Long-Term Visual Quality after Microincision Cataract Surgery

Purpose Few studies have focused on long-term postoperative visual quality. This study aimed to evaluate the long-term visual quality after microincision cataract surgery (MICS). Methods 96 patients (144 eyes) diagnosed with age-related cataracts were enrolled in this one-year study. The patients underwent MICS and received aspheric monofocal intraocular lens implants. Uncorrected distance visual acuity (UDVA) was evaluated together with best-corrected distance visual acuity (BCDVA), best-corrected near visual acuity (BCNVA), contrast sensitivity, and surgically induced astigmatism (SIA). Results Compared to preoperative measurements, UDVA, BCDVA, and BCNVA were significantly better after surgery (P < 0.001), and they remained stable throughout follow-up. Contrast sensitivity was also significantly better after surgery (P < 0.001). Mean SIA during follow-up was 0.57 ± 0.33 D at 1 week, 0.36 ± 0.25 D at 3 months, and 0.18 ± 0.16 D at 1 year. SIA decreased significantly during the postoperative period (P < 0.001). The 1-year postoperative absolute residual diopter value was 0.32 ± 0.28 D. Conclusion MICS can provide excellent visual quality as soon as on postoperative day 1, which persists during the follow-up period of 1 year. In contrast to previous studies, SIA decreases over time and may not completely stabilize for as long as 1 year postoperatively.


Introduction
Age-related cataract is the leading cause of visual impairment and blindness among elders [1]. Phacoemulsification has now become a mainstream treatment for cataracts [2]. Microincision cataract surgery (MICS), which is performed through an incision of less than 2 mm [3], has been developed as a method of minimizing corneal trauma and providing better postoperative outcomes than standard small incision phacoemulsification [4]. Significant improvements in phacoemulsification techniques and intraocular lens (IOL) technology have turned cataract surgery from an exceptional, sight-saving operation to a routine refractive procedure [5]. Optimally, vision-restoring surgery should increase both visual acuity and quality. Numerous clinical trials indicate that cataract surgery increases visual acuity, but it can also result in surgically induced astigmatism (SIA) [4,6,7], which limits improvements in visual quality. SIA is associated with many factors, including incision size [8], preoperative astigmatism, amount of manipulation during surgery [9], ultrasound technology, and instrumentation [3]. Numerous studies have reported lower SIA after MICS than after regular incision of 2.5-3.0 mm [2,6,[10][11][12]. ese studies suggest that MICS can reduce SIA, accelerate visual rehabilitation, and improve incision integrity. However, most previous studies on SIA involved follow-up of only 1 day to 6 months [2,6,[10][11][12][13].
Few studies, particularly in the long term, have examined how MICS may affect SIA and visual quality like contrast sensitivity. erefore, the aim of this study was to evaluate visual quality in terms of SIA up to 1 year after MICS.

Patients.
is prospective observational clinical study enrolled a total of 96 patients (144 eyes) treated in the study between October 2015 and January 2016. e study protocol followed the guidelines of the Declaration of Helsinki and was approved by the Ethics Committee in our hospital. All patients were informed about the study and provided informed consent before participating.

Inclusion and Exclusion Criteria.
Patients were enrolled consecutively if they were diagnosed with age-related cataracts of grades II-IV according to Emery-Little classification [14] using s slit-lamp microscope (Topcon SL-1E, Tokyo, Japan). Patients were excluded if (a) they had been diagnosed with ocular diseases, such as corneal disorders, glaucoma, active uveitis, and retinal or optical nerve diseases; (b) they had a corneal endothelial cell count of <1500 cells/mm [2]; (c) their axial length exceeded 26.5 mm; or (d) they had a history of ocular surgery or ocular trauma.

Intraoperative Procedures.
All eyes underwent the same MICS procedures using a Stellaris Phaco unit (Bausch & Lomb, USA). After topical anesthesia (Benoxil, 0.4% solution), a corneal incision of 2.0 mm (at around the 10 o'clock position) was made, followed by a second incision at around the 2 o'clock position. Continuous curvilinear capsulorhexis was made with a diameter of approximately 5.0-5.5 mm. After phacoemulsification of the nucleus and irrigation/ aspiration of the remaining cortex, an Akreos MI60 IOL (Bausch & Lomb, USA) was inserted in the capsular bag using an injector system. All surgeries were performed by the same experienced surgeon (W. F.).

Follow-Up.
Postoperative assessments were performed on the day after surgery as well as 1 week, 3 months, and 1 year afterwards. At each follow-up, detailed slit-lamp microscopy and corneal topography were performed, and the following parameters were determined: UDVA, BCDVA, BCNVA, contrast sensitivity, and IOP. SIA was determined using an SIA calculator (http://www.sia-calculator.com). Contrast sensitivity was measured using CSV-1000E (Vector Vision, USA). Anterior segment OCT (AS-OCT) (Carl Zeiss Meditec, Dublin, CA, USA) was performed at 1 week and 3 months postoperatively. Corneal specular microscope was measured preoperatively and at 3 months postoperatively.
2.6. Statistical Analysis. Statistical analysis was performed using SAS 9.2 software. For statistical analysis of visual acuity, logarithms of the minimum angle of resolution (logMAR) were used. Contrast sensitivity values were also log-transformed (Metrovision). Quantitative data were expressed as mean ± SD. Qualitative data were expressed as frequencies and percentiles. Preoperative and postoperative measurements were assessed for significance using the paired-samples t-test and the Wilcoxon signed rank test. Differences across time points were analyzed for significance using analysis of variance (ANOVA) followed by the Dunnet-t-test for differences between groups. Differences associated with P < 0.05 were considered statistically significant.

Visual Acuity and Quality Measurements.
e BCNVA was compared using the Wilcoxon signed rank test and found to be significantly better at every postoperative time point than preoperatively (P < 0.001; Table 1). Figure 3 shows the preoperative and postoperative contrast sensitivity at spatial frequencies of 3, 6, 12, and 18 cycles per degree. For each spatial frequency, contrast sensitivity was significantly higher at every postoperative time point than preoperatively (P < 0.001), and it remained stable for up to 1 year postoperatively. Nevertheless, a decreasing trend was observed at 18 cycles per degree.  Figure 5(a)) and a near normal thickness of cornea at the site of incision (mean 686.83 ± 53.17 μm, P < 0.001) at 3 months ( Figure 5(b)). e mean central corneal thickness was 546.79 ± 40.81 μm at 1 week and 538.61 ± 39.57 μm at 3 months (P � 0.042).

Discussion
is study evaluated visual quality over a period of 1 year after MICS and Akreos MI60 IOL implantation. e data showed significant improvement in UDVA, BCDVA, and BCNVA (Figures 1 and 2 and Table 1). Visual acuity increased significantly within 1 week and remained stable for 1 year postoperatively. A study found that the increase in epithelial thickness and CCT was correlated with CDVA at a near term after cataract surgery [15]. e statistically significant difference of CCT between 1 week and 3 months (P � 0.042) did not seem to affect UDVA and BCDVA at an early time postoperatively. CCT postoperatively was influenced by many factors including phaco time, phaco power, and age [15,16]. Further studies are needed to explore the relationship between CCT and visual acuity. Moreover, the SIA was small (0.36 ± 0.25 D) at 3 months postoperatively. ese results were in line with expected visual outcomes after MICS.
Contrast sensitivity after phacoemulsification has been studied for follow-up periods shorter than one year [6,17,18]. Espíndola et al. [19] reported improved contrast sensitivity after phacoemulsification implantation of an aspherical monofocal IOL with a spherical surface lens, especially at low and intermediate spatial frequencies. Similarly, we found that 2.0 mm microincision phacoemulsification with aspheric monofocal IOL implantation significantly improved contrast sensitivity at low and intermediate spatial frequencies of 3, 6, and 12 cycles per degree between 1 week and 1 year postoperatively. Contrast sensitivity was also significantly increased at 18 cycles per degree, although there was a decreasing trend by 1 year postoperatively ( Figure 3). is may have been caused by posterior capsule opacity, which nevertheless did not cause significant hazy eyesight.
SIA occurs when cataract surgery destroys corneal integrity and is determined by the biomechanical properties of the cornea as well as the incision location, shape, length, type, and suture [20][21][22][23]. Small incisions cause significantly greater SIA than microincisions [10,21]. In our study, mean SIA was 0.18 ± 0.16 D at 1-year follow-up, which is well below the value of 0.5 D, which is considered the upper limit of corneal astigmatism after successful refractive cataract surgery [24]. is may reflect the advantages of MICS and the fact that IOLs in our study were implanted through incisions of only 2.0 mm long.
One of the most interesting findings from our study was the timing of stabilization for SIA. Previous studies of SIA after coaxial MICS was followed up for fewer than 3 months postoperatively [6,25], but SIA is not static: it has been shown to peak soon after surgery and subsequently decrease over time [13]. Indeed, we found that SIA fell significantly between one week and 3 months (Figure 4), corresponding to the significant remission of corneal edema ( Figure 5), and it continued to decrease to as low as 0.18 ± 0.16 D up to 1 year postoperatively.
is is in contrast with studies reporting that SIA remained constant between 1 month [13] and 3 months postoperatively [26]. SIA may decrease as a result of cell migration, restoration of the endothelial barrier, remission of edema that restores corneal curvature [23], and other factors such as changes in corneal biomechanic properties [27,28]. It may take longer for SIA to stabilize than previously reported. Although further study should examine the timing of SIA stabilization, one thing is clear that the SIA from MICS is low enough for refractive cataract surgery and thus makes MICS advantageous to other procedures for patients with premium IOL implantation. e limitation in our study was the lack of anterior segment OCT at 1 year, although the thickness of the cornea at the site of incision almost returned to normal at 3 months.

Conclusion
Our study of MICS suggests that the procedure is safe and effective and can lead to stable outcomes for at least 12 months postoperatively. Improvement in visual acuity and contrast sensitivity occurred soon after surgery and persisted throughout follow-up. On contrary to previous studies, SIA decreased over time and had not stabilized even by 1 year postoperatively.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request. Disclosure e funding organization had no role in the design or conduct of this research.

Conflicts of Interest
e authors have no conflicts of interest in this article.