FormalPara Key Summary Points

Why carry out this study?

Combined phacovitrectomy has been established as safe and effective in reducing patient burden. However, depending on the surgical technique, refractive errors can be a problem.

In this study, using the latest intraocular lens (IOL) calculation formula and standardizing the surgeon and intraocular lenses used, we examined the outcomes of isolated cataract surgery, combined phacovitrectomy and cataract surgery, and vitrectomy with gas injection.

What was learned from the study?

This study revealed that simultaneous combined phacovitrectomy using gas produces a significant postoperative myopia error.

This myopia error was found to be related to the anterior shift in the IOL. To minimize postoperative refractive error, it is recommended that approximately +0.5 to 0.8 D should be added to the predicted refraction value.

In addition, it has been suggested that the Barrett Universal II formula may be the most accurate formula, but no statistically significant differences have been identified.

Introduction

Phacovitrectomy, which is the combination of phacoemulsification, pars plana vitrectomy (PPV), and intraocular lens (IOL) implantation, has become increasingly popular over the past few years for the treatment of vitreoretinal disorders [1,2,3,4]. Considering that up to 80% of eyes develop nuclear sclerotic cataract within 2 years after PPV [5], and given the higher complication rates of phacoemulsification in eyes having vitrectomy [6], a combined surgical procedure is being considered even in the absence of a significant cataract. Furthermore, a single surgery has several advantages over a combined surgery in terms of improved retina visualization, faster visual acuity recovery, safer vitreous shaving without concerns about intraoperative lenticular touch, and lower cost [7].

In eyes with rhegmatogenous retinal detachment (RRD), postoperative myopic shift may occur because of the possible errors in axial length measurement and forward movement of the IOL position due to gas tamponade [8, 9]. Forward fixation of the IOL caused myopic refractive errors using anterior segment optical coherence tomography (AS-OCT) even after the gas had disappeared in eyes undergoing phacovitrectomy with gas tamponade [10]. The achievement of a target refractive outcome has become increasingly essential since patients’ refractive expectations are increasing and the technology is well advanced. However, at present, IOL power calculations are usually performed without any adjustments considering the added vitrectomy. This may account for the reported mixed results, some of them revealing a lower accuracy of refractive predictions in such patients, compared with phacoemulsification alone [11].

To the best of our knowledge, there has been only one recently published article comparing formula accuracy in phacovitrectomized eyes with and without gas tamponade [10]. However, previous studies have not standardized the surgeon, the IOL, or vitrectomy technique, which may have resulted in variations in the refractive index and the postoperative shape of the eye. Furthermore, we have found no precedent studies using different state-of-the-art IOL formulas. This study aims to evaluate refractive error after phacovitrectomy with and without the use of gas tamponade, especially when we unify the surgeon, the implanted IOL, and surgical techniques.

Methods

Study Population

We retrospectively conducted a clinical chart review of consecutive patients who had undergone cataract surgery or phacovitrectomy between December 2021 and April 2022 at Kozawa Eye Hospital and Diabetes Center. The study adhered to the principles of the Declaration of Helsinki. This study was approved by the Institutional Review Board at the Kozawa Eye Hospital and Diabetes Center, Ibaraki, Japan (KG2021-15).

Inclusion and Exclusion Criteria

Eligible patients were classified into the three groups: Group 1, uneventful phacoemulsification with spherical hydrophobic monofocal in-the-bag IOL insertion; Group 2, uneventful combined phacovitrectomy for epiretinal membrane (ERM), with spherical hydrophobic monofocal in-the-bag IOL insertion; Group 3, uneventful combined phacovitrectomy for macular-on RRD, with spherical hydrophobic monofocal in-the-bag IOL insertion. Intravitreal injection of 20% SF6 endotamponade was applied in all cases of Group 3.

Exclusion criteria were as follows: incomplete biometry data, postoperative corrected visual acuity < 20/50, corneal astigmatism > 3 diopters (D), any intraoperative or postoperative complication, any history of eye surgery or ocular trauma, or any concomitant eye disease. Phacovitrectomies were conducted for symptomatic patients (decreased visual acuity or metamorphopsia) due to any vitreomacular interface disease (ERM, vitreomacular traction, and full-thickness macular hole).

Surgical Technique

All surgeries were performed by a single experienced surgeon (Y.T.). In all cases, cataract surgery was performed with phacoemulsification through a 2.2-mm clear corneal incision with a Centurion unit (Alcon Laboratories, Inc, Fort Worth, TX, USA). The IOL was implanted into the capsular bag with subsequent three-piece IOL insertion (NX-70S, Eternity Fine Natural®, optical zone 7.0 mm; Santen Pharmaceutical Co., Ltd., Osaka, Japan). In Group 2, after cataract surgery, a 25-gauge pars plana vitrectomy was performed under local anesthesia with the Constellation Vision System (Alcon Laboratories, Inc, Fort Worth, TX, USA). Posterior vitreous detachment was confirmed with triamcinolone acetonide including core vitrectomy, posterior vitrectomy, and vitreous base shaving with scleral depression. Brilliant blue dye and a 25-gauge Grieshaber Revolution® DSP forceps (Alcon Laboratories, Geneva, Switzerland) were applied to peel the internal limiting membrane (ILM) for ERM. The ILM was removed in a circular fashion up to the temporal arcade and to the optic disk. No gas tamponade was performed in Group 2. In Group 3, after cataract surgery, a 25-gauge pars plana vitrectomy was performed under local anesthesia in eyes with RRD. After removal of the core and peripheral vitreous, posterior vitreous detachment was created if needed, and residual of the posterior vitreous cortex adhered to the retina was removed with the aid of triamcinolone acetonide. The peripheral vitreous base was shaved in all cases using a vitrectomy probe under scleral depression. After complete release of traction on retinal tears, the retina was flattened by either injection of perfluorocarbon liquid or fluid-to-air exchange, and the subretinal fluid was extracted from the primary breaks in all cases. Then, retinal breaks were cured by endolaser photocoagulation, and the vitreous cavity was replaced with 20% sulfur hexafluoride (SF6). Patients undergoing gas tamponade were advised to maintain a lateral position for 1 day to 1 week.

Biometry

Preoperatively, patients underwent a complete ophthalmological examination, including OCT of the posterior segment (DRI OCT Triton; Topcon, Tokyo, Japan), to diagnose ERM or macular-on RRD. Optical biometry was performed with a swept-source (SS)-OCT device (ARGOS, Alcon Laboratories, Inc.), obtaining the following data for each patient: axial length (AL), anterior chamber depth (ACD), central corneal thickness (CT), keratometry (K), lens thickness (LT), and horizontal corneal diameter. Postoperative manifest refraction was assessed at 3 months after surgery.

We also evaluated the change in IOL position using SS-OCT (CASIA2, Tomey, Nagoya, Japan). The distance from the central corneal endothelial surface to the center of the crystalline lens thickness was measured preoperatively (A). The distance from the central corneal endothelial surface to the anterior surface of the IOL was measured 3 months following surgery (B). The change in IOL position was defined as the difference between those values (A − B). A positive value of the change in IOL represents movement forward to the corneal endothelium.

Intraocular Lens Calculations

The Barrett Universal II formula was used to evaluate the refractive outcomes for the comparison among the three groups. Four IOL power calculation formulas were obtained, using a keratometric index of 1.3375. The SRK/T, Hill–radial basis function (RBF) version 3.0, Kane, and Barrett Universal II formulas were calculated using a newly released platform. A constant (119.6) was applied for SRK/T and Hill-RBF and Kane formulas. The recommended lens constant for cataract surgery was used for the Barrett Universal II (2.20).

Outcome Measurements

We measured visual acuity using a decimal acuity chart of Landolt rings at 5 m under bright light conditions (500 lx). After we obtained objective refractions using an autorefractometer (MR-6000, Tomey, Nagoya, Japan), the results were referenced as a starting point for a full manifest refraction. We subjectively determined the astigmatic power and axis using the cross-cylinder method under monocular conditions. The primary outcome, refraction prediction error, was calculated as the difference between the spherical equivalent of the subjective refraction and the calculated prediction error. A negative refractive prediction error means a myopic result, and a positive prediction error represents a hyperopic outcome [12]. Study outcome measures included the mean prediction error (MPE) and its standard deviation (SD), and the mean absolute error (MAE) and median absolute error (MedAE) for each formula, following Wang et al. [12] and Sánchez-González et al. [13] recommendations. We compared the predictability outcomes using the four formulas among the three groups. For subgroup analysis, we also compared the predictability outcomes in eyes with normal axial length (≤ 26 mm) and eyes with long axial length (> 26 mm) using the four formulas.

Statistical Analysis

Statistical analyses were performed with SAS [Statistical Analysis Software] (version 9.4; SAS Institute, Cary, NC, USA). The outcome measures were expressed as the mean ± standard deviation. The one-way analysis of variance (ANOVA) test was used to compare the parameters among the three groups and those using the four formulas, with the Tukey test being employed for multiple comparisons. The Mann–Whitney U test was used to compare between the two groups. The association between the MPE and the change in IOL position was evaluated by Spearman’s correlation coefficient based on the non-normally distributed data.

For sample size calculation, the PS program (version 3.0.12; Dupont WD, Plummer WD Jr. PS: Power and Sample Size Calculation, version 3.0. Department of Biostatistics, Vanderbilt University, Nashville, TN, USA) was utilized. It was estimated that a sample size of 97 eyes would be required to identify a difference of one third of the SD of differences in the prediction error, with a significance level of 5% and a test power of 90%.

Results

A total of 104 eyes were included (Group 1: 30; Group 2: 34; Group 3: 40) in the current study. In Group 2, all eyes had the diagnosis of ERM preoperatively. In Group 3, all had macular-on RRD, and SF6 gas was injected into the vitreous cavity. Patients’ biometric data, by group, are presented in Table 1. There was no statistically significant difference regarding AL, ACD, mean keratometry, or IOL power between Group 1 and Group 2. As for age and LT, significant differences were found.

Table 1 Demographic and biometric data of patients in each group
Full size table

Postoperative refractive errors based on the Barrett Universal II formula are summarized in Table 2. Comparing MPE among the three groups, a significant difference was found using one-way ANOVA (P < 0.01). MPEs were significantly different in Groups 1 and 2 relative to Group 3 (Tukey test, P < 0.01, P < 0.01). The MAE also differed significantly among the three groups (P < 0.01). MAEs were significantly different in Groups 1 and 2 relative to Group 3 (Tukey test, P < 0.01, P < 0.01). The boxplots of MPE and MAE in the three groups are shown in Fig. 1. The change in IOL position differed significantly among the three groups (P < 0.01). There was a significant difference in IOL position change between Group 1 and Group 2 relative to Group 3 (Tukey test, P < 0.01, P < 0.01).

Table 2 Refractive errors using the Barrett Universal II formula and the change in IOL position at 3 months in each group
Full size table
Fig. 1
figure 1

Boxplot of A prediction and B absolute error in the three groups

Full size image

In Group 3, the linear regression function was not significant between the MPE and the change in IOL position (r = −0.043, P = 0.79) (Fig. 2).

Fig. 2
figure 2

Scatterplots showing the association between mean absolute error and change in intraocular lens position in Group 3

Full size image

The comparison of refractive errors among the four formulas is summarized in Table 3. In all groups, there were no significant differences in MPE and MAE when using any of the four formulas.

Table 3 Comparison of refractive errors among the four formulas in each group
Full size table

The predictability outcomes of eyes with normal axial length and eyes with long axial length are shown in Table 4. Hill-RBF showed a significant myopic shift in eyes with long axial length in Groups 1 to 3. The Kane and Barrett Universal II formulas also showed a significant myopic shift in eyes with long axial length in Group 1. Otherwise, we found no significant differences between the two groups in terms of MPE or MAE when using the four formulas.

Table 4 Refractive error using the four formulas based on the axial length in each group
Full size table

Discussion

In this study, we compared the refractive outcomes and the change in IOL position in three groups: cataract surgery group (Group 1), vitrectomy for ERM without gas tamponade group (Group 2), and vitrectomy for RRD with gas tamponade group (Group 3). The MPE at 3 months after surgery was −0.08 ± 0.37 D in Group 1, −0.26 ± 0.32 D in Group 2, and −0.59 ± 0.34 D in Group 3. Group 3 showed significantly more myopic changes than other groups. The change in the IOL position was significantly more anterior in Group 3 than in Groups 1 and 2. The vitreous cavity was completely filled with SF6 gas at the end of surgery in Group 3 in all patients with RRD. We speculate that the enforcement of prone and lateral position under 20% SF6 gas might have induced the IOL forward shift, resulting in a significant postoperative myopic shift. Shiraki et al. [10] also reported that myopic shift after vitrectomy with gas tamponade is because the buoyancy and surface tension of the gas pushed the IOL after the vitrectomy with the gas tamponade procedure, even if the patients maintained a strict prone position.

Previous studies on refractive errors after phacovitrectomy for RRD with gas tamponade are summarized in Table 5, ranging from 0.16D to −0.82D, with most previous studies showing myopic migration. In particular, Shiraki et al. [10] found −0.82 ± 0.64 D using the Barrett Universal II formula, and Cho et al. [15] found −0.40 ± 0.67 D using the SRK/T formula, both of which are consistent with our results. Shiraki et al. [10] also investigated the correlation between the anterior shift in the IOL position and MPE at 1 month in vitrectomy with gas tamponade for patients with a macular hole and RRD. However, in the current study, we found no significant correlation between MPE and change in IOL position at 3 months. This discrepancy may have resulted from the differences in the follow-up period as well as macular pathology. In the present study, the myopic shift of −0.51 D to −0.78 D led us to consider modifying the IOL power calculation to further improve the postoperative refractive outcomes in patients with RRD requiring phacovitrectomy with gas tamponade. The addition of approximately +0.5 to 0.8 D to the preoperative predicted refractive power may be recommended when selecting IOL power in such patients.

Table 5 Comparison of refractive error after phacovitrectomy with gas in previously studies
Full size table

We compared the accuracy of IOL formulas in 25-gauge phacovitrectomy for macular-on RRD with gas tamponade. Although the Barrett Universal II formula showed the lowest MPE and MAE in the four formulas, no significant differences existed. In 25-gauge phacovitrectomy without gas tamponade for ERM, Sato et al. [18] compared the accuracy of IOL power calculations using 10 IOL formulas, including new and conventional formulas, and stated that the Barrett Universal II formula showed the lowest standard deviation, MPE, and MAE, in addition to achieving the highest percentage of eyes with a refractive prediction error within ± 0.25 D. We assume that the Barrett Universal II formula is most preferable for calculating IOL power in phacovitrectomy.

This study has at least two limitations. Firstly, the study included a retrospective design, a relatively small sample size, and a short study period. However, the sample size calculation addressed the 90% of test power. This study confirmed that the postoperative myopic shift was significantly greater in the RRD group than in the cataract and ERM groups. Our findings are clinically helpful for improving our understanding of the postoperative IOL position after surgery and minimizing refractive errors in phacovitrectomy with gas tamponade. Secondly, we applied only a single IOL model, and differences in IOL design could affect refractive MPE. Therefore, we cannot generalize the results of this study to patients assessed using different IOL models. However, the data from phacovitrectomies performed by an experienced surgeon for relatively uniform RRD is clinically valuable for predicting postoperative refractive outcomes.

Conclusions

In conclusion, the postoperative myopic shift was significantly higher in the RRD group. The myopic shift should be taken into consideration to obtain better refractive outcomes in eyes with RRD. The Barrett Universal II formula may be preferable for calculating IOL power in eyes with phacovitrectomy for RRD.