Comparison of Two Techniques in Phacoemulsification: Hydroimplantation and Viscoimplantation

Abstract

Objectives

The aim of this study was to compare hydroimplantation and viscoimplantation techniques in phacoemulsification surgery by analyzing corneal tomography parameters and changes in intraocular pressure (IOP).

Methods

This retrospective study included 74 eyes of 74 consecutive patients who underwent phacoemulsification surgery and implantation of a foldable intraocular lens (IOL). Each eye was assigned to either the viscoelastic material (VEM) group (VEM(+); (n=39) or the VEM (–) group (n=35). Accordingly, IOL implantation was performed with VEM (1.4% sodium hyaluronate; Protectalon, VSY, Turkey) in the VEM(+) group, whereas hydroimplantation without VEM was used in the VEM (–) group. Post-operative examinations were performed on post-operative days 1, 3, and 7, and at 1 month.

Results

There was no statistically significant difference in IOP between the VEM(+) and VEM(–) groups before surgery or at any post-operative time point except at 24 h. At 24 h postoperatively, the VEM(+) group had a significantly higher IOP compared to the VEM(–) group (p=0.010). In addition, the central corneal thickness at 1 month was significantly higher in the VEM(+) group than in the VEM(–) group (p=0.027). No statistically significant differences were found between the groups in best corrected visual acuity, anterior chamber depth, and axial length. There was no posterior capsule rupture or zonular dialysis in either group.

Conclusion

Phacoemulsification using the hydroimplantation technique appears to be a safe and feasible approach that may help mitigate early post-operative IOP elevation; however, assessing corneal endothelial cell function by specular microscopy would be important for a more comprehensive safety comparison between techniques.

Introduction

Cataract surgery is the most common operative procedure performed by ophthalmologists. This operation is predominantly performed using the modern technique of phacoemulsification combined with intraocular lens (IOL) implantation (1). During the IOL implantation stage of phacoemulsification, viscoelastic material (VEM) is routinely employed. However, several reports have indicated that VEM remaining in the anterior chamber (AC) cannot be completely removed using the irrigation-aspiration system following the application of VEM during IOL implantation (2,3).

Recent studies have described a hydroimplantation technique for IOL implantation that eliminates the need for VEM (4,5). In this approach, the irrigation cannula is introduced into the AC through the lateral port, while the injector is maneuvered through the main incision (6,7). As no VEM is used during the procedure, there is no risk of residual substance remaining in the capsular bag. Furthermore, this technique is regarded as both simple and safe, particularly as the irrigation cannula provides additional ocular stability when introduced through the lateral port.

Previous studies have compared pre- and post-operative central corneal thickness (CCT) and intraocular pressure (IOP) values between the viscoimplantation and hydroimplantation groups; however, differences in AC depth (ACD) on days 1, 3 and 7, as well as at 1 month, were not compared between the two groups (8,9).

In this study, we investigated the effects of IOL implantation performed with or without VEM on post-operative measurements, including IOP, corneal curvature (K1: flat meridian, K2: steep meridian), ACD, and CCT.

Methods

Study Design and Ethics

This retrospective study included 74 eyes of 74 patients who underwent standard phacoemulsification with foldable IOL implantation at the Department of Ophthalmology, Akdeniz University, Antalya, Türkiye, between November 2016 and January 2017. The study was conducted in accordance with the Declaration of Helsinki and approved by the institutional ethics committee of Akdeniz University (KAEK 20 No:77). Written informed consent was obtained from all participants before surgery.

Participants

Eligible participants were patients with nuclear age-related cataract up to Grade 2 according to the Lens Opacity Classification System III, without additional ocular diseases (10). Exclusion criteria included a history of ocular trauma or surgery, lens subluxation, zonular weakness, complicated cataract, degenerative myopia, uveitis, corneal endothelial pathologies such as Fuchs’ endothelial dystrophy, and clinically evident pseudoexfoliation syndrome.

Pre-operative Evaluation

All patients underwent a comprehensive ophthalmological examination, including assessment of best corrected visual acuity (BCVA) with a Snellen chart (converted to LogMAR), assessment of the anterior and posterior segment of the eye, and measurement of IOP with non-contact tonometry (CT-80, Topcon, Japan). Corneal curvature (K1, K2), ACD and CCT were measured with a corneal topography system (Pentacam HR, Oculus, Germany). The axial length (AL) and the corneal curvature for the calculation of the IOL power were determined with the IOLMaster 500 (Carl Zeiss Meditec, Germany).

Randomization and Surgical Technique

The patients were randomly divided into two groups: The viscoimplantation group (VEM+) and the hydroimplantation group (VEM–). Group allocation was determined using a computer-generated table of random numbers to ensure unbiased distribution. All surgical procedures were performed by two experienced surgeons (M.Ü. and H.D.İ.) under topical anaesthesia with proparacaine hydrochloride (Alcon, Switzerland), utilizing the same phacoemulsification platform (Infinity Vision System, Alcon, USA). To minimize variability between surgeons, each surgeon performed the same number of procedures in both groups.

Standard main and secondary corneal incisions were performed using 20 G MVR knives, and the AC was filled with dispersive (Viscoat, Alcon, USA) and cohesive (Protectalon, VSY, Turkey) VEM. A continuous curvilinear capsulorhexis approximately 0.5 mm smaller than the IOL optic diameter was performed, followed by hydrodissection and hydrodelineation. The nucleus was removed using the stop-and-chop technique, and the residual cortical material was aspirated with bimanual irrigation/aspiration.

In the VEM(+) group, the capsular bag was filled with viscoelastic before IOL implantation, whereas in the VEM(–) group, IOL implantation was performed under continuous irrigation without the use of VEM. When VEM was employed, it was thoroughly aspirated at the end of the procedure. The wounds were sealed by stromal hydration, and 0.1 cc of intracameral moxifloxacin was administered; no sutures were required. Postoperatively, all patients received topical antibiotic drops 4 times daily for 1 week and topical corticosteroids 4 times daily for 1 week, which were subsequently tapered over a 4 weeks period.

Post-operative Follow-up and Measurements

Post-operative evaluations included IOP, ACD, AL, CCT, corneal curvature (K1, K2), refraction, and BCVA (LogMAR). Measurements were obtained on post-operative days 1, 3, and 7, and at 1 month. The ACD, CCT, and corneal curvature were measured using the Scheimpflug imaging system (Pentacam HR, Oculus, Germany). These follow-up intervals were specifically selected to reflect our routine post-operative schedule for patients undergoing phacoemulsification and are optimal for detecting early alterations in the anterior segment. Similar intervals have been reported in previous studies, e.g. by Cho (11), Sallam and Zaky and Zhu et al., (12) who investigated early post-operative AC dynamics, IOP fluctuations and endothelial outcomes after cataract surgery.

Statistical Analysis

Data were analyzed using the Statistical Package for the Social Sciences (SPSS) version 22.0 (SPSS Inc., Chicago, IL, USA) and Statistical Analysis System (SAS) version 9.4 (SAS Institute, Cary, NC, USA). Normality was assessed with the Shapiro–Wilk test. Continuous variables are summarized as mean±standard deviation when approximately normal and as median when non-normal. Between-group comparisons used the independent-samples t test or the Mann–Whitney U test, respectively. For repeated measurements over time, repeated-measures Analysis of Variance was applied when assumptions were met (sphericity assessed by Mauchly’s test with Greenhouse–Geisser correction when violated); otherwise, the Friedman test (with Wilcoxon signed-rank tests for post hoc comparisons) was used. Categorical variables were compared using Fisher’s exact test. Effect sizes were reported as Hedges’ g (or Cohen’s d) for parametric contrasts and as the Hodges–Lehmann median difference with 95% confidence intervals for non-parametric contrasts. The primary endpoint was post-operative day-1 IOP. In addition, the proportion of eyes with IOP >30 mmHg on day 1 was analyzed as a clinically relevant binary outcome (risk ratio with 95% confidence interval; Fisher’s exact p value). No formal multiplicity correction was applied to secondary or exploratory analyses; the primary endpoint was prespecified a priori. Two-sided p<0.05 was considered statistically significant.

Results

A total of 74 eyes of 74 patients were included in the study, of which 39 patients were in the viscoimplantation group (VEM+) and 35 in the hydroimplantation group (VEM–). The demographic characteristics and cataract grading of the groups are summarized in Table 1. There were no statistically significant differences between the groups in terms of age, gender distribution or cataract grade. No intraoperative complications were observed in either group.

Table 1.

Comparison of demographic and clinical characteristics between the VEM(+) and VEM(–) groups

	VEM				All		X2	P
	VEM(+)		VEM(-)
	n	% (mean)	n	% (mean)	n	% (mean)
Age (years)	39	52.70 (66.38)	35	47.30 (68.31)	75	(67.54)	0.231	0.821
Eye							0.043	0.835
Right eye	18	46.15	17	48.57	35	47.30
Left eye	21	53.85	18	51.43	39	52.70
Sex							0.711	0.399
Female	13	33.33	15	42.68	28	37.84
Male	26	66.67	20	57.14	46	62.16
PAMC							6.728	0.081
0	29	74.36	33	94.29	62	83.78
1	4	10.26	2	5.71	6	8.11
2	4	10.26			4	5.41
3	2	5.13			2	2.70
LOS (NO2)					5.572	0.233
2	5	12.82	4	1 1.43	9	12.16
3	6	15.38	1	2.86	7	9.46
4	16	41.03	13	37.14	29	39.19
5	8	20.51	14	40.00	22	29.73
6	4	10.26	3	8.57	7	9.46

Categorical variables were compared using the Chi-square (X²) test. Data are presented as number (n) and percentage (%), and P<0.05 were considered statistically significant. PAMC: Post-operation antiglaucoma medication count, LOS: Lens opacification system, VEM: Viscoelastic material, VEM(+): Group of viscoimplantation, VEM(-): Group of hydroimplantation.

Table 2 shows BCVA, IOP, CCT, corneal curvature values (K1, K2), ACD, AL, IOL power, and P-values of patients before and after surgery (Figs. 1-3). There was no difference between the groups in terms of BCVA before and after surgery (p=0.241 and p=0.426, respectively). Distributional checks indicated that day-1 IOP in the VEM(+) group deviated from normality; therefore, non-parametric testing was used for this endpoint. There were no between-group differences in IOP at baseline or at post-operative day 3, day 7, or month 1 (p=0.097, 0.147, 0.106, and 0.781, respectively) (Fig. 4). On day 1, IOP was higher in the VEM(+) than in the VEM(–) group (Mann–Whitney U, two-sided p=0.003). The proportion of eyes with IOP >30 mmHg on day 1 was 13/39 (33.3%) in VEM(+) versus 2/35 (5.7%) in VEM(–), risk ratio 5.83 (95% CI 1.41–24.06); Fisher’s exact p = 0.003. All spikes were managed with systemic acetazolamide. There was no significant difference in pre-operative CCT between the two groups (p=0.377); however, CCT was significantly higher in the VEM(+) group than in the VEM(–) group 1 month postoperatively (p=0.027).

Table 2.

Comparison of ocular parameters, including BCVA, IOP, corneal, and anterior chamber measurements, between the VEM(+) and VEM(–) groups

	VEM(+) group (n=39)	VEM(-) group (n=35)	P
VA (pre-operative, LogMAR)	0.90±0.54	0.75±0.49	0.241
VA (post-operative 1M, LogMAR)	0.08±0.13	0.12±0.27	0.426
IOP (pre-operative, mmHg)	18.13±3.13 (10-24)	19.26±2.59 (14-24)	0.097
IOP (post-operative 1d, mmHg)	22.05±5.92 (13-33)	18.74±4.68 (13-35)	0.003
IOP (post-operative 3d, mmHg)	16.87±2.52 (9-20)	16.06±2.24 (11-20)	0.147
IOP (post-operative 7d, mmHg)	17.10±2.14 (13-21)	16.26±2.31 (11-20)	0.106
IOP (post-operative 1M, mmHg)	16.82±2.44 (12-23)	16.97±2.19 (12-20)	0.781
IOL Power (D)	20.95±3.71	21.09±2.14	0.848
AL (pre-operative, mm)	23.57±1.70	23.42±0.89	0.643
K1 (pre-operative, D)	43.39±1.57	43.31±1.47	0.826
K1 (post-operative 1M, D)	43.10±1.69	43.14±1.64	0.942
K2 (pre-operative, D)	44.18±1.61	44.20±1.62	0.969
K2 (post-operative 1M, D)	44.14±1.59	44.07±1.57	0.853
ACD (pre-operative, mm)	3.13±0.47	3.22±0.36	0.334
ACD (post-operativeId, mm)	3.54±0.56	3.58±0.46	0.788
ACD (post-operative 3d, mm)	3.76±0.42	3.72±0.35	0.677
ACD (post-operative 7d, mm)	3.76±0.35	3.84±0.25	0.293
ACD (postop 1M, mmHg)	3.82±0.32	3.87±0.26	0.480
CCT (pre-operative, μm)	542.26±35.30	534.29±41.84	0.377
CCT (post-operative 1M, μm)	549.49±30.33	531.20±39.34	0.027

Statistically significant P-values are shown in bold.Values are presented as mean±SD (min–max).VEM:Viscoelastic material, VEM(+): Group of viscoimplantation, VEM(–): Group of hydroimplantation, VA:Visual acuity, logMAR: Logarithm of the minimum angle of resolution, pre-operative: Pre-operative, IOP: Intraocular pressure, mmHg: Millimeters of mercury, post-operative 1d: Post-operative day 1, post-operative 3d: Post-operative day 3, post-operative 7d: Post-operative day 7, post-operative IM: Post-operative month 1, IOL: Intraocular lens, D: Diopter, AL: Axial length, mm: Millimeter, K1: Flat keratometry, K2: Steep keratometry, ACD: Anterior chamber depth, CCT: Central corneal thickness, μm: Micrometer, SD: Standard deviation, min: Minimum, max: Maximum.

Figure 1.

Anterior chamber depth-time changes.

Figure 3.

Central corneal thickness-time changes.

Figure 4.

Intraocular pressure-time changes.

Figure 2.

Anterior chamber depth-time changes.

Discussion

VEM are used in cataract surgery to preserve the AC, protect intraocular tissues from ultrasound energy, maintain intraoperative ocular tone, and facilitate IOL implantation (1,2). An optimal VEM should be readily removable from the AC at the end of surgery, as any residual material may elevate IOP, induce intraocular inflammation, and potentially damage the corneal endothelium (3). Although the VEM is removed during the irrigation/aspiration phase after IOL implantation, it may remain slightly behind the IOL. Complications such as posterior capsule rupture may also occur while the VEM remains behind the IOL (13). In addition, the VEM between the IOL and the posterior capsule may lead to capsular block syndrome after surgery, and myopic shift may develop due to the displacement of the IOL in the capsular bag (14).

In 2010, Tak et al. (4) described the hydroimplantation method for IOL implantation in response to the potential adverse effects of viscoelastic agents. Hydroimplantation offers several advantages, including reduced surgical time and facilitated IOL implantation by stabilizing the eyeball with the irrigation cannula. Moreover, the improved adhesion between the IOL and the posterior capsule may help prevent posterior capsule opacification by limiting the migration of equatorial epithelial cells towards the central capsule. Although several studies have reported on this technique, no study has compared post-operative ACD and corneal curvature values with the Pentacam system.

In our study, the patients were divided into two groups: VEM(+) and VEM(–), and the post-operative values of ACD, IOP, CCT and corneal curvature (K1, K2) were compared. The post-operative IOP on day 1 was significantly higher in the VEM(+) group than in the VEM(–) group. Elevated IOP in the post-operative period is clinically important, particularly in individuals who are vulnerable to optic nerve injury (15,16). In our study, there were no cases with glaucoma or pseudoexfoliation. The most common cause of an early increase in IOP after cataract surgery is blockage of viscoelastic-induced trabecular flow in the AC (17-20). When comparing the VEM(+) and VEM(–) groups, IOP was significantly higher in the VEM(+) group only on the 1st post-operative day. Although the difference was not statistically significant, patients in the VEM(+) group were more likely to require post-operative antiglaucoma medication (Table 1). Overall, the higher incidence of IOP spikes on post-operative day 1 in the VEM(+) group likely reflects a multifactorial process rather than a single mechanism. A plausible contributor is residual VEM despite careful aspiration. Small amounts may remain in the AC angle and transiently impede aqueous humor outflow. This mechanism is well documented, particularly with dispersive ophthalmic viscosurgical devices such as Viscoat and with soft shell techniques (21). In addition, the VEM(+) group had a slightly longer mean AL. Although this difference was not statistically significant, prior studies suggest that greater AL may predispose eyes to transient IOP elevation (22). Post-operative inflammation may also contribute. We did not measure inflammatory markers in this study, which we acknowledge as a limitation. Finally, interindividual variation in steroid responsiveness could have played a role (23). In addition, it is possible that some patients in the VEM(+) group did not strictly adhere to their post-operative medication regimen, which may have contributed to higher IOP levels; the lack of objective verification of patient compliance is another limitation of our study. A less likely explanation is that this finding was incidental in this group or that some patients squeezed their eyes during tonometry, resulting in artifactually elevated measurements. Given the relatively small cohort size, such confounding may occur, and larger prospective studies with longer follow-up are needed to confirm these findings. No difference in IOP measurements was observed at post-operative day 3 follow-up.

While previous studies generally reported no significant difference in pre- and post-operative CCT between the groups, we observed a significantly thicker CCT in the VEM(+) group at 1 month. This may be explained by several mechanisms. First, the endothelial cells in the VEM(+) group may have been better preserved during surgery due to viscoelastic protection, resulting in slightly prolonged hydration of the corneal stroma and delayed resolution of the seroma. Second, although the clinical corneal edema was not overt, the minimal inflammatory response may have led to an increase in CCT in the millimeter range. Third, the transiently higher IOP on the 1st post-operative day in the VEM(+) group may have temporarily impaired endothelial pump function, thereby delaying the normalization of stromal fluid content and CCT. Studies such as Bamdad et al. (24) and Tang et al. (25) have documented similar patterns showing an early post-operative CCT increase that gradually regresses to baseline, especially when endothelial stress is present (26). Finally, the small sample size of our study could result in a few outlier values disproportionately affecting the mean, emphasizing the need for larger cohorts to validate these observations.

Although ACD can also be assessed with conventional A-mode ultrasound, the contact of this method with the corneal surface carries risks such as corneal abrasion and infection (27). CCT can also be measured with ultrasound pachymetry. Several studies comparing Pentacam and ultrasound pachymetry have shown that although the measurements are comparable, Pentacam tends to yield slightly thinner CCT thickness values (28). In view of these findings and to minimise the risks associated with contact-based methods, we used CCT measurements with Pentacam in our study. It is important to note that CCT is influenced by the degree of hydration of the cornea, which in turn depends on the proper function of the endothelial pump and barrier mechanisms.

The limitations of our study include its relatively short follow-up period, the small sample size, and the absence of post-operative endothelial cell count (ECC) measurements, as no specular microscopy was performed. This limitation restricts our ability to comprehensively evaluate corneal endothelial cell function and the long-term safety of the hydroimplantation technique for the corneal endothelium. Furthermore, the post-operative inflammatory response was neither assessed nor compared between groups, which may have contributed to IOP fluctuations. Patient adherence to post-operative medication was also not objectively verified. In addition, it is possible that certain patients predisposed to post-operative IOP spikes, such as steroid responders or patients with undiagnosed normotensive glaucoma, were inadvertently included in the study, which may have influenced the observed results. These factors represent additional limitations that should be taken into consideration in larger prospective studies in the future.

Conclusion

To summarize, hydroimplantation appears to be a safe and effective alternative to viscoelastic-supported IOL implantation in routine phacoemulsification surgery, particularly in appropriately selected patient groups. When performed by experienced surgeons, this technique may help minimise early post-operative IOP peaks while maintaining surgical safety. Moreover, hydroimplantation offers potential advantages in terms of surgical efficiency and cost-effectiveness. Nevertheless, larger prospective studies with extended follow-up and ECC evaluations are needed to confirm these findings and to further elucidate the long-term effects of hydroimplantation on corneal health and visual outcomes.

Ethics Committee Approval

This study was approved by the Akdeniz University Ethics Committee (Date: 08.02.2017Number: KAEK 20 No:77).

Informed Consent

Written informed consent was obtained from all patients.

Conflict of Interest

None declared.

Funding

The author declared that this study has received no financial support.

Use of AI for Writing Assistance

None declared.

Author contributions

Concept – Y.A., H.D.I., M.U., C.E.P.; Design – Y.A., H.D.I., M.U., C.E.P.; Supervision – Y.A., H.D.I., M.U., C.E.P.; Resource – Y.A., H.D.I., M.U., C.E.P.; Materials – Y.A., H.D.I., M.U., C.E.P.; Data Collection and/or Processing – Y.A., H.D.I., M.U., C.E.P.; Analysis and/or Interpretation – Y.A., H.D.I., M.U., C.E.P.; Literature Search – Y.A., C.E.P.; Writing – Y.A., C.E.P., H.D.I.; Critical Reviews – Y.A., H.D.I., M.U., C.E.P.

Peer-review

Externally peer-reviewed.