Longer axial length is associated with better prediction for refractive error after sutureless flanged intrascleral fixation of intraocular lens

Abstract

Objective

To investigate refractive outcomes and associated factors after sutureless flanged intrascleral fixation of intraocular lens (SFIF-IOL).

Methods

We retrospectively reviewed the medical records of consecutive patients who underwent SFIF-IOL at a single centre. The prediction error (PE; difference between the achieved and target refractive error) and absolute PE (APE) were analysed. Risk factors associated with refractive surprise, defined as APE > +0.5 D, were investigated using multivariable logistic regression analysis.

Results

Ninety-one eyes were included. At the final follow-up, the mean PE and APE were +0.07 ± 0.88 and +0.68 ± 0.56 D, respectively. Refractive surprise was observed in 44 eyes (54.3%) and was associated with a shorter axial length (AL) [odds ratio, 0.825; 95% confidence interval, 0.688–0.991; P = 0.039]. APE showed a significant correlation with AL at the final visit (⍴ = −0.269, P = 0.010), and eyes with AL ≥ 26 mm had significantly lower APE than did those with AL of 24–26 mm (P = 0.021) and AL < 24 mm (P = 0.0059).

Conclusions

The refractive outcome after SFIF-IOL using manufacturer’s A constant was favourable on average. Eyes with a longer AL were more likely to show a smaller deviation from the target refraction.

Introduction

Scleral fixation of an intraocular lens (IOL) has been widely performed for eyes with limited support from lens capsules or zonules of the ciliary body [1–4]. For decades, sutured scleral fixation has been the most popular surgical technique. However, several suture-related postoperative complications have been reported. Breakage of the fixation suture leads to IOL dislocation [5]. When the remaining sutures are exposed, they may become a possible source of infectious endophthalmitis [6].

Recently, a new technique involving sutureless flanged intrascleral fixation of IOL (SFIF-IOL) has been proposed [5]. Without the use of fixation sutures or fibrin glue, the flanged haptics remain in a stable position; moreover, the possibility of infection is reduced. The procedures are simple, thus requiring a significantly shorter surgery time than that required for sutured scleral fixation [7]. Moreover, it results in less postoperative astigmatism, which suggests less frequent IOL tilt [8].

The primary purpose of IOL insertion is to achieve the target refractive error. However, the refractive outcome after scleral fixation of IOL is reportedly worse than that after in-the-bag IOL insertion [9]. Till date, refractive outcomes after SFIF-IOL have been inconsistent. While some studies reported myopic refractive error shifts [6, 10], others showed mean prediction errors (PEs) that indicated emmetropia or hyperopia [9, 11]. However, only few studies have analysed the influence of clinical and ocular factors on prediction of the refractive outcome after SFIF-IOL. Accordingly, the aim of the present study was to investigate the refractive outcome after SFIF-IOL and determine the risk factors for greater deviation from the target refraction.

Methods

In this retrospective study, we reviewed the medical records of consecutive patients who underwent SFIF-IOL at Seoul National University Hospital, Seoul, Republic of Korea from January 1, 2018 to June 30, 2022. All procedures were conducted according to the tenets of the Declaration of Helsinki, and the study design was approved by the Institutional Review Board of the Seoul National University Hospital (IRB 2301-002-1390), which waived the need for written informed consent because of the retrospective design of the study and the use of deidentified patient information.

The exclusion criteria were as follows: (1) concomitant glaucoma surgery, retinal surgery, corneal surgery, or other intraocular surgeries that can affect the refractive outcome, (2) severe postoperative complications requiring additional vitrectomy, (3) unmeasurable axial length (AL), and (4) lack of postoperative refraction data examined at ≥4 weeks after SFIF-IOL.

All patients underwent a comprehensive ophthalmologic examination before SFIF-IOL; the examination included best-corrected visual acuity (BCVA) assessment, manifest refraction, slit-lamp biomicroscopy, dilated funduscopic examination, keratometry (RKT-7700; Nidek, Hiroshi, Japan), and AL measurement (IOLMaster 700;Carl Zeiss Meditec, Dublin, CA, USA). Preoperative IOL power calculations were performed using the Sanders–Retzlaff–Kraff theoretical (SRK-T) formula, which has been formulated for IOL placement within the capsular bag. The target refractive error calculated by SRK-T formula was based on the manufacturer’s recommended A constant, which was 118.7. There was no adjustment or modification of A-constant. All patients were routinely examined at 1 day, 1 week, and 4 weeks after SFIF-IOL, and a further follow-up schedule was determined at the discretion of the treating physician.

Surgical technique

Surgical indications in the present study included various conditions regarding lens status; phakic, aphakic, subluxated, or dislocated crystalline lens; subluxated or dislocated IOL; and IOL opacity. All patients underwent standard 25-gauge three-port vitrectomy, and the procedures were modified according to the lens status. For eyes with subluxated or dislocated crystalline lens, phacoemulsification cataract extraction or lens removal using an ocutome was performed. In eyes with a subluxated or dislocated IOL, the lifted-up IOL in the anterior chamber was cut in half using an IOL cutter and extracted through a clear corneal incision. SFIF-IOL was performed as previously described [6]. Because a 30G thin-wall needle used in the original study by Yamane et al. [6] was not available at our institute during the study period, a modified technique using a 26G needle was used [12]. Two 26G, bent, hollow needles were placed 180° apart and parallel to the limbus, 2 mm posterior to the limbus at the 3 o’clock and 9 o’clock positions. Through a clear corneal wound made by a 2.75-mm surgical keratome, a three-piece IOL (Sensar AR40e; AMO, Santa Ana, CA, USA) was inserted into the eye. Only eyes fixated with this IOL were included in this study. The leading haptic of IOL was docked with a needle and externalized. The end of the haptic was seared with high-temperature cautery, whereby the tip of the haptic shrivelled and curled up to form a flange. The flange of the haptic was then pushed back and fixed into the scleral tunnels. The same procedure was performed using the following haptic. Centring of IOL was checked.

Statistical analysis

Prediction error (PE) was calculated by subtracting the preoperative target refractive error from the postoperative achieved refractive error in the spherical equivalent. The Absolute Prediction error (APE) was defined as the absolute value of PE. PE and APE at the final follow-up were used for analysis. BCVA was converted to the logarithm of the minimum angle of resolution values for statistical analysis. The refractive surprise was defined as APE > +0.5 D. Univariable and multivariable logistic regression analyses were performed to determine factors associated with refractive surprise at the final visit, with calculation of odds ratios (ORs) and their 95% confidence intervals (CIs). Only variables with a P value of <0.1 in univariable analysis were included in the multivariable analysis. All statistical analyses were performed using R software (R version 4.2.1.; available at http://www.r-project.org; accessed December 2022). Continuous variables are presented as mean ± standard deviation. The level of statistical significance was set at P < 0.05.

Results

The medical records of 134 patients with 139 eyes subjected to SFIF-IOL were reviewed. From the 139 eyes, eight with concomitant surgery (glaucoma surgery, retinal surgery, corneal laceration repair, or penetrating keratoplasty), one with an unmeasurable AL, three that received IOLs other than the Sensar AR40E, eight with severe immediate postoperative complications requiring additional vitrectomy (IOL dislocation, n = 3; retinal detachment, n = 3; macular hole, n = 1, and postoperative endophthalmitis, n = 1), six with severe corneal decompensation requiring keratoplasty, and 22 without postoperative refraction data at ≥4 weeks after SFIF-IOL were excluded from the analysis. Finally, 91 eyes of 86 patients (25 female and 61 male patients) were included in the analysis. The mean age at the time of surgery was 62.4 ± 14.9 years (range, 16–85 years). The most common indication for SFIF-IOL was dislocation of IOL in the vitreous cavity (40 eyes, 44.0%). The mean AL was 25.0 ± 2.6 mm (range, 21.2–34.3 mm); 42 eyes (46.2%) showed AL < 24.0 mm while 23 eyes (25.3%) showed AL ≥ 26.0 mm. The baseline demographic and clinical characteristics are summarized in Table 1.

Table 1.

Baseline demographic and clinical characteristics of patients who underwent sutureless flanged intrascleral fixation of intraocular lens.

Variable	Value
Demographic characteristics
Patients/Eyes	86/91
Age at operation, years	62.4 ± 14.9
Sex, female/male	25/61
Clinical characteristics
Laterality, R/L	47/44
DM, n (%)	26 (30.2%)
HTN, n (%)	44 (51.2%)
AL, mm	25.0 ± 2.6
AL group
<24, n (%)	42 (46.2%)
24–26, n (%)	26 (28.6%)
≥26, n (%)	23 (25.3%)
Mean K, D	43.5 ± 1.7
CCT, μm	562.2 ± 52.8
Preop status
IOL dislocation, n (%)	40 (44.0%)
IOL subluxation, n (%)	18 (20.0%)
Phakia, n (%)	21 (23.1%)
Aphakia, n (%)	12 (13.0%)
Preoperative BCVA, logMAR (Snellen equivalent)	0.59 ± 0.64 (20/78)

DM diabetes mellitus, HTN hypertension, AL axial length, K Keratometry, D Dioptre, CCT central corneal thickness, IOL intraocular lens, BCVA best-corrected visual acuity, logMAR logarithm of the minimum angle of resolution, S.E. spherical equivalent, PE prediction error, APE absolute prediction error

Continuous data are presented as mean ± standard deviation.

The mean follow-up duration was 125.9 ± 194.0 days (range, 28–989 days). Eighty-one eyes (89.0%) were available for 4-week refraction assessments, and the mean PE and mean APE at 4 weeks were +0.01 ± 0.96 and +0.71 ± 0.65 D, respectively. Forty-four eyes (54.3%) showed refractive surprise, defined as APE > +0.5 D. At the final follow-up, the mean PE and APE were +0.07 ± 0.88 and +0.68 ± 0.56 D, respectively. Forty-nine eyes (53.8%) showed refractive surprise at the final visit. Univariable and multivariable logistic regression analyses showed that refractive surprise at the final visit was only associated with a shorter AL (OR, 0.825; 95% CI, 0.688–0.991; P = 0.039) at baseline (Table 2).

Table 2.

Postoperative refractive outcomes of patients who underwent sutureless flanged intrascleral fixation of intraocular lens.

Postoperative refractive outcome	All eyes	Short AL (<24 mm)	Moderate AL (24–26 mm)	Long AL (≥26 mm)	P value
Patients/Eyes	86/91	40/42	26/26	20/23
Follow-up duration, days	125.9 ± 194.0	126.6 ± 194.3	99.0 ± 138.7	155.2 ± 244.7	0.594
BCVA at final follow-up, logMAR (Snellen equivalent)	0.32 ± 0.51 (20/42)	0.47 ± 0.65 (20/59)	0.19 ± 0.33 (20/31)	0.19 ± 0.29 (20/31)	0.025*
S.E. at final follow-up, D	−0.58 ± 1.35	−0.11 ± 1.17	−0.72 ± 1.58	−1.29 ± 1.04	<0.001*
Astigmatism at final follow-up, D	−1.78 ± 1.10	−1.86 ± 1.19	−1.58 ± 1.01	−1.86 ± 1.05	0.445
PE at final follow-up, D	+0.07 ± 0.88	+0.10 ± 1.01	−0.01 ± 0.88	+0.09 ± 0.64	0.879
APE at final follow-up, D	+0.68 ± 0.56	+0.79 ± 0.62	+0.70 ± 0.51	+0.44 ± 0.46	0.014*

IOL intraocular lens, BCVA best-corrected visual acuity, logMAR logarithm of the minimum angle of resolution, S.E. spherical equivalent, PE prediction error, APE absolute prediction error

Continuous data are presented as mean ± standard deviation.

Statistical analysis was performed using the Kruskal–Wallis test.

^*indicates a significant difference (P < 0.05).

Figure 1 shows scatter plots of AL and refractive outcomes at the final visit. The correlation between AL and APE at the final visit, assessed using Spearman’s correlation analysis, was statistically significant (⍴ coefficient = −0.269, P = 0.010), while the correlation between AL and PE at the final visit was not significant (⍴ coefficient = −0.06, P = 0.530). For further analysis, the eyes were divided into three groups according to AL at baseline: short AL group (AL < 24 mm), medium AL group (24 mm ≤ AL < 26 mm), and long AL group (AL ≥ 26 mm). The postoperative refractive outcomes according to the AL are summarized in Table 3. There was no significant difference in PE among the three groups (P = 0.740; Kruskal–Wallis test). However, the long AL group showed lower APE than did the short AL and medium AL groups, and these differences were statistically significant (P = 0.021 compared with medium AL group; P = 0.0059 compared with short AL group; Mann–Whitney U test). There was no significant difference in APE between the medium and short AL groups. Figure 2 shows boxplots of PE and APE for patients stratified by the AL.

Fig. 1. Relationship between axial lengths and refractive outcomes.

Scatter plots of axial lengths and PE (A) and APE (B) values at the final visit of patients who underwent sutureless flanged intrascleral fixation of intraocular lens. PE prediction error, APE absolute prediction error.

Table 3.

Univariable and multivariable logistic regression analyses of risk factors for refractive surprise with absolute prediction error > 0.5 D after sutureless flanged intrascleral fixation of intraocular lens.

	Univariable			Multivariable
Variables	OR	95% CI	P	OR	95% CI	P
Age, years	1.014	(0.986, 1.043)	0.327
AL, mm	0.825	(0.688, 0.991)	0.039*	0.825	(0.688, 0.991)	0.039*
Mean K, D	1.291	(0.993, 1.679)	0.057
CCT, μm	1.001	(0.993, 1.009)	0.842
Targeted refraction, D	1.281	(0.836, 1.962)	0.256
Preop BCVA, LogMAR	0.951	(0.500, 1.812)	0.879

LogMAR logarithm of the minimum angle of resolution, BCVA best-corrected visual acuity, CI confidence interval, OR odds ratio, AL axial length, K keratometry, D dioptre, CCT central corneal thickness

^*indicates a significant difference (P < 0.05).

Fig. 2. Boxplots of axial length subgroups.

Comparison of PE (A) and APE (B) values according to the axial length in patients who underwent sutureless flanged intrascleral fixation of intraocular lens. PE prediction error, APE absolute prediction error.

Discussion

In the present study, we investigated the risk factors for PE after SFIF-IOL. APE showed a significant correlation with the AL; a longer AL was associated with a smaller APE. In the subgroup analysis according to the AL, eyes with AL ≥ 26.0 mm showed significantly smaller APE than did those with AL < 26.0 mm. To the best of our knowledge, this is the first study to investigate the ocular biometric factors associated with the refractive outcome of SFIF-IOL.

Previous studies have shown various results for PE after SFIF-IOL. Because there is no recommended A-constant for SFIF-IOL, surgeons have adopted the manufacturer’s recommended A-constant for an assumed in-the-bag IOL position; this could be a potential source of a less satisfactory refractive outcome after SFIF-IOL. According to the first report regarding the unique technique of SFIF-IOL published by Yamane et al., the mean postoperative shift was myopic (−0.21 ± 0.99 D) [6]. However, subsequent studies on IOL scleral fixation using this technique showed varied results in terms of the refractive outcome. Lee et al. reported a hyperopic shift with a mean refraction of +0.57 ± 1.27 D for variable fixation points at 1.5 to 2.5 mm from the limbus and +0.53 ± 1.18 D for fixation at 2.0 mm [11]. On the other hand, Rocke et al. reported no significant difference between the postoperative refraction and the in-the bag calculation (+0.04 ± 0.88 D) [9]. The present study also found no significant refractive shift from the in-the bag calculation (+0.07 ± 0.88 D). These findings suggest that use of the manufacturer’s recommended A-constant for an assumed in-the-bag IOL position for calculating the target refraction using the SRK-T formula for eyes subjected to SFIF-IOL could result in a favourable refractive outcome and is generally acceptable for SFIF-IOL.

In the present study, the mean APE for the total number of eyes at the final visit was +0.68 ± 0.56 D, which is comparable with those in previous studies. McMillin et al. reported a mean APE of +0.80 D at 3 to 4 weeks after the operation, while Kakisu et al. reported a mean APE of +0.89 D after a mean follow-up of 5.6 ± 9.5 months (range, 1–58 months) [10]. Rocke et al. reported a median APE of +0.50 D; however, they did not report the mean APE. According to the authors, the proportion of patients with PE ≤ 0.5 D was significantly lower with SFIF-IOL than with standard cataract surgery [9]. A greater deviation from the target refraction after SFIF-IOL may be associated with the absence of a unique A-constant for IOL power calculation. Moreover, because SFIF-IOL involves more delicate surgical procedures than does standard cataract surgery, thus resulting in a variable effective lens position (ELP), prediction of refraction may be less precise and will have greater potential error. Prediction of ELP in SFIF-IOL remains challenging, and various factors may affect the IOL position. The distance of fixation points from the limbus, length of the scleral tunnel, angle of hollow needle insertion at fixation points, amount of haptic shortening or cauterization, and ocular biometrics could contribute to ELP and determine the postoperative PE and APE after SFIF-IOL [13].

In the present study, a longer AL was associated with a smaller APE, whereas there was no significant correlation between AL and PE. In line with the present study, previous studies also reported very weak or no significant correlations between AL and PE [9, 13]. However, a significant association between AL and APE after SFIF-IOL has not been reported before. In our subgroup analysis according to the AL, long eyes (AL ≥ 26.0 mm) showed a significantly smaller mean APE than did medium-length eyes (AL 24.0–26.0 mm) and short eyes (AL < 24.0 mm). In previous reports, the mean APE after cataract surgery using in-the-bag IOL insertion in eyes with a long AL ranged from +0.407 to +0.550 D [14–16]. Considering that the mean APE in eyes with AL ≥ 26.0 mm was +0.44 ± 0.46 D in the present study, deviation from the target refraction in highly myopic eyes seems to be comparable between SFIF-IOL and standard cataract surgery using in-the-bag IOL insertion. However, the mean APE values of +0.79 ± 0.62 D for the short eyes and +0.70 ± 0.51 D for the medium-length eyes in the present study were greater than the reported mean APE after cataract surgery using in-the-bag IOL insertion, which ranged from +0.360 to +0.492 [14, 17]. Surgeons should be aware of refractive surprise in the short eyes and medium-length eyes although the PEs of them were not statistically different from the long eyes. The SRK-T formula using the manufacturer’s recommended A-constant should be considered as the first option for prediction of postoperative refraction regardless of the AL range.

The mechanism underlying the association between a longer AL and a smaller APE after SFIF-IOL in the present study remains unclear, although this finding is in line with those of previous studies wherein the accuracy of the SRK-T formula for IOL power calculation in standard cataract surgery was greater for eyes with a longer AL than for those with a shorter AL [17, 18]. In addition, although ELP can be affected by various factors during SFIF-IOL, the postoperative refractive error caused by changes in ELP is strongly dependent on AL. In an actual large dataset, the postoperative PE resulting from the same amount of error in ELP showed a gradual decrease with an increase in AL; this suggests that ELP prediction remains much more important for short eyes [19]. However, the present study did not evaluate anterior optical coherence tomography (OCT) images, and further studies utilizing anterior OCT should elucidate the association between AL and the position of the implanted IOL.

The present study has several limitations. First, approximately 16% eyes were excluded from the analysis due to the lack of postoperative refraction data at ≥4 weeks after surgery. Considering the retrospective study design, there may have been some bias in those eyes. Second, due to the retrospective nature of the study design, we did not have anterior segment OCT to determine the position of the implanted IOL. Therefore, the degree of IOL tilt or decentration could not be measured in the analysis. However, we excluded eyes with severe postoperative IOL tilt or subluxation that required additional surgery. As the extent of IOL tilt and the degree of decentration may influence the postoperative refractive outcome in SFIF-IOL, further studies are needed to investigate the relationship between the actual position of IOL using anterior segment OCT, and the postoperative refractive outcomes. Third, the results cannot be generalized to the other methods of scleral fixated IOL. As the technique used in the study includes the searing with high-temperature cautery and forming a flange, it might have influenced the length of haptics. The refractive outcomes in sutured scleral fixation or scleral fixation using fibrin glue may differ from our results. Fourth, only one type of three-piece IOL was used in the present study, and the results may not be applicable to other IOLs. However, we could exclude the possible influence of the IOL type on prediction of the refractive error after SFIF-IOL, which could be a strength of the present study.

In conclusion, the refractive outcome after SFIF-IOL using the manufacturer’s recommended A-constant for in-the-bag IOL insertion was favourable regardless of the AL range. However, the absolute value of deviation from the target refraction was > +0.5 D on average, and it was large enough to result in unexpected postoperative refractive outcomes for some eyes. Eyes with a longer AL were more likely to show a smaller deviation from the target refraction; further investigations are required to verify this finding and elucidate the underlying mechanism.

Summary

What was known before

• Refractive outcomes after sutureless flanged intrascleral fixation of intraocular lens have been inconsistent.

• Some studies reported myopic refractive error shifts while others showed mean prediction errors that indicated emmetropia or hyperopia.

What this study adds

• The refractive outcome after sutureless flanged intrascleral fixation of intraocular lens (IOL) using the manufacturer’s recommended A-constant for in-the-bag IOL insertion was favourable

• Eyes with a longer axial length were more likely to show a smaller deviation from the target refraction.

Author contributions

R.O. acquired and analysed the data, drafted the initial manuscript, and revised the manuscript. K.B., C.K.Y. conceptualized and designed the study, and collected data. C.H.Y. critically reviewed the manuscript. U.C.P., E.K.L. conceptualized and designed the study, coordinated and supervised data collection, analysed the data, critically reviewed the manuscript, and revised the manuscript. All authors read and approved the final manuscript.

Funding

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (Information and Communication Technology, NRF-2021R1F1A1045417).

Data availability

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Competing interests

The authors declare no competing interests.