Researchers in ophthalmology have been hot on the trail of presbyopia-correcting intraocular lenses for years, with manufacturers offering myriad multifocal and advanced technology lens options. With several options available, patients aren’t the only ones feeling a little overwhelmed. Surgeons too may find their heads spinning as they browse the choices on today’s market. This sudden surge of new lens options is providing better technology that has fewer optical trade-offs. While there are tradeoffs with any of the lens options, each offers patients visual clarity that would have been unimaginable a generation ago. The ability to provide range of vision while maintaining quality of vision has dramatically improved over the last few years. The key to success with these devices is proper patient selection on the part of the surgical team. When a skilled ophthalmologist is able to pair a patient with the best-suited IOL for their lifestyle, little can stand in the way of patient satisfaction. Thus, part of the surgeon’s job is not only to implant the lens successfully, but to accurately translate the patient’s sometimes imprecise description of their needs into a treatment plan.
This article offers guidance on a number of these new lenses and how to match a patient with the right one to achieve the best possible results.
Toric Lenses for Astigmatism
Toric lenses should be offered to any patient with clinically significant astigmatism since the optics of a monofocal toric lens are equivalent to a monofocal non-toric lens. Our goal should be no more than 0.5 D of residual astigmatism for all patients. For this reason, there is no disadvantage to correcting astigmatism for patients aside from out-of-pocket expenses. Toric lenses are now available in powers as low as 1.25 D at the IOL plane, which corrects 0.9D at the corneal plane, so even lower magnitudes of astigmatism can be corrected with IOLs. The light adjustable lens is approved to be used on patients with 0.75 D of preoperative corneal astigmatism.1 Surgeons can reliably treat lower orders of astigmatism, so the ability to achieve emmetropia and reduce postoperative astigmatism to 0.5 D or less of astigmatism is finally possible. On the high end, toric lenses are available to correct 6.00 D at the IOL plane or 4.11 D at the corneal plane. These extreme powers vary by manufacturer, so when treating very high or very low astigmatism, surgeons may need to plan in advance and order lenses not typically on consignment. Furthermore, there are now toric presbyopia-correcting lenses with improved optics, so we have more options for patients who can afford to correct their vision at the time of cataract surgery.
While some surgeons may still use manual limbal relaxing incisions or femtosecond laser arcuate incisions to treat astigmatism, this has fallen out of favor due to safety, efficacy, predictability, and stability concerns.2-3 Corneal incisions, especially large ones, can result in ocular surface discomfort such as foreign body sensation or even corneal ectasia.2 Furthermore, the effect of these incisions can change over time making long term stability an issue. Given that patients may develop irregular astigmatism, or even worse, occasional full thickness penetration with manual LRIs, the result can be poor visual quality due to high higher order aberrations. A Cochrane review found that toric IOLs probably provide a higher chance of achieving astigmatism within 0.50 D after cataract surgery compared with LRIs.4
For these reasons, correcting astigmatism at the IOL plane is far superior to correcting it at the corneal plane. Now that we have the ability to correct astigmatism as low as 0.50 D in the IOL, corneal or limbal relaxing incisions should be reserved for cases that have very low or very high astigmatism that cannot be corrected with an IOL. For instance, some patients with 0.75 D WTR astigmatism who choose a presbyopia correcting lens could benefit from reduction of their astigmatism to the less-than-or-equal-to 0.50 D range with femto arcuate incisions. Additionally, some patients may have more corneal astigmatism than can be corrected with an IOL, in which case femto arcuates can be combined with toric IOLs. Occasionally, patients may require laser vision correction after toric IOL implantation for very high amounts of astigmatism.
Finally, measuring astigmatism magnitude and axis continues to be one of the most elusive, frustrating hurdles of refractive cataract surgery. Most fastidious refractive cataract surgeons have at least 2 or 3 diagnostic devices to measure astigmatism and obtain 2 or more sets of measurements. Intraoperative aberrometry can be useful as a tie-breaker. It is widely accepted that measuring, or at least accounting for, posterior astigmatism increases refractive accuracy. In fact, several studies have confirmed that posterior corneal astigmatism magnitude and axis orientation cannot be adequately predicted by measuring the anterior corneal curvature alone.5-7 To achieve the best outcome, using modern biometry and the newest generation IOL formulas, such as the Barrett TK toric formula, should increase refractive accuracy.
When discussing different lens options, consider the lens’s performance with respect to range and quality. Of the options available today, the widest range of vision is provided by the trifocal IOL, which provides a full range of vision at distance, intermediate, and near with the defocus curve never dropping below 20/25.8 This is a dramatic change from older generation multifocal lenses, which were essentially bifocal lenses. Historically, surgeons relied on questionnaires, extensive preoperative discussions, and mixing-and-matching to deliver the appropriate range of vision for their patients’ needs. Today, if a patient expresses a desire to be “glasses-free,” the most likely choice to minimize dependence on spectacles is bilateral implantation of trifocal lenses. Of all lenses, this lens is most likely to achieve 20/20 to 20/25 at all ranges.
Of course, patients should still be counseled that they may need readers for fine work or low lighting, but many ultimately do not. The old adage of “under promise, overdeliver” still applies, but patients are more likely to be satisfied with their range of vision with trifocal lenses.9 Every patient should be counseled extensively that they will experience halos at night. Generally, these halos are milder than with older multifocal lenses, and patients are often more willing to allow time for neuroadaptation since their unaided vision is excellent, but there will of course be a small percentage of patients who cannot neuroadapt and may require IOL exchange. It is important to discuss this upfront with patients who are particularly demanding or afraid of committing to this lens choice. Of course, it should be clear to the patient that IOL exchange is a last resort, but it can be helpful for patients to know that there is an option to exchange the IOL if they are in the minority of people who do not adapt. Patient questionnaires can be useful in assessing personalities, but there is really no substitute for talking to your patient and essentially conducting your own evaluation of their personality to understand what they want, what they don’t want, and how likely they are to be satisfied.
Another important point to consider with trifocal lenses is that, due to the diffractive optics, they are particularly sensitive to any residual refractive error or ocular surface disease, so these must be addressed aggressively. Offering an early enhancement to patients with residual refractive error can dramatically improve their opinion of their vision. Furthermore, treating ocular surface disease aggressively with topical steroids, immunomodulators, lubricants, or thermal meibomian gland therapies, or a combination, can improve patients’ quality and stability of vision, increasing satisfaction rates.
Adjustable and Extended Range of Vision Lenses
Prior to 2020, patients who had any ocular pathology — retina, glaucoma, or post-refractive — were often told they were not candidates for advanced technology lenses or, even worse, they received diffractive IOLs with less than ideal outcomes. Fortunately, we now have better options for these patients. The light adjustable lenses on the market have little to no reduction in quality of vision. Of course, light adjustable lenses require a capital investment, but either are excellent options for patients who are not ideal candidates for diffractive lenses. We also have new extended range of vision and monofocal plus lenses that increase range of vision without the compromise in quality of vision of diffractive lenses.