Many surgeons might think that a monofocal IOL is a commodity, but to me, it is not. As technology improves, we become more capable of discerning the differences between them.
The human eye is not a perfect optical system; we see evidence of this when pictures from the IOLMaster 700 show an eye whose optical axis is not aligned with its visual axis, or when the pupil is misaligned with the visual axis or optical axis. Often, the lens inside the eye is decentered from the optical axis, and/or it may be tilted. To date, we don’t have a way of compensating for these misalignments, although there are many studies that show how impactful they can be on image quality.
One study from Rosales et al published in 2010 showed that the average IOL tilt inside the eyes is pretty small—1º to 2.5º—but it is possible for a lens to be tilted up to 5º in healthy eyes.1 Most of the time, the lens is well centered, with less than 0.35 D of decentration. However, a significant number of eyes, perhaps up to 20%, experience more than 0.50 mm of IOL decentration.2
Decentration With Aspheric Optics
Most surgeons have moved on from spherical IOLs to aspheric IOLs, because aspheric optics are supposed to produce better retinal image quality. That’s true, when everything’s perfect; but again, the average eye is not perfect. Decentration quickly degrades image quality for aspheric IOLs. What if we could find a way to work in the middle, where we could maximize the benefits of an aspheric lens when decentration doesn’t matter (like when a pupil is really small), and then try to mitigate the effects of decentration when it does matter (in large pupils). That’s the idea behind the optical profile of the ZEISS CT LUCIA IOLs.
The CT LUCIA 621P IOL
The central optic zone of the CT LUCIA IOL is a hydrophobic acrylic monofocal with variable asphericity. The CT LUCIA 621P has a unique, patented, aspheric ZEISS Optic (ZO) in which the central optical zone has negative spherical aberration to balance positive corneal aberration. Closer to the periphery, the optic transitions gradually from negative asphericity to positive asphericity, which simulates a neutral effect and is less susceptible to decentration. When the pupil is small, the optic of the CT LUCIA 621P performs like a negative aspheric, but as the pupil enlarges, and especially in cases in which it is not centered over the visual axis, it acts more like a neutral aspheric.
In 2022, Borkenstein et al published the results of a study in which they measured the optical performance of 3 IOLs: the Sensar 1-Piece Monofocal (Johnson & Johnson Vision); the Tecnis Monofocal (Johnson & Johnson Vision); and the ZEISS CT LUCIA 621P.3 In MTF measurements, all the lenses performed well when the pupil was small (3 mm) and the IOL was well-centered. When the pupil was small and the IOL was decentered by 1 mm, the performance of all the lenses began to drop, but the CT LUCIA 621P still performed pretty well, especially compared to the negative aspheric IOL. Most impressively, the study showed that when the pupil size was large (4.5 mm), the CT LUCIA 621P demonstrated a high tolerance to decentration and consistent optical performance, having the highest MTF when being decentered while outperforming the spherical IOL when centered (Figure 1). This is how we might expect the lens to perform in the real world—providing optimized visual outcomes for a wide range of cataract patients.
Figure 1. When the pupil was large and the IOL decentered, the CT LUCIA 621P IOL performed the best. (Adapted from Borkenstein AF et al, Ophthalmic Res, 20223).
Figure 2. The CT LUCIA 621P: A high Abbe number equals fewer visual symptoms from chromatic aberration. Left: ZEISS CT LUCIA 621P (V = 51). Right: Bausch + Lomb’s enVista hydrophobic acrylic IOL (V = 40.5).
Clarity of the CT LUCIA IOL
To me, the most impressive thing about this IOL is its clarity. That is what I notice at the slit lamp. An IOL’s clarity really comes down to the purity of its material, refractive index, and in turn, it’s Abbe number (a measure of chromatic aberration). The Abbe number is inversely proportional to the refractive index. Preferably, the refractive index should be higher, because higher refractive indices give us thinner IOLs. But the higher the refractive index, the lower the Abbe number, the more chromatic aberration, and the more scattering of light. If we lower the refractive index just enough, so that it can still get through a 2.0- to 2.4-mm incision, we raise the Abbe number and get less chromatic aberration.
When I look at the CT LUCIA 621P IOLs at the slit lamp, I often can’t see them at all. Other than the light reflex from the cornea and from the anterior hyaloid or the posterior capsule, the front and back surface of this lens is nearly invisible (Figure 2). I implant this lens through a 2.4-mm incision using a wound-assist technique, so I don’t usually put the injector all the way into the anterior chamber. Then I use either a Kuglen Hook or I/A to deposit it in the bag.
Results From the CT LUCIA 611P IDE Registration Trial
I participated in the clinical trial from which the CT LUCIA 611P received FDA approval in the US (and then the 621 was approved via an amendment).4 In the clinical trial, the 611P lens showed a very low rate of PCO: 3% at 1 year and 8.5% at 2 years. Only three patients in the entire study reported mild positive dysphotopsias. It’s an extremely clear lens. It has no glistenings, no haze, and no surface damage noted in a single case across the whole series. Its diopter range is zero to 34.00 D in half-diopter increments.
Summary
The CT LUCIA IOLs are hydrophobic acrylic monofocal lenses with a unique aspheric profile that maximizes visual performance based upon our understanding of real eyes (which all have some level of IOL tilt and decentration). The platform has a high Abbe number and low chromatic aberrations. It’s the most invisible lens that I’ve implanted to date. It’s glistening-free* and has a low rate of PCO and dysphotopsias.
1. Rosales PP, De Castro A, Jiménez-Alfaro I, Marcos S. Intraocular lens alignment from purkinje and Scheimpflug imaging. Clin Exp Optom. 2010;93(6):400-408.
2. Wang X, Dong J, Wang X, Wu Q. IOL tilt and decentration estimation from 3 dimensional reconstruction of OCT image. PLoS One. 2013;8(3):e59109.
3. Borkenstein AF, Borkenstein EM, Luedtke H, Schmid R. Impact of decentration and tilt on spherical, aberration correcting, and specific aspherical intraocular lenses: an optical bench analysis. Ophthalmic Res. 2022;65(4):425-436.
4. Schallhorn SC, Bonilla M, Pantanelli SM. Outcomes of a multicenter U.S. clinical trial of a new monofocal single-piece hydrophobic acrylic IOL. J Cataract Refrac Surg. 2022:1;48(10):1126-1133.
*Clinical Study in US with CT LUCIA 611P of same material did not show any glistenings at 12 months.
