Understanding & Managing Astigmatism Series: Toric Multifocal Optimization

When determining the best contact lens for your presbyopic astigmats, it’s first important to clearly understand ocular optics and how these can change over time. As mentioned previously, typically between the ages of 40 and 50, both the magnitude and type of astigmatic error that patients are likely to experience shift—resulting in both increases in the prevalence of greater astigmatic error and against-the-rule astigmatism.

Alongside this, as Dr. Moody explains, sharing data that he and his team published in 2015, the pupil also changes.1 “We conducted the largest ever pupil study that’s ever been done—evaluating over 500 pupils,” he says. “The first thing we found was a direct relationship between a patient’s refractive error and their pupil size; the second was that as patients age, their pupils become smaller and less responsive.”

Combined, these two findings explain why we can see substantial differences in retinal area and illumination. “If I compared a hyperopic older pupil to a myopic younger pupil, there’s going to be a 28% difference in the retinal area. We need to be considerate of the specifics of a patient’s pupil when thinking about the optical impact of the lenses we prescribe.”

Going by the numbers, it’s likely that you have existing soft single vision toric lens wearers who are approaching or moving through presbyopia and are looking for a contact lens that corrects both astigmatism and presbyopia—what options are available to them? “Historically, we made a lot of compromises in these patients,” recalls Dr. Rueff. “There’s the option of a patient using reading glasses as an on-again-off-again solution, but this is becoming much less acceptable for many of my active presbyopic patients.”

When it comes to contact lens options, monovision lenses, in which one eye is corrected for distance and the other for near, have historically been the go-to choice. “Although I do have a lot of patients who are doing well in monovision, it’s important to remember that monovision only exists because we historically had to compromise when it came to parameters,” she says. “As a solution, it permits clear vision at two distinct distances, but everything in between is blurry, and it also eliminates depth perception. It may historically have been our choice, but there are new toric multifocal options coming to market that we can move some of these patients to, to prevent them from dropping out of contact lens wear altogether.”

But even before the emergence of these new toric options, you might have tried and had success with multifocal spherical lenses. Compared to a single vision lens, which focuses light onto a singular distance point—resulting in blurred vision when astigmatism inevitably shifts a patient’s retinal plane in front or behind this focal point—an extended depth of focus (EDOF) multifocal lens creates a ‘box of vision clarity’ in which, regardless of where the retina focuses, the quality of the visual image remains the same.2

It's important to note that not all EDOF lenses work in the same way. “Although an EDOF optic could be argued to be anything that takes the focal point and extends it, the original idea was that such a lens would make the transition from distance to intermediate to near vision as smooth as possible,” Dr. Moody explains. “This requires a continuous aspheric design—something that only Johnson & Johnson Vision and Alcon currently employ, with only the former also creating multiple power profiles. All other EDOF lenses use a ring design, which is sometimes aspherized, meaning that although the depth of field is being extended, it’s in a staggered way.”

The new ACUVE OASYS MAX multifocal brings the EDOF optics in a toric lens package. “This new lens has a single cylinder power—1.0 D—but because of its multifocal optics, it’s able to correct a range of cylinder powers beyond just our 1.0 D astigmatic patients.” As Dr. Moody explains, this lens should be your first port of call for your patients with 0.75 D of astigmatic error. “To date, we've typically fitted these patients with spherical multifocals, and, generally, they do pretty well. But, if we compare their final residual correction to a patient corrected with a multifocal toric lens, patients will have 0.5 D less uncorrected astigmatism when fitted with a toric multifocal—which is a huge difference.” So, when should you move a patient from a spherical multifocal to its toric counterpart? “My general rule is, if you’re dealing with the non-dominant eye and the patient has 0.75 D of against-the-rule astigmatism, I’d probably leave them in the spherical lens, but if it's with-the-rule in the dominant eye, fit them with the soft toric multifocal.”

There’s also the developing area of miotics. “From an optics standpoint, they make sense,” says Dr. Moody. “If we restrict the pupil to a little less than two millimeters, according to the Riley Constant, we should expect patients to have EDOF in their near vision. I’ve read the emerging data, and it’s exciting—people in their 50s and 60s are able to read the newspaper. But there is a cost: some dimming of the vision. These new alternatives are exciting, but we must consider both the pros and cons.”

Getting your calculations correct and selecting the right pair of multifocals is crucial. “Keep in mind that even 0.25 D here or there can either make or break the fit—you want to pull the right lenses straight out of the gate,” explains Dr. Rueff. This is why she and Dr. Moody both recommend eyecare practitioners use the new ACUVE Vision fitting calculator to ensure that you fit your patients with the right lenses from the get-go. “The fitting guide allows you to input a patient’s parameters and then calculates exactly what lens to pull based off of factors such as age, dominant eye, and vertex prescription—and will vertex correct both sphere and cylinder. I’m sure you’ll see, if you challenge yourself to quickly do these calculations in your head before using the calculator, just how often you’re off in your calculations—which you really don’t want.”

But ultimately, providing your patients with the right pair of contact lenses isn’t just about the numbers, but taking a personalized corrective path. “As the optometrist, you know the patient inside out, so don't be afraid to customize your approach,” advises Dr. Moody—something Dr. Rueff agrees with. “It's definitely more of an art than a science,” she says. “We can also be hesitant to offer multiple solutions because we fear patients won’t be receptive. However, almost every time they’ll actually feel seen and that you've been thoughtful about their individual needs; it can be how you get a patient for life.”