The tolerance of refractive errors of extended depth of focus intraocular lens in patients with previous corneal refractive surgery

To evaluate the tolerance for refractive errors and visual outcomes of extended depth of focus intraocular lens (EDOF IOLs) in patients with previous corneal refractive surgery for myopia. Patients from Aier Eye Hospital of Wuhan University with previous myopia excimer laser correction underwent cataract surgery and implantation of an EDOF IOL. The follow-up period was three months. The uncorrected distance, intermediate, and near visual acuities (UDVA, UIVA, UNVA), corrected distance visual acuity (CDVA), spherical equivalent (SE), defocus curve, optical quality, including modulation transfer functions (MTF) and Strehl ratio (SR), National Eye Institute Visual Functioning Questionnaire-14 for Chinese people (VF-14-CN), spectacle independence, and dysphotopsia were assessed. At the final visit, UDVA, CDVA, UIVA, and UNVA (LogMAR) were 0.06 ± 0.09, 0.01 ± 0.06, 0.11 ± 0.08, 0.20 ± 0.10, respectively. The mean spherical equivalent (SE) was − 0.57 ± 0.58D, sphere and cylinder were − 0.24 ± 0.60D, − 0.70 ± 0.58D respectively. No statistical difference in UDVA between eyes with SE in ± 0.50 D and in ± 1.0 D (p > 0.05). Corneal astigmatism > 1.00D has no significant effect on postoperative visual acuity (p > 0.05). The defocus curve showed that visual acuity could reach 0.2 in the refractive range of + 0.50D ~ − 1.50D. SR and MTF values were all higher than before the surgery. In bilateral implantation patients, the VF-14-CN questionnaire score and visual quality were quite excellent. The EDOF IOL have a certain tolerance for refractive errors and corneal astigmatism, and it’s recommended for patients with prior myopia excimer laser surgery to achieve satisfactory visual performance.


Introduction
Since the excimer laser was first used in corneal refractive surgery, millions of patients with refractive errors have been treated. With aging, many of these patients develop cataracts and presbyopia [1]. Compared with other patients with age-related cataracts, patients with a history of corneal refractive surgery tend to have a stronger desire for independence from spectacles and higher expectations regarding postoperative outcomes [2]. Therefore, functional intraocular lenses (IOLs) that can correct presbyopia may be the appropriate choice for these individuals, including multifocal, extended depth of focus (EDOF) IOLs, and adjustable IOLs [3]. However, accurate IOL power calculation is difficult for patients with prior myopic refractive surgery due to errors in preoperative corneal curvature measurement and postoperative effective lens position estimation [4,5]. Moreover, it is not uncommon to encounter postoperative refractive error in these individuals. Previous studies have shown that EDOF IOLs have a higher tolerance for refractive errors in comparison to other multifocal or monofocal IOLs because of their unique design. Carones et al. found that EDOF IOLs retained good visual acuity even with an induced astigmatism of − 1.50D [6][7][8]. However, no studies have evaluated the tolerance of EDOF IOLs in patients with previous myopic corneal refractive surgery. This study aims to address this question.

Patients
The retrospective study enrolled patients who underwent cataract surgery and implantation of an EDOF IOL (Tecnis Symfony, Johnson & Johnson Vision Care, Inc.). All patients had previous myopia excimer laser-assisted in situ keratomileusis (LASIK) correction. The study was approved by the Institutional Review Board of Aier Eye Hospital of Wuhan University (2021IRBKY1011). All tenets of the Declaration of Helsinki were followed.
The inclusion criteria [9] included patients with a significant bilateral cataract, previous myopic LASIK, seeking spectacle independence, corneal higher-order aberrations (HOAs) up to 0.50 μm, regular corneal astigmatism ≤ 1.50D, and kappa and alpha angles both < 0.50 mm, without any contraindications of surgical therapy in the preoperative examination or posterior capsular rupture or zonular dialysis during the cataract surgery. Exclusion criteria included previous ocular surgery other than LASIK, active ocular and/ or systemic disease, glaucoma, uveitis, diabetes with retinal damage, and any retinal or macular disease.

Examinations
All enrolled patients underwent routine eye examinations prior to surgery to rule out ocular surface diseases such as dry eye, which included following ophthalmologic preoperative examinations: noncontact specular microscopy, intraocular pressure, uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction. The axial length (AL), keratometry (K) and anterior chamber depth (ACD) were measured using an optical biometry (IOL-master 700, Carl Zeiss Meditec). Corneal tomography (Pentacam HR, Oculus Optikgerate GmbH) was performed to confirm the regularity of the previous ablation and astigmatism through corneal HOA in 4 mm zone. A ray tracing aberrometry (iTrace, Tracey Technologies) was used to measure modulation transfer functions (MTF), and the Strehl's ratio (SR). The OPD ScanIII (Topcon, Japan) was used to measure pupil diameter (PD) and corneal higher-order aberrations (HOAs) in 4 mm PD.
At the three-month postoperative visit, the following parameters were measured: UDVA and CDVA, uncorrected near visual acuity (UNVA) at 40 cm, and uncorrected intermediate visual acuity (UIVA) at 80 cm using the Early Treatment Diabetic Retinopathy Study charts (ETDRs, Wehen Vision Technology Co., Ltd.) designed for these distances, subjective manifest refraction (spherical equivalent, SE), and the defocus curve with distance-uncorrected vision (logMAR acuity) from + 1.00D to − 4.00D in steps of 0.50D. At a pupil diameter of 3 mm, the MTF and SR were measured by iTrace after removing the effects of low-order aberrations. Then, we used questionnaires to assess the quality of life of patients, including the Chinese Visual Function index 14 (VF-14-CN) questionnaire and another short questionnaire about negative visual symptoms, such as halo, glare, and starburst, as well as spectacle independence rate and satisfaction. VF-14-CN is based on 14 uncorrected vision-dependent daily activities, with each item scored on its degree of difficulty as follows: no difficulty (4 score), a little difficulty (3 score), moderate difficulty (2 score), quite difficult (1 score), or impossible to perform the task (0 score). The resulting VF-14-CN score ranged from 0 (worst functional impairment) to 64 (no disability).

Surgical technique
All surgeries were performed by the same experienced surgeon (Y.W.), who used 0.5% compound tropicamide eye drops to dilate the pupils and obucaine eye drops to maintain topical anesthesia before surgery. Capsulotomies (diameters were all set at 5.5 mm) and lens fragmentation were performed using a LenSx femtosecond laser (Alcon Laboratories, Inc., Fort Worth, Texas, USA). Then, standard phacoemulsification cataract surgery was performed. The EDOF IOL (Tecnis Symfony) was implanted in the capsular bag. The residual viscoelastics were removed, and the position of the lens was adjusted. All incisions were hydrated, and the patients' conjunctival sac was treated with dexamethasone tobramycin ophthalmic ointment.

Lens power calculation
A multi-formula average method was utilized for lens power calculation, including three formulas using no previous data from the Hagis-L [10], Barrett True K no-history [11], Shammas no-history [12]. The target refraction was set to postoperative emmetropia. Then, the average of the results calculated by these formulas was used as the implanted IOL power.

Statistical analysis
Statistical analysis was performed using SPSS software for Windows (version 23.0, International Business Machines Corp.). Each index was described as the mean ± standard deviation (SD). Kruskal-Wallis H test was used for 3 groups' data analysis and Mann-Whitney U test was used for 2 groups. Wilcoxon matched-pairs signed rank test was used for comparison of preoperative and postoperative data. Differences were considered statistically significant when the P-value was less than 0.05. All figures were drawn using GraphPad software (version 8.0.2, USA).

Demographics of the patients
A total of 66 eyes of 41 patients were enrolled in this study, including 15 males and 26 females. Table 1 summarizes the demographic characteristics. The mean age of these patients was 49.47 ± 5.68 (range, 37-62 years). A total of 16 (39%) and 25 patients (61%) underwent unilateral and bilateral implantation respectively. The mean axial length was 28.10 ± 1.86 mm (range, 24.56-34.30 mm), and the mean keratometry was 38.27 ± 2.17D (range, 32.7-42.76D). The preoperative mean UDVA of the patients was 0.94 ± 0.36. The preoperative mean CDVA was 0.35 ± 0.17. As shown in Table 1, the mean power of the implanted ZXR00 IOL was 17.98 ± 3.08D (range, 10.5-24D). All patients had no significant dry eye or ocular surface disease, and ocular medications were discontinued in 3 months post-surgery.

Visual and refractive outcomes
The mean UDVA of patients three months after surgery was 0.06 ± 0.09, of which 85% ≤ 0.1. The mean postoperative CDVA was 0.01 ± 0.06, UIVA was 0.11 ± 0.08, and UNVA was 0.20 ± 0.10. The mean postoperative SE = − 0.57 ± 0.58D. 48% (32 eyes) within ± 0.50D, 71% (47 eyes) within ± 1.00 D, and all eyes within ± 1.50D. The mean sphere and cylinder were − 0.24 ± 0.60D, − 0.70 ± 0.58D respectively. An analysis of the visual acuity of the eyes with different SE is shown in Table 2. There was no statistical difference in UDVA between eyes with SE in ± 0.50 D compared to SE in ± 1.0 D. But the eyes with SE in ± 0.50D and SE in ± 1.5D have significantly different UDVA. However, no statistical difference was seen between eyes with different SE for UIVA and UNVA. There are 13 eyes with corneal astigmatism > 1.00D. A comparison of visual acuity and optometry in eyes with different corneal astigmatism is shown in Table 3. Corneal astigmatism > 1.00D has no significant effect on postoperative visual acuity.

Defocus curve
The defocus curve under best corrected visual acuity shows a peak between + 0.50D and − 1.50D and a slow downward trend in the refractive range of − 2.00D to − 4.00D. Visual acuity deteriorates as negative spherical defocus level increases. In  the + 0.50D ~ − 1. 50D refractive range, visual acuity is stable and could reach more than 0.2 LogMAR (Fig. 1).

Postoperative MTF and SR
Comparison of the preoperative and postoperative MTF of patients with a pupil diameter of 3 mm after removing the influence of low-order aberrations showed that the postoperative MTF values at the six spatial frequencies of 5, 10, 15, 20, 25, and 30 c/d were all higher than those before the operation. The differences were statistically significant (P < 0.001). Further, postoperative SR was higher than preoperative SR, and the difference was also statistically significant (P < 0.001) (   Only 2 patients thought it affected their visual acuity. See Fig. 2 and Fig. 3 for more details.

Discussion
For ophthalmologists, there are two major challenges in cataract surgery for patients with previous corneal refractive surgery: IOL power calculation and IOL selection [13]. This study explored the tolerance of refractive errors and early clinical outcomes of EDOF IOL implantation in cataract patients with previous myopia excimer laser correction in order to provide a reference for the clinical application of IOLs. The Tecnis Symfony IOL is a single-piece, hydrophobic acrylic, foldable lens with a biconvex, wavefrontdesigned anterior aspheric surface and posterior achromatic diffractive surface with an echelette design (intended to extend the range of vision by correcting chromatic aberrations) [3,14]. Currently, there are few reports on the implantation of EDOF IOLs in cataract patients with previous corneal refractive surgery.
At three months postoperatively, most patients achieve satisfactory UDVA, but it is inevitable that there will be a certain degree of refractive error, which will not significantly affect the patient's UDVA. After correcting the refractive error, only one extra line can be seen on the eyesight chart, or the same as with the UDVA. Mild postoperative refractive error (SE within ± 1.50D) and corneal astigmatism in 1.50D have no significant effect on postoperative visual acuity. Compared with cataract patients without a history of corneal refractive surgery, those with previous corneal refractive surgery have larger refractive errors after cataract surgery [15,16]. The reason for this may be the extended range vision design of this IOL. Some reports [6][7][8] also indicated that the Tecnis Symfony IOL has refractive error tolerance. Compared with the monofocal IOLs on the same platform, the impact of residual refractive error of Tecnis Symfony IOL implantation is limited in postoperative UDVA. Based on this result, this IOL is suitable for patients with previous corneal refractive surgery, as achieving satisfactory results in eyes with a history of corneal refractive surgery is complicated In the study, the postoperative UDVA of patients was better than UIVA and UNVA, which is consistent with some studies on the Tecnis Symfony IOL [17][18][19]. The Tecnis Symfony IOL has a near additional power of + 1.75D. Theoretically, the focal length of the intraocular lens is 57 cm away from the front of the eye, so the patient's visual acuity is lower at 40 cm in front of the eye. This result suggests that patients may need to wear reading glasses when viewing at close distances after surgery, which may affect some jobs that require better near vision. However, according to the follow-up survey results, in most cases this does not affect the patients' life, and they can achieve spectacle independence. In addition, according to some reports [15,20,21], compared with monofocal IOLs, the visual range is wider, but compared with multifocal IOLs, the visual acuity at near and intermediate distances is insufficient. As the defocus curve shows, full vision can be achieved to a certain extent after IOL implantation, meeting the lens removal needs of cataract patients.
The postoperative MTF values of the patients in the five spatial frequencies were all higher than those before the operation, and the SR was also higher than before the operation. MTF and SR are comprehensive evaluation indexes of visual image quality [22]. Studies have shown that IOLs can enable patients to achieve better visual contrast sensitivity [17,23,24]. However, the study did not include a control group. Although the achromatic design of this IOL can increase contrast sensitivity, the improvement in the patient's visual quality is also related to cataract removal.
All patients with bilateral implantation had higher VF-14-CN scores after surgery. In the postoperative follow-up survey, some patients reported that they had difficulties seeing small print and doing fine work, but on the whole, they had a good quality of life after surgery. Most patients no longer need to wear glasses at different working distances. However, some people occasionally experience a mild glare and halo, which usually appear at night and do not affect the quality of life and vision. It has been reported [23,25,26] that patients with Symfony IOL implantation have a high rate of spectacle independence, and these patients are more satisfied with the operation. Therefore, Symfony IOLs can be considered for cataract patients with previous corneal refractive surgery.
A limitation of this study is that the sample size was too small. In the future, it is necessary to further evaluate the clinical effect of Symfony IOL implantation in cataract patients after corneal refractive surgery with a large sample size, increase the number of indicators, and extend the follow-up time.

Conclusion
In summary, our preliminary findings show that the EDOF IOL has a certain tolerance for refractive errors and corneal astigmatism, and it might provide patients who have undergone LASIK surgery with improved visual outcomes and a higher quality of life.

What Was Learned
1. The EDOF IOLs can provided excellent visual outcomes and high patient satisfaction and have certain tolerance to residual postoperative refractive errors in patients without previous refractive laser surgery. 2. The accurate calculation of intraocular lens power after refractive laser surgery is difficult.

What this Paper Adds
1. The EDOF IOLs have a certain tolerance for refractive errors and corneal astigmatism in patients with previous refractive laser surgery. 2. The EDOF IOLs can provide better visual outcomes and higher quality of life for patients who have undergone refractive laser surgery.

Data availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare no competing interests.
Ethical approval The study was approved by the Institutional Review Board of Aier Eye Hospital of Wuhan University (ID:2021IRBKY1011). All enrolled patients were treated inaccordance with the tenets of the Declaration of Helsinki. Due to the retrospective nature of the study,the need for informed consent was waived by the Institutional Review Board of Aier Eye Hospital ofWuhan University.
Consent for publication Not applicable.