Mastering the balancing act with presbyopia-correcting IOLs
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With cataract surgery, our primary goal is simple: to improve visual quality by eliminating the symptoms of poor contrast, blurred vision and glare from the cataract.
With a monofocal lens, we can also correct preexisting refractive errors, frequently improving patients’ uncorrected distance visual acuity. There are no optical compromises — until the patient wants to see at near.
Source: Daniel H. Chang, MD
Challenges of providing a range of vision
With the growing importance of intermediate and near visual tasks in our modern world, presbyopia-correcting or visual range IOLs can provide the ability to see distance, intermediate and near without glasses. With this extended depth of field or visual range comes potential compromises in visual quality and visual symptoms (Figure 1). Visual quality problems include low contrast, blur and shadows, primarily in photopic conditions. Visual symptoms, specifically low-light dysphotopsias, include glare/flare, halos and starbursts around a point source of light, primarily in mesopic and scotopic conditions (Figure 2). While visual quality and visual symptoms are two sides of the same coin, it is helpful to consider them separately. The second part of this series will cover specific dysphotopsias and how to counsel patients about them in more detail. For now, suffice it to say that visual symptoms are directly related to visual range: the greater the range, the greater the symptoms.
With the primary goal of improving visual quality, we must understand the impact that visual range IOLs have on visual quality. Specifically, how sharply does the lens focus an image? How much contrast is lost? Does a given optotype have a shadow around it? While we typically measure visual quality in photopic, high-contrast conditions — reading a brightly lit black-and-white eye chart in an exam lane — visual quality also comprises patients’ ability to see in more challenging low-light and low-contrast conditions.
Visual quality in the real world
Typically, the greater the visual range an IOL provides, the greater the potential reduction in visual quality. When used to increase visual range, both refractive and diffractive optics can erode contrast, but they are far from the only factors that degrade visual quality. The real and frequently unrecognized enemy of visual quality is optical aberrations, which are influenced not just by refractive/diffractive optical designs but importantly by the IOL material properties themselves. A monofocal IOL with poor spherical aberration and chromatic aberration can provide worse visual quality than some visual range IOLs. Therefore, instead of focusing merely on purported mechanisms of action (refractive vs. diffractive), attention should be focused on aberrations and image quality.
In addition to intrinsic IOL properties, a poorly positioned IOL can degrade visual quality as well. Tilt, decentration and toric misalignment can result in residual postoperative astigmatism and higher-order aberrations. Other circumstances, such as ocular surface problems and other ocular pathologies, can erode visual quality further.
In low-light conditions such as driving at night, poor visual quality is also a problem. While dysphotopsias are typically discussed, low-contrast visual acuity with glare is arguably more relevant. Glare, halos and starbursts can be bothersome, but the ability to see the road, cars and pedestrians beyond the photic phenomena is likely more important to driving safety and comfort. With poor contrast, even in the absence of dysphotopsias, a patient would still not be able to read road signs or to see a person crossing the street. Further, mild halos or starbursts can be tolerable if the patient has good low-light contrast and is able to see the sign or the pedestrian clearly through the dysphotopsias.
Improving visual quality and dysphotopsias
Because tradeoffs in visual quality and visual symptoms are inevitable with visual range IOLs, it is helpful to compensate for these compromises with enabling technologies. This is the approach taken by the latest iteration of Tecnis IOLs (Johnson & Johnson Vision) with InteliLight. Built on a platform with a low-chromatic aberration material, compensation for corneal spherical aberration and active correction of corneal chromatic aberration, the Tecnis Odyssey and Tecnis Symfony OptiBlue IOLs have a violet light-filtering chromophore and are manufactured with a high-resolution lathing process that optimizes the echelette configuration and minimizes residual lathe marks on the optical surface to reduce light scatter and improve contrast under challenging light conditions.
The violet light filter and high-resolution lathing reduce retinal veiling luminance (glare) by up to 17% and provide up to a 13% enhancement in contrast vision under challenging light conditions. A fresh look at data from a prior study of a violet light-filtering monofocal lens shows that patients with a violet light-filtering lens had less visual difficulty while driving, both during the day and at night, compared with those with a colorless IOL (Figure 3).
In a retrospective study conducted in my practice, the violet light filtering and high-resolution lathing of the Tecnis Symfony OptiBlue IOL resulted in up to 45% reduction in dysphotopsia complaints and up to 72% reduction in counseling needed related to dysphotopsias compared with the legacy Tecnis Symfony IOL.
I also participated in an ambispective multicenter clinical study with the new Tecnis Odyssey full vision range IOL with a digitally optimized freeform diffractive profile. We found 94% satisfaction with overall vision and 96% satisfaction with reading a smartphone or tablet without glasses. In a separate multicenter retrospective study, 93% reported no or mild glare, halos or starbursts at 1 month postop.
Fully correcting astigmatism, perfecting one’s approach to toric power calculations, identifying and marking the axis, and using IOLs with excellent rotational stability can also help to ensure that astigmatic error is not the cause of poor visual quality.
While it is not possible to have presbyopia correction without compromises, the latest advances suggest that it is possible to provide full visual range while maintaining high visual quality and minimizing visual symptoms. That sounds like the right balance to me.
- References:
- Chang DH, et al. Clin Ophthalmol. 2022;doi:10.2147/OPTH.S389304.
- Chang DH, et al. Ophthalmol Ther. 2023;doi:10.1007/s40123-023-00709-w.
- Chang DH, et al. The effect of violet light filtration and manufacturing improvements on the clinical performance of an extended depth of focus IOL. Presented at: American Society of Cataract and Refractive Surgery meeting; April 22-26, 2022; Washington.
- Van der Mooren M, et al. Clin Ophthalmol. 2023;doi:10.2147/OPTH.S396823.
- For more information:
- Daniel H. Chang, MD, of Empire Eye and Laser Center in Bakersfield, California, can be reached at dchang@empireeyeandlaser.com.
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