Influence of total intraocular lens diameter on efficacy and safety for in the bag cataract surgery.

CONTEXT: Intraocular lenses with variable total diameter are supposed to fit better in the capsular bag and lead to fewer complications. AIMS: This study aims to investigate the efficacy and the safety of an intraocular lens model with variable total diameter. SETTINGS AND
DESIGN: Prospective randomized intraindividual study. SUBJECTS AND METHODS: Thirty-two eyes of sixteen patients with bilateral age-related cataract received standard cataract surgery with implantation of an intraocular lens with a standard diameter in one eye (Quatrix®, Group A) and with a variable total diameter in the fellow eye (Quatrix Evolutive®, Group B). Primary study endpoints included evaluation of refraction stability and posterior capsule opacification (PCO) over a follow-up period of 6 months. STATISTICAL ANALYSIS USED: SPSS (Version 19.0) was used for statistical analysis.
RESULTS: Uncorrected and corrected distant visual acuity after 6 months were 0.24 and 0.1 LogMAR in Group A and 0.23 and 0.09 LogMAR in Group B, respectively. The objective and manifest spherical equivalent (OSE, MSE) 6 months postoperatively were + 0.65 D and + 0.62 D in Group A compared to + 0.33 D and + 0.33 D in Group B respectively (P = 0.665 for OSE, P = 0.208 for MSE). PCO-index increased statistically significant in both groups (P = 0.004 in Group A, P = 0.046 in Group B), but the difference of PCO-index between both groups was not statistically significant (P = 0.569).
CONCLUSIONS: An intraocular lens with a variable total diameter shows good visual outcomes and safety performance as well as same outcomes concerning postoperative refractive stability and development of PCO compared to an intraocular lens with standard total diameter.

RCT Entities:   Population Interventions Outcomes

Introduction

Nowadays, a variety of intraocular lenses (IOLs) with different material and haptic designs exist and most of them have a fixed total diameter. However, the dimensions of the capsular bag vary according to the axial length of the eye.[12] High myopic eyes have a bigger capsular bag diameter and vice versa for high hyperopic eyes. Moreover, the diameter of an empty capsular bag varies between 10 mm and 10.8 mm in emmetropic eyes.[34]

Due to this variation of the capsular bag diameter a special lens model, the Quatrix Evolutive® (Bausch and Lomb, Austria), was developed to offer a variable optic, haptic, and total diameter. The total diameter varies from 10.3 mm to 10.8 mm, the optic from 5.85 mm to 6.15 mm. The purpose of this modification was to improve the fixation of the IOL in the capsular bag and to avoid complications that could occur due to the instability of the IOL in the bag such as IOL-tilt, IOL-dislocation, capsular bag stretching, or capsular bag tears. Moreover, a better fixation provides less posterior capsule opacification (PCO).[567]

The present study compares two intraocular lenses of the same material and design manufactured by the same company with only one difference between them, their different total diameter. The primary aim of this study is to evaluate the efficacy and safety of the IOL model with the variable diameter, mainly concerning its refractive stability and formation of PCO over a period of 6 months.

Subjects and Methods

A prospective cohort trial was conducted in the Department of Ophthalmology in Ludwig-Maximilians-University in Munich. Sixteen patients (5 males and 11 females) with age-related cataract on both eyes and a visual acuity better than 0.9 LogMAR were included for cataract surgery. Exclusion criteria were pseudoexfoliation, zonular instability, status post trauma, and other conditions that could have any effect on the stability of the capsular bag. In addition, patients with glaucoma, corneal dystrophies, retinal pathologies or retinal surgery, pupil anomalies, and mature cataract were also excluded. All patients underwent uneventful cataract surgery using standard phacoemulsification with in the bag IOL implantation from the same experienced surgeon (C. L.). IOL selection and implantation were randomized. The study met the criteria according to the declaration of Helsinki and was approved by the Institutional Review Board of the Department of Ophthalmology. Informed consent was preoperatively obtained from every patient.

Both lens models have a biconvex, aspheric, monofocal design made of a one-piece hydrophilic acrylic material with a square-edge optic design over 360°consisting of four 6° angulated closed-loop haptics. All IOLs are preloaded in a standardized sterilized shooting-system, provided by the manufacture (Bausch and Lomb, Austria). The one IOL (Quatrix®) has a standard optic diameter of 6 mm and a total overall diameter of 11 mm whereas the other IOL (Quatrix Evolutive®) has a variable total diameter that increases from 10.3 mm to 10.8 mm with a decreasing IOL-power from 30 D to 10 D, based on a negative linear correlation between IOL-diameter and IOL-power.

Standard ophthalmic slit lamp examinations were performed 1 day, 1 week, 4–6 weeks, and 3 and 6 months after surgery. Preoperative, 6 weeks and 6 months after surgery, additional examinations included objective and manifest refraction with determining of uncorrected and corrected distant visual acuity (UDVA, CDVA). Anterior chamber depth (ACD) was quantified by anterior segment-OCT measurements with slit lamp adapted OCT imaging (Heidelberg Engineering, Heidelberg, Germany). Keratometry and biometry data were obtained using the IOL-Master 500 (Zeiss Meditec, Oberkochen, Germany) and were repeated in the pseudophakic eyes over the follow-up time. For the appropriate IOL-power calculation two formulas were used: the Haigis formula was selected for eyes with an axial length ≥22 mm and the Hoffer Q formula for axial length <22 mm. Target refraction for all patients was emmetropia.

The prediction error (PE) was calculated for each eye for every follow-up visit. Two values were obtained: the PE at 6 weeks and 6 months, respectively. The absolute values of these errors (absolute error [AE]) were compared to each other between the two lens models to observe if any IOL-model would show a lower AE.

Furthermore, after pupil dilation digital retro-illumination images of the posterior capsule were taken by an experienced slit lamp photographer. At least three images of each eye were taken at every follow-up visit and were objectively evaluated by the EPCO 2000 software (EPCO2000, Prof. Tetz, Berlin, Germany). A central optical zone of 5.85 mm that represents the smallest optic diameter of the IOL with the variable diameter was evaluated and the PCO-index was automatically calculated by the EPCO software. The PCO-index varied between 0 and 4, where 0 refers to no PCO, and 4 refers to a very strong PCO-formation.[89]

Other complications such as anterior capsule opacification (ACO), cystoid macular edema, severe anterior chamber inflammation, and haptic dislocation were documented during the follow-up period.

Statistical analysis

All data were imported into Spreadsheets of SPSS for Windows (SPSS 19.0, IBM, Armonk, NY, USA). The results were divided into two groups with regard to the IOL-model. Baseline data of the two IOL-groups were compared to each other using paired Student's t-test. The study parameters between the two groups were analyzed for statistically significant differences using Wilcoxon signed-rank test and refractive stability and PCO-formation were specified as the primary variables. The statistical significance was assumed at P ≤ 0.05.

Results

Baseline data showed no significant difference in any preoperative parameter between the groups. Mean values of the analyzed parameters pro group including P values and standard deviation are listed in Table 1. The mean age was 74 ± 8 years. The mean total IOL-diameter in Group A was the standard IOL-diameter (11 mm), whereas the mean total IOL-diameter in Group B was 10.47 ± 0.13 mm (range 10.3–10.8 mm). The axial length ranged in Group A from 20.96 mm to 24.62 mm and in Group B from 20.83 mm to 26.32 mm. No complications occurred during the surgical procedures, and the whole study population completed the follow-up period of 6 months.

Table 1

Preoperative comparison of the mean values of the intraocular lens groups

Mean values of postoperative UDVA, CDVA, objective and manifest spherical equivalent (OSE and MSE), PE, ACD, and PCO-index after 6 weeks and 6 months, as well as the P values between them, are demonstrated in Table 2. UDVA and CDVA improved in both groups after the surgery [Figure 1] und remained stable without any significant difference between the groups after 6 months (P = 0.786 for UDVA, P = 0.317 for CDVA). Safety index, which is the ratio of postoperative CDVA to preoperative CDVA, was 0.22 for Group A and 0.36 for Group B, whereas efficacy index that is defined as the ratio of the postoperative UDVA to the preoperative CDVA was 1.06 for Group A and 0.88 for Group B.

Table 2

Mean values of postoperative data (6 weeks and 6 months) compared to each other with regard to the intraocular lens group

Figure 1

Development of the mean uncorrected and corrected distance visual acuity over the follow up period with regard to the intraocular lens-model

The comparison of the change of OSE and MSE [Figure 2], AE and ACD [Figure 3] over the follow-up time between the two IOL-groups did not show any statistical significant difference (P = 0.665, P = 0.208, P = 0.357 and P = 0.918, respectively). However, the group with the variable diameter demonstrates a lower deviation of the postoperative ACD in eyes with higher ametropia [Figure 4]. Moreover, an excessive deepening of the ACD occurred in one myopic patient with a preoperative relative deep anterior chamber, as seen in Figures 3 and 4. Beyond that, this patient showed a prolonged inflammatoric reaction after the surgery that lead to a contraction of the anterior capsule. Despite the backward shift of the IOL-optic that occurred due to this reaction, no significant changes were observed in the visual acuity of the patient.

Figure 2

Distribution of the spherical equivalent of the manifest and objective refraction (D) at the last follow up examination (6 months) according to the intraocular lens-model

Figure 3

Distribution of the final anterior chamber depth (mm) after 6 months with regard to its preoperative value according to the intraocular lens-model. The outlier in this figure corresponds to the one patient that developed a prolonged inflammatoric reaction after surgery

Figure 4

Distribution of the final anterior chamber depth (mm) regarding the preoperative axial length (mm) according to the intraocular lens-model. The intraocular lens with the variable diameter demonstrates a lower deviation of postoperative anterior chamber depth in eyes with higher ametropia. The outlier corresponds to the patient that developed a prolonged inflammatoric reaction after surgery

PCO-formation between the two IOL-groups was not statistically significant over the follow-up period (P = 0.569), [Figure 5]. At the last follow-up examination, no progressive PCO-formation could be clinically detected in both groups. An anterior shift of a haptic without any movement or tilt of the lens optic was detected in two eyes, documented by slit-lamp imaging. Table 3 gives an overview of postoperative complications with regard to the IOL.

Figure 5

Development of the posterior capsule opacification-index according to intraocular lens-model

Table 3

Complications grouped by intraocular lens-model and follow-up time

Discussion

The capsular bag characteristics and its size have been already investigated in detail.[310] Moreover, some groups tried to measure either the diameter of the empty bag or the changes of its size after an IOL-implantation, whereas other groups developed formulas that predict the capsular bag diameter based on anatomical eye parameters such as axial length, ACD, and keratometry.[241112] The in the bag IOL-implantation showed that the IOL should have a specific size to fit in the bag to prevent and possibly eradicate any complications such as PCO, IOL-decentration, IOL-tilt, ACO, anterior capsule contraction syndrome, and refractive instability.[13] In 2009, a hydrophilic lens with a variable total diameter that is correlated with the IOL-power was manufactured. This lens model, has a variable optic, haptic and total diameter in order to fit properly in the variable capsular bag after lens removal.

The study was conducted to use these two lens models within one study subject. One eye received the IOL with the variable diameter related to IOL-power and the other eye the IOL with the standard diameter. The mean IOL-diameter of Group B was in this study 10.47 ± 0.13 mm. This is in conjunction with data from Mylonas et al.[14]

The OSE showed no difference between the two groups over the 6 months follow-up. However, the accuracy was better for the IOL with the variable diameter as the mean deviation to the target refraction (0 D) was only + 0.14 D 6 weeks and + 0.33 D 6 months postoperatively. The MSE showed similar results also in both groups, while Group B showed also a slightly better outcome in comparison to Group A. These findings agree with the lower PE that was calculated in the group with the variable diameter. With regard to the obtained data of the postoperative OSE and the PE in both groups, we could not find any other reason except of the usage of two different biometric formulas for the proper IOL-power calculation.

The stable OSE and MSE in both groups are in accordance with the stable UDVA and CDVA over the follow-up period. Our 6-month results regarding the CDVA on both groups were 0.1 LogMAR for the group with the standard diameter and 0.09 LogMAR for the group of the variable diameter confirming the results of Mylonas et al.[14] Moreover, the refraction stability for both lens models was controlled by analyzing the ACD-change in correlation to the axial length of the eye with no significant differences between the two IOL groups.

The formation of PCO increased significantly during the follow-up period in both groups. However, no difference was detected in the comparison between the two IOL-models. PCO and its formation concerning IOL-designs and material as well as its pathology have been studied over the years intensively.[715161718192021] Despite the fact that hydrophilic IOLs are responsible for more PCO than hydrophobic, we did not observe a progressive increase in PCO-formation in our study population.[2223] However, in all eyes, a PCO-index was determined by objective software analysis. Our study results regarding the PCO support the lack of significant differences between the two IOL-models and agree with previous published data.[14] However, the PCO-index of our study is lower and this difference can be explained due to shorter follow-up time of our study and due to the usage of a different software analyzing approach.

A limitation of this study is that 20 of the 32 eyes were hyperopic, while 12 of the 32 eyes were myopic. This inequality of the preoperative OSE explains the slight postoperative hyperopic shift of the mean postoperative OSE due to the fact that we did not want to have any myopic outcome on hyperopic eyes and vice versa.

Our study findings demonstrate that refractive stability and outcome are not mainly affected by the capsular bag diameter or the IOL-diameter rather than by precise calculation of the lens power. Furthermore, PCO-formation or anterior capsule contraction was not influenced by an IOL-type with different diameters regarding IOL-power. Despite the development of new IOL-models and designs, new promising technologies such as IOL-coating and the improvement of the surgical technique using femtosecond-laser technology could help to eradicate the vulnerable effect of PCO-formation.[2425]

Conclusion

An intraocular lens with variable total diameter shows equally good visual outcomes, safety performance and postoperative refractive stabilty as well as similar development of PCO compared to an intraocular lens with standard diameter.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.