Influence of ocular biometric factors on the defocus curve in an enlarged depth-of-focus intraocular lens

What was known

What this paper adds

Although monocular intraocular lenses (IOLs) have improved the visual quality of patients undergoing cataract surgery, the independence of correction for intermediate and near vision is increasing. In the last decade, several types of multifocal IOLs have been designed to improve spectacle independence after cataract surgery. Unlike the preceding monofocal IOLs, multifocal IOLs provide good visual outcomes at different distances [1]. Moreover, new generation multifocal IOLs have been designed to overcome some disadvantages of previous multifocal IOLs attributable to their inherent optical design, such as the perception of photic phenomena, reduced contrast sensitivity (CS), and decreased visual function in dim light environments [2, 3]. For a successful outcome and meet patients' expectation, it is crucial to consider preoperative factors, including biometric measurements, pupil reactivity or patient’s lifestyle [1].

Tecnis® Symfony® ZXR00 (Abbott Laboratories, Illinois, USA) produces an extended depth of focus in order to improve visual outcomes at intermediate distances. Previous studies have revealed that Tecnis Symfony IOLs exhibit good visual outcomes after surgery [4, 5]. In particular, they provide better objective and subjective quality of vision and CS compared to trifocal lenses and produce less photopic phenomena [5‐7]. Nevertheless, their performance is worse at near vision, and acceptable intermediate vision varies largely among patients. Therefore, the aim of this study was to analyze demographic and preoperative factors related to enlarged postoperative depth-of-focus in patients implanted with Tecnis Symfony ZXR00.

We included 131 eyes from 66 subjects implanted with Tecnis® Symfony® ZXR00 IOL. One eye was excluded because of epiretinal membrane. Demographic and preoperative biometric measurements are represented in Table 1. Briefly, 31 females and 35 males were included aged between 40 and 76 years (mean age, 64.6 ± 6.7 years old). Mean AL was 23.52 ± 0.85 mm, and mean implanted IOL power was 21.48 ± 2.36 D.

In this study, we investigated demographic and preoperative biometric measurements associated with 6-months postoperative range of clear vision of eyes implanted with Tecnis® Symfony® ZXR00 IOL after phacoemulsification. Our results indicate that young age, male sex, and smaller axial length and pupil size were associated with wider range of clear vision at 6-months. These results indicate that even in highly selected patients for IOL implantation (less than 1D corneal astigmatism, low ocular aberrations, no ocular pathology), there are demographic and biometric factors that could predict postoperative range of clear vision.

Tecnis® Symfony® ZXR00 is an EDoF IOL that presents a wide range of sharp vision with minimal associated photic phenomena. The results of this study reveal that postoperative UDVA and CDVA were favorable, achieving proper intermediate VAs and enlarged amplitude of pseudo-accommodation. In addition, subjective optimal correction and postoperative patient satisfaction were high. The studies published over the last two years are in line with the current findings, highlighting good visual outcomes after Tecnis Symfony implantation [8‐12]. However, most authors agree that near vision might be limited in some patients. Even with distance corrected refraction, it has been observed that some patients achieve good visual acuities (≤ 0.1 LogMAR or 0.8 decimal) as near as 20 cm, whereas others only reach a sharp vision until one meter. Some authors have suggested that targeting a mild myopia in non-dominant eye improves postoperative outcomes [10]. The variability in the range of clear vision with multifocal IOL has been attributed to several factors, but the influence on extended focus IOLs has not been extensively explored. In the current study, we found that younger age was associated with wider range of clear vision, which is in line with studies evaluating apparent accommodation in eyes with a monofocal IOLs [13]. Moreover, we also found that male gender was associated with wider range of clear vision in the defocus curve measured at 6 months. However, it should be noted that the youngest patients were all male, and this fact might have confounded the current results. On the other hand, spherical aberration is known to increase the depth of focus, although it deteriorates CS [14]. Furthermore, other preoperative high order aberrations have also been associated with different postoperative vision measurements, mainly in near vision [15]. However, we only found significant associations between preoperative spherical and high order aberrations and postoperative defocus curve with 6-mm pupil size, and not with 4-mm, which is the effective pupil size in mesopic conditions. This could be because patients were highly selected for the present study and pronounced preoperative aberrations were considered an exclusion criterion, narrowing the variability of aberrations for smaller pupil sizes.

Lastly, preoperative photopic pupil size is critical for multifocal IOL implantation [16], being larger pupil sizes correlated with better distance visual acuity and with worse near visual acuity [17, 18]. Still, the relationship with preoperative pupil size and the postoperative range of clear vision has not been explored in EDoF IOLs. According to our results, preoperative pupil size was negatively associated with the range of clear vision, suggesting that patients with larger pupil sizes presented reduced defocus curves. Lastly, ocular biometric measurements change as a function of age and gender [19‐23] and both factors were significantly associated with the outcome of interest. Therefore, all GEE models were adjusted for age and sex. These analyses revealed that axial length was also negatively associated with the range of clear vision. Previous studies have reported that both short axial length and small pupil size predict good near vision after monofocal IOL implantation [23], but their relationship was not explored in EDoF IOLs until now.

This study has several limitations. First, the primary endpoint was the monocular defocus curve measured 6 months after implantation, and no further visual variables were considered, like near and intermediate vision VA or CS or patient satisfaction. However, we believe that the defocus curve is a faithful representation of the dynamic range of clear vision in a single variable. Second, IOL centration was not assessed after IOL implantation, which might have confounded the visual outcomes and the current results. Nevertheless, the EDoF IOLs are more robust against optical quality degradation caused by IOL decentration [24]. Also, the lack of a control group is a major limitation of the current this study, and future works focusing on the performance of EDoF IOLs in comparison with monofocal and multifocal IOLs are needed. Finally, it is important to highlight that we excluded patients with poorer visual performance, like patients with capsular opacification, visual acuity above 0.2 logMAR… so it should be taken into account that our results do not determine the real clinical performance of EDoF lenses. On the other hand, this work has several strengths. The use of GEE overcomes some of the statistical shortcoming of previous studies, in which the intrasubject inter-eye correlation was controlled by including one eye per patients or not controlling at all for this effect. Moreover, as far as we know, this is the first study revealing the association between preoperative demographic and biometric measurements and postoperative range of clear vision after an EDoF IOL implantation and sets the ground for future studies in the field.

In conclusion, the present study demonstrated that age, sex, preoperative pupil size, and preoperative axial length were associated with an enlarged range of clear vision in eyes implanted with Tecnis Symfony ZXR00 IOL. The performance of Tecnis Symfony is expected to be maximized by smaller pupil sizes and axial lengths, and in young patients. Regardless of these variables, Tecnis Symfony provides excellent visual results at distance and at intermediate distances and in different light conditions if patients are carefully selected.