When implanting and aligning toric IOLs, achieving a precise placement of the lens is critical. Colleagues and I conducted a retrospective study in 2020 in which we looked at sources of error of toric lens power calculations.1 We found that differences in the preoperative keratometry measurements between two devices is a strong predictor of a relatively poor outcome. IOL rotational misalignment and tilt were the second and third most common sources of postimplantation error for toric IOLs.
THE NP-T, NEW PRELOADED TORIC IOL INJECTION SYSTEM
Excellent Intracapsular Stability
To make the implantation of toric IOLs more streamlined and reproducible, NIDEK recently launched the Preloaded Toric IOL Injection System NP-T. For enhanced intracapsular stability, the NP-T IOL features Anchor Wing Loop haptics that provide 154º of contact with the capsular bag. Located 90º apart, the haptics evenly distribute intra- and extra-capsular pressure from capsular contractions to maintain the IOL’s position and prevents rotation (Figure 1).
Figure 1. The Anchor Wing Loop haptics of the NP-T IOL are designed to optimize contact with the capsular bag to enhance stability. Their placement 90º apart allow them to evenly distribute pressure from capsular contractions, further preventing IOL rotation.
The haptics are enhanced with a textured surface that creates friction against the capsular bag for added resistance against IOL rotation. Furthermore, the lens unfolds at an optimized speed, a little slower than nontoric models. In my experience, once the haptics have completely unfolded, it is not easy to rotate the lens in the eye. However, I find the material of the NP-T IOL makes it easy to align the optic and remove viscoelastic from behind it.
IOL Powers
Both the toric and nontoric models of the NP series are available in a wide range of powers to treat more patients (Editor’s note: The availability of models and diopter ranges of the NP-T differs from country to country.). For example, the NP-T IOL comes in myriad cylinder powers, from 0.75 D, which equals approximately 0.52 D on the corneal plane, up to 6.00 D of cylinder diopters, which will correct more than 4.00 D of astigmatism. The lens’ range of spherical powers is similarly broad: essentially 1.00 D up to 30.00 D. All diopter lenses fit through a 2.2- to 2.4-mm incision with the preloaded injection system.
Ease of Use
I find the NP series very easy to use. First, you fill an OVD into the injector’s chamber, and then you depress the plunger that folds and advances the IOL. Dual silicone rings on either side of the plunger create the optimal resistance between the injector and the plunger for smooth, constant pressure during the IOL’s injection.
CLINICAL STUDY
Methods
Colleagues and I conducted a clinical study on the rotational stability of the YST 0.00 lens (the NP-T lens without cylinder power).2 We enrolled 100 eyes of 77 patients who were 18 years or older (median age, 71) who had either a unilateral or bilateral age-related cataract, a potential postoperative BCDVA of 0.2 log MAR (0.63) or better, and a calculated IOL power within the range of an investigational IOL. We evaluated the rotational stability of these IOLs at 1 hour, 1 week, and 6 months postoperatively using retroillumination with a dedicated camera. Using the episcleral vessels in the patients’ eyes as reference points, we were able to determine the rotation of these lenses.
Results
The patients in this study achieved very good visual acuity by 6 months postoperatively: 98% had postoperative BCDVA of 0.63 or better; 95% were within ≥0.8; and 81% were within >1.0. The YST 0.00 lens rotated less than 3º in 74% of eyes, and less than 6º in 98% of eyes. The mean absolute rotation was 2.1º with a very small standard deviation of 1.7º, equally distributed between clockwise or counterclockwise (Figure 2). One comparable study in the literature demonstrated that other IOLs tend to have greater rotation postoperatively; there are only a few lenses that have such a low degree of postoperative rotation.3
Figure 2. By 6 months postoperatively, the YST 0.00 lens showed a mean absolute rotation of 2.1º (SD, 1.7º), in both counterclockwise and clockwise directions. (Reprinted with permission from Ullrich M, et al. Rotational stability and capsular bag performance of a hydrophobic acrylic open-loop single-piece intraocular lens. Eur J Ophthalmol. 2024;34(6):1899-1908).
Using a Purkinje meter to measure decentration and tilt, the YST 0.00 lens demonstrated very low amounts of decentration (Figure 3A), which is better than most other lenses we have tested with this device. Similarly, the lens showed very small degrees of tilt (Figure 3B), which is what we would expect with a good lens and good physiological conditions.
Figure 3A and B. The YST 0.00 lens had minimal decentration of 0.35 mm ± 0.17 mm (A), and a mean pupillary tilt of 4.1º ± 1.9º (B) at 6 months postoperatively. (Reprinted with permission from Ullrich M, et al. Rotational stability and capsular bag performance of a hydrophobic acrylic open-loop single-piece intraocular lens. Eur J Ophthalmol. 2024;34(6):1899-1908).
FOR GREAT TORIC IOL OUTCOMES
The new NIDEK toric IOL provides patients with good postoperative vision and has excellent rotational stability. The new NP series of lenes from NIDEK are stable in the capsular bag, easy to implant via their preloaded injection systems, and carry a wide range of corrective powers for myopia, hyperopia, and astigmatism.
In our clinical study, the lens demonstrated low amounts of rotation, decentration, and tilt at 6 months after surgery. Although some postoperative rotation is a factor with all IOLs, we can minimize this effect by choosing lenses with proven stability. Of course, we must take adequate care with precise measurements, marking, and complete OVD removal from behind the IOL to ensure great outcomes.
1. Hirnschall N, Findl O, Bayer N. Sources of Error in Toric Intraocular Lens Power Calculation. J Refract Surg. 2020;36(10):646-652.
2. Ullrich M, Fisus AD, Palkovits S, et al. Rotational stability and capsular bag performance of a hydrophobic acrylic open-loop single-piece intraocular lens. Eur J Ophthalmol. 2024;34(6):1899-1908.
3. Visser N, Bauer NJC, Nuijts RMMA. Toric intraocular lenses: historical overview, patient selection, IOL calculation, surgical techniques, clinical outcomes, and complications. J Cataract Refract Surg. 2013;39(4):624-37.
