Other IROF IOLs employ different mechanisms, e.g. diffraction, similar to multifocal IOLs, to reach an EDOF-like effect.14 The most studied example is the TECNIS Symfony IOL (Johnson & Johnson Vision): a bifocal diffractive IOL with low add power for intermediate vision, anterior aspheric surface and posterior achromatic diffractive surface. The echelette design on the posterior surface extends the depth of focus and reduces corneal chromatic aberration (Figure 1).14 While it provides an increased range of focus with high spectacle independence,15 its diffractive design can cause some photic phenomena.18
Non-diffractive IROF IOLs function by modifying the geometry of the IOL optic.14 The lack of diffractive components eliminates photic phenomena, resulting in contrast sensitivity and visual quality similar to that provided by monofocal IOLs while providing more spectacle independence and preserved intermediate vision as compared to monofocal IOLs.19 These are termed enhanced monofocal IOLs.
Enhanced monofocal IOLs
Enhanced monofocal IOLs improve upon the drawbacks of monofocal and multifocal IOLs to provide true functional vision over a wide range of distances. These lenses provide distance and intermediate vision comparable to other IROF IOLs,20 with more correction of functional near vision compared to monofocal IOLs and no compromise in visual quality.19
The first enhanced monofocal IOL was the TECNIS Eyhance IOL (Johnson & Johnson Vision).21 It is characterised by a smooth and continuous increase in IOL power from the periphery to the centre (Figure 2) and a higher-order aspheric design compensating for corneal aberrations, improving intermediate vision while preserving distance vision and achieving quality of vision comparable to monofocal IOLs, as per data from several studies.19,21
The aberration-negative AcrySof IQ Vivity IOL (Alcon) employs a proprietary X-wave wavefront shaping technology (Figure 3) that utilises a plateau on its aspheric anterior surface approximately 1 μm in height along with a small curvature change to stretch the wavefront of oncoming light and create a continuous extended range of focus.14 It has demonstrated good distance and intermediate vision with better spectacle independence than monofocal IOLs while maintaining comparable retinal image quality and high satisfaction rates.22,23 In a recent presentation at the 2023 European Society of Cataract and Refractive Surgeons (ESCRS) Congress, Dr Damien Gatinel noted that diffractive ring-like structures on microscopic examination of the IOL optic in vivo, with patients looking slightly off-centre, correspond with the findings of an optical bench analysis which showed that the central ~1 µm element had a sharp, diffractive edge, resulting in a risk of dysphotopsias with this IOL.24 Further, aberration-negative optics are more sensitive to decentration and tilt, and compromise in visual performance due to IOL decentration has been reported, perhaps due to the small, central optical zone of the lens.25
One of the latest entrants to the group of enhanced monofocal IOLs is the RayOne EMV IOL (Rayner), which has received much attention since its launch in 2020 and a subsequent presentation of data at
the 2023 ESCRS Congress.26 It is the only enhanced monofocal IOL utilising controlled positive spherical aberration in the IOL optic centre to increase the range of clear vision and provide high-quality distance and intermediate vision.27 Its blended edge gradually reduces longitudinal spherical aberration towards the periphery to maintain contrast sensitivity under varying ambient light levels (Figure 4). Early and more recent results
have been promising, demonstrating good distance and intermediate vision with functional useful near vision, no dysphotopsias or decreased contrast, and high patient satisfaction with quality of vision comparable to monofocal IOLs.27-30 The toric version is also available on the same RayOne
IOL platform, which has demonstrated good rotational stability and centration.31–33
The RayOne EMV IOL is the first IOL specifically optimised for mini- or modest-monovision (anisometropia between 0.50 D and 1.50 D).27 It elongates optical performance in the hyperopic direction, imparting some distance vision to the non-dominant eye (typically responsible for near vision in a monovision arrangement), creating a smoother transition between the dominant and non-dominant eye, with the large overlap between both eyes providing a wide range of binocular vision (Figure 5).34
A 1.0-D offset can result in 2.5-D increased depth of field (Figure 5). The IOL directs light rays myopically, providing intermediate vision, as well as hyperopically, giving a wider landing zone to the IOL that makes it forgiving of missed target refraction. Since its launch, RayOne EMV has shown high rates of spectacle independence for distance and intermediate vision, with patients achieving functional near vision and requiring minimal reading addition for reading fine print.27,32 In my own experience, a study of 100 eyes implanted with the RayOne EMV in my practice found postoperative binocular uncorrected visual acuity to be 0.1 logMAR or less for distance in 100% of eyes, 0.4 logMAR or less for intermediate (N8) in 100% of eyes, and 0.4 logMAR or less for near (N8) in 92% of eyes.35
Conclusion
Recent innovations in IOL design now enable surgeons to provide quantitative as well as qualitative visual improvement to patients. In particular, the enhanced monofocal IOLs are a promising group, with priority given to achieving functional vision over a broad range of distances with no loss in the quality of retinal images. With further research and optimisation, these IOLs can become the preferred choice for both surgeons and patients in the coming years.
References
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Sanjay Mantry, MD, FRCS, FRCOphth | e: sanjay@visionscotland.com
Mantry is a consultant ophthalmologist with interest in cornea, cataract and refractive surgery. He is the founder and managing director at Vision Scotland.
Financial disclosure: Mr Mantry is a consultant of Rayner.
Miss Catriona Kennedy, MCOptom
Kennedy is a refractive and independent prescribing optometrist who has worked for Vision Scotland since 2019. She provides pre-surgery assessments and post-operative care.
