Closing the Distance
How does modest monovision work as a strategy for balancing near and far vision?
When choosing an intraocular lens in patients undergoing cataract surgery, we are often challenged with a patient’s desire to achieve adequate distance vision while maintaining some degree of spectacle independence for near vision. In patients who have expressed the desire for full spectacle independence, multifocal lenses are often considered. However, these options are not without their downsides, as patients may experience a higher rate of night vision disturbances, halos, or glare that reduces their satisfaction with the procedure.
As a result of these ongoing challenges, I began my pursuit of a consistent strategy for modest monovision as early as 2008 to provide a better balance between distance and near vision. I spent many years considering whether it would be feasible to design a custom IOL to specifically enhance this strategy – all of which led me to the concept of positive spherical aberration to extend the depth of focus of a monofocal IOL. Positive, rather than negative, spherical aberration is the key to a modest monofocal approach because it acts in a synergistic fashion with myopia, providing a greater overlap or blending between the distance and near sight on the respective eyes. Positive spherical aberration achieves consistent visual acuity and maintains a smoother transition between distance, intermediate, and near vision.
To make this concept a reality, I partnered with the R&D team at Rayner to research, develop, and bring to market a patented technology: an aspheric IOL with an optimized level of positive spherical aberration designed for use when monovision is sought in cataract surgery.
The enhanced monofocal IOL we developed (RayOne EMV) provides an extended range of vision and is the only available IOL optimized for use with monovision. Results from early testing showed that this new lens can provide on average 2.25 D of extended depth of vision when using a 1 D monovision offset. In addition, the dominant eye is more forgiving of postoperative myopic outcomes compared with extended depth of focus IOLs based on negative asphericity or phase shift technology. As a result of these properties, the patient has clear binocular vision more often than would be possible with a standard monofocal IOL used in the same way, reducing the likelihood of patient complaints related to asthenopia and other effects associated with transitions between near and far vision.
The IOL is designed to optimize for monovision with an expectation of excellent binocular distance vision. In fact, a unique feature of RayOne EMV is a stretched focal point that allows the near eye to contribute to distance vision, even with a -1.0 D offset. From a patient perspective, this allows for more blended vision between the two eyes, which has been reflected in positive patient feedback.
The appearance of the IOL’s optic, even under microscopic conditions, is much like that of other monofocal IOLs, with no zones or rings. The patented feature that sets it apart is enhanced spherical aberration in the center of the lens that gradually reduces at the periphery, allowing for an increased range of functional vision. The diffractive-free design reduces the likelihood of dysphotopsia, which should increase patient satisfaction. Compared with a standard monofocal IOL, RayOne EMV provides better intermediate vision, with 1.25 D of extended range of vision on average.
The level of spectacle independence sits between traditional monofocal IOLs and trifocal IOLs, depending on how the IOL is used. For instance, if this IOL is used with no monovision offset, it offers spectacle independence similar to that provided by available extended depth of focus IOLs. If a surgeon calculates the IOL power with a -1.5 D or more offset in one eye, the ability of the enhanced monofocal to achieve spectacle independence competes with multifocal IOLs that usually have the trade-off of rings or zones. To date, RayOne EMV has not been associated with unwanted effects, such as glare or halos.
When using a monovision approach, ophthalmologists should aim for as close to emmetropia as possible in the distance eye. For the near eye, the target should be determined based on the patient’s previous experience with monovision. Importantly, it is critical to remember that post-operative refraction of up to -0.5 D will still provide very good distance acuity. Though the lens is optimized for monovision, it can also be used with a target of emmetropia in both eyes, providing excellent distance and intermediate vision bilaterally.
The RayOne EMV IOL could be an attractive choice for patients wishing to achieve excellent distance vision while maintaining good intermediate vision and some spectacle independence with near vision. Thanks to the optical design, it is more forgiving in terms of missed target refraction and complements the natural positive spherical aberration of most eyes, which naturally increases the depth of focus. Unlike multifocal IOLs, it is designed to accommodate a wider range of pupil conditions, including variations in decentration and tilt.
That said, I might not consider any aspheric lens in patients with extensive decentration or zonulopathy. I also might exclude its use in patients with pseudoexfoliation syndrome as this could cause late decentration. Likewise, the unique spherical properties of RayOne EMV might further exacerbate pre-existing spherical aberration in patients with previous radial keratotomy.
We are increasingly recognizing the value of better presbyopia correction, as individuals are more likely to engage with screens at near focus in their daily work and leisure time. Instead of focusing on excellent far vision only (at the expense of near vision), I now prefer modest monovision as an appropriate strategy in many of my patients, with a target of about -1.25 D in the more myopic eye. In fact, modest monovision is a popular choice for many surgeons around the world – a third of surgeons on a regular basis according to some estimates. In my practice, I offer it to all patients who achieve 6/9 or better in the first eye, and more than 70 percent select this option rather than targeting emmetropia in both eyes.
Ultimately, I am enthusiastic about modest monovision based on the levels of patient satisfaction I have seen in my own practice. In previous published studies, including my own, the overall satisfaction rate is well over 90 percent because the technique does not compromise the quality of vision. Furthermore, unlike diffractive multifocal and extended depth of focus IOLs, modest monovision is not associated with dysphotopsia, halos, or glare that can further impact patient satisfaction.
In my opinion, this new lens represents a next-generation, premium IOL that offers excellent distance vision while maintaining an extended range of intermediate and near vision and offering significantly more spectacle independence than is seen with standard aspheric monofocal IOLs. This lens offers surgeons a new way to approach modest monovision, and I would encourage you to evaluate the technology in your own practice.
