Capsular bag stabilization after conventional cataract surgery has become a major requirement for various types of intraocular lenses (IOLs) currently on the market. Toric, multifocal, and mono-focal spherical aberration–correcting IOLs require exceptional good rotational and capsular bag stability after cataract surgery. Different characteristics such as overall diameter or textured haptic surface seem to be effective with regard to rotational stability.1 In toric IOLs, depending on the power of the torus, the corrective ability decreases with the amount of misalignment. Considering an initial implantation axis offset, 5 degrees may be seen as the critical limit of acceptable misalignment for a toric IOL.2 To obtain an immediate satisfying refractive outcome, both centration and early axial stability of an IOL are crucial. Anterior and posterior IOL movement within the first months after IOL implantation has been observed for three-piece and one-piece IOLs.3,4
The purpose of the current study was to investigate rotational and axial stability, decentration, and tilt of a new aspheric hydrophobic IOL featuring C-loop haptics with so-called cornerstone technology for enhanced capsular bag stability.
Patients and Methods
This prospective interventional case series was conducted at the Department of Ophthalmology at the Medical University of Vienna. A total of 130 eyes of 68 patients prior to cataract surgery were included in this study. Surgeries were conducted between January and October 2019. Written informed consent was obtained from all patients before inclusion. All study procedures followed the tenets of the Declaration of Helsinki. The study was approved by the local ethics committee of the Medical University of Vienna (1978/2018) and registered to a public clinical trials registry (NCT03803852).
Inclusion criteria were unilateral or bilateral age-related cataract, age between 45 and 95 years, and preoperative pupil width of more than 7 mm under full pharmacological dilation. Exclusion criteria were pseudoexfoliation syndrome, previous ocular trauma, uncontrolled glaucoma, uncontrolled ocular disease, a blind fellow eye, corneal scarring, proliferative diabetic retinopathy, intraoperative complications such as anterior and posterior capsule tear or zonular weakness, pregnancy, and lactation.
A preoperative visit was conducted 1 to 2 weeks prior to surgery. This visit included standard biometry such as axial length (AXL) and anterior chamber depth (ACD) by an IOLMaster 700 (Carl Zeiss Meditec AG), visual acuity measurement, and anterior segment examination with a swept-source optical coherence tomographer (SS-OCT) (Casia2; Tomey Corporation) including assessment of the anterior chamber or aqueous depth (AQD), lens thickness, and crystalline lens equatorial diameter (CED). Standard anterior segment and fundus examinations were conducted at the slit lamp.
The preloaded monofocal single-piece Rayner RAO800C hydrophobic IOL (Rayner Intraocular Lenses Ltd) has an overall diameter of 12.5 mm, an optic diameter of 6 mm, and non-angulated C-loop haptics with anti-vaulting technology. The 360-degree sharp-edged optic has an aberration-free posterior aspheric surface. Cornerstones attached to the optic besides the haptic insertion guarantee optimal capsule bag stability. The nozzle of the RayOne injector has a diameter of 1.65 mm and is angulated by 45 degrees.
All patients received standard manual phacoemulsification surgery conducted by one experienced surgeon (RM). Patients were implanted in either one or both eyes with a Rayner RAO800C hydrophobic acrylic IOL. To avoid an implantation axis bias, a randomization list using RandList V1.2 (DataInf GmbH) was created prior to the study. IOLs were randomly assigned to four different implantation axes (0 ± 10, 45 ± 10, 90 ± 10, and 135 ± 10 degrees). All surgeries were performed under topical anesthesia. Oxybuprocaine (institutional composition) eye drops were instilled 5 to 10 minutes and immediately before surgery. To achieve maximum preoperative pupil dilation, phenylephrine hydrochloride 10% (Ursapharm) and tropicamide 0.5% (Agepha Pharma) eye drops were instilled three times within 30 minutes prior to surgery.
A 2.2-mm temporal posterior-limbal self-sealing incision and two paracenteses offset by 45 degrees were created. The anterior chamber was filled with a dispersive ophthalmic viscoelastic device (Eyefill HD; Bausch & Lomb). A continuous curvilinear capsulorhexis sized 5 to 5.5 mm to guarantee optic overlap was created with a self-bent 27-gauge needle. Hydrodissection was followed by phacoemulsification. After coaxial irrigation/aspiration, the capsular bag was expanded with a cohesive ophthalmic viscoelastic device (Provisc; Alcon Laboratories, Inc). A preoperatively prepared sealed envelope containing a sheet with the predetermined implantation axis was opened and shown to the surgeon. The assigned IOL was implanted and rotated to the preoperatively assigned axis. After the IOL had completely unfolded, the remaining ophthalmic viscoelastic device was aspirated by applying high flow and high vacuum settings with special attention to the bag equator and retrolental space behind the IOL. No capsular tension rings were used throughout the study. At the end of surgery, the intraocular pressure was kept on a lower normotensive level. After hydration of the surgical incision, a video clip capturing the actual IOL axis was made. The conjunctiva was gently moved with a swab to differentiate between movable conjunctival and non-movable episcleral vessels and Axenfeld loops.
Rotational Stability Evaluation
For axis assessment during the follow-up visits, a method described in detail before was applied.1 In short, the IOL axis, meaning the actual axis position at the end of surgery with the patients still supine on the operating table, was compared with a static line between two non-movable anatomic characteristics (eg, two Axenfeld loops or bifurcations of episcleral vessels) (Figure 1). A snapshot of the video clip made at the end of surgery served as baseline measurement. Changes of the angle between the IOL axis and the reference axis at the follow-up visits were recorded as rotation in degrees. Follow-up visits were scheduled after 1 hour, 1 week, 1 month, and 4 to 7 months (4 months). For comparability, at each follow-up visit, retroillumination pictures to record the position of the IOL were made.
Snapshot of the video made at the end of surgery. (A) A reference axis A is drafted between two unmovable episcleral vessels. (B) A second axis is drafted between the two axillar optic-haptic junctions. Axis A' is a translation of the reference axis A and shifted until it crosses the IOL axis B. Angle alpha identifies the baseline angle for rotational stability assessment.
Decentration, tilt, and pseudophakic AQD were assessed using the anterior segment SS-OCT.
At the 1-week and 4-month follow-up visit, an anterior segment SS-OCT was recorded to determine IOL decentration, tilt, and pseudophakic AQD. Corrected distance visual acuity (CDVA) was assessed at 1 week, 1 month, and 4 months using a Snellen chart. Results were converted to logMAR units. If patients suffered from preexisting vision-limiting pathologies such as dry macular degeneration or amblyopia, they were excluded from visual acuity analysis.
The primary outcome measure was the absolute rotation of the IOL from end of surgery to 4 months. According to the American National Standards Institute (ANSI), at least 100 IOL evaluations are necessary for rotational stability assessment. To compensate for an approximate dropout rate of 20% experienced in earlier studies, 120 eyes were included initially. Due to actual dropouts in the early phase of the study, 10 additional eyes were included to meet the ANSI guidelines.
Descriptive statistics presented as mean ± standard deviation or as median (range). The one-way analysis of variance test was used to test differences in rotation regarding the different implantation axes of 0, 45, 90, and 135 degrees.
Secondary outcomes included postoperative IOL decentration and tilt and the correlation between AXL, CED, and absolute rotation.
Correlations between absolute rotation, CED, and AXL were calculated using Spearman`s correlation coefficient. A P value of less than .05 was considered statistically significant throughout.
An increasing demand on premium IOLs has led to an evolvement in IOL design in recent years. Different haptic overall diameters and haptic designs have been used to ensure axial stability and rotational stability and to decrease the risk of decentration and tilt. These features are of particular importance in toric, multifocal, and monofocal spherical aberration–correcting IOLs.
The discrepancy regarding at which level preoperative corneal astigmatism should be treated was the topic of a recent literature review. The authors concluded that a residual postoperative astigmatism of 0.50 D or less should be aimed at to obtain an optimum visual function.5 When considering this recommendation, more than two-thirds of patients with cataract could benefit from a toric IOL.6 Additionally, uncorrected distance visual acuity in multifocal IOLs is negatively affected by postoperative residual astigmatism of more than 0.50 D.7 Therefore, an increasing demand on toric monofocal and multifocal IOLs is expected.
The current study focused on postoperative IOL rotation of a new hydrophobic acrylic IOL featuring C-loop haptics with so-called cornerstones to ensure optimal stabilization in the capsular bag.
The time-point at which the axis position of the IOL should be assessed first differs in most of the pertinent studies. Many studies report that baseline measurement was conducted “immediately” after surgery,8,9 but no details are given regarding the exact time of the first measurement. Previous studies have shown that the time window in which most of the rotation occurs is within the first postoperative hour.1,2,10 In the current study, rotational stability of the Rayner RAO800C IOL was assessed from end of surgery with the patient still supine on the operating table. The method described allows precise measurement of the IOL axis, excluding measurement noise resulting from head tilt, cyclotorsion, or primary implantation axis offset when using the intended axis as a reference as reported before.2
The RAO800C IOL showed the highest rotation within the first hour after the surgery. Although median rotation of 1.6 degrees was low, a maximum rotation of 86.2 degrees was observed. Rotation decreased to a minimum of 0.6 degrees of median rotation between 1 week and 1 month, with one IOL rotating more than 5 degrees. Nevertheless, severe rotation within the first week was observed. In total, 23.8% of the IOLs rotated more than 5 degrees and 11% rotated more than 10 degrees from their initial axis at the end of surgery to 4 months.
Tognetto et al11 conducted a study in the laboratory environment and showed that the highest decrease in optical quality of a toric IOL correcting a corneal astigmatism of 3.00 D occurs between 10 and 20 degrees of rotation. The authors concluded that rotation of more than 10 degrees should prompt a repositioning intervention. According to the current study results, a considerable number of IOLs might have needed repositioning surgery to obtain optimum results for astigmatism correction if toric IOLs had been used.
Factors adversely influencing rotational stability such as AXL have been observed previously.8,12,13 In our study, no significant correlation between AXL and overall rotation from end of surgery to 4 months was found (r = −0.048). Lee and Chang13 hypothesized that a longer AXL and consequently an IOL of lower power are correlated with capsular bag size.
We measured the CED preoperatively with an anterior segment SS-OCT (Casia2). The SS-OCT detects the anterior and posterior radii of the lens capsule curvature and consequently predicts the equatorial diameter beyond the iris. All measurements were done under full pharmacological pupil dilation to guarantee maximum recognition of the crystalline lens. Interestingly, the absolute overall IOL rotation was not correlated to the preoperative measured CED. This finding suggests that a larger capsule bag is no risk factor for postoperative IOL rotation.
IOLs with an overall IOL diameter of less than 13 mm seem to provide less rotational stability. Although the largest lens equatorial diameter observed in our study was 11.3 mm, the overall IOL diameter of 12.5 mm might not have generated enough force with respect to the capsule bag equator to stabilize the IOL in the early postoperative phase. A recent study investigating the Envista toric IOL (Bausch & Lomb) with an overall diameter of 12.5 mm showed a mean rotation of 3.85 ± 10.98 degrees.14 The Rayner IOL in our study with the same overall diameter showed similar results of 5.53 ± 10.46 degrees of mean rotation. Further, a study comparing three similar IOLs with C-loop haptics, two with a total diameter of 13 mm (Acrysof, Tecnis) and the Envista with a total diameter of 12.5 mm, applying the same method as in the current study, favored the 13-mm IOLs.10
However, in addition to the overall diameter, characteristics of the haptic material, resilience, and surface structure may play an important role. The Rayner RAO800C IOL has a capsular bag contact of 119 degrees and haptic compression force of 0.39 mN (39.8 mg, personal communication with the manufacturer, July 8, 2020) in an average 10-mm capsular bag. The Envista IOL in the previous study has a similar capsular bag contact of 110 degrees and an even increased compression force of 1.24 mN (126 mg) based on a 10-mm capsular bag.15 However, the broad contact angle and the high haptic compression force did not compensate for the obviously small overall diameter. Adhesive or textured haptics appear to be key factors for rotational stability during the early postoperative period.1
One published study reported rotational stability of the hydrophilic Rayner 600S IOL, a modified version of the 600C IOL with axis marks. In this study, excellent results with no IOL rotating more than 5 degrees from immediately, meaning 1 hour, after surgery to 3 to 6 months of follow-up in 66 eyes were reported.16 The 600C IOL features a similar 12.5-mm overall diameter and a broad haptic base as the 800C IOL in our study. Missing cornerstones and the hydrophilic material are the main differences. Unfortunately, the IOL position was not assessed directly at the end of surgery. Therefore, potential early rotation occurring within the first hour after operation was inherently missed in this evaluation. Nevertheless, in our study clinically significant IOL rotation was observed even when using the IOL axis position at 1 hour instead of end of surgery as a reference. Nine (8%) of 110 evaluable IOLs rotated more than 5 degrees from 1 hour to 4 months postoperatively. Figure A (available in the online version of this article) shows one case of severe rotation after 1 hour of follow-up.
Case of severe rotation after 1 hour of follow-up. Baseline angle at the end of surgery (EOS) was 53.6 degrees. Counterclockwise rotation of 1.4 degrees from EOS to 1 hour (1h), clockwise rotation of 28 degrees from 1h to 1 week (1w), clockwise rotation of 0.3 degrees from 1w to 1 month (1m), and clockwise rotation of 1.9 degrees from 1m to 4 to 7 months (4m). An overall clockwise rotation of 28 degrees was observed from EOS to 4m.
Decentration and tilt are other key attributes of premium IOLs. The importance of proper centration and minimal tilt in aspheric IOLs has been the topic of numerous publications before.17–20 It has been shown that the optical performance of aberration-correcting aspheric IOLs is particularly susceptible to decentration and tilt. The higher its corrective power for aberrations, the higher the optical degradation in case of decentration and tilt.21 Decentration and tilt in our study were measured with an anterior segment SS-OCT. As a reference, the corneal vertex is considered. The IOL investigated in our study showed low horizontal (0.09 ± 0.14 mm) and vertical (0.09 ± 0.14 mm) decentration after 4 months. The same applies for horizontal (4.78 ± 1.36 degrees) and vertical (1.58 ± 1.10 degrees) tilt. The broad haptic may support capsule bag adaption. In a recent study, decentration and tilt of three commonly implanted IOLs (Acrysof, Tecnis, and Envista) were evaluated after 6 months.10 Decentration and tilt are comparable to the results in our study. A Purkinje meter described before was used.22 Although in these IOLs decentration was slightly more pronounced to the inferonasal side, in the current study, decentration showed a slight superotemporal tendency. Minor differences in mean amount and direction of decentration between the IOLs most likely arise from the different measurement methods. The Purkinje meter uses the pupil center of the dilated pupil as a reference, which has been shown to deviate from the undilated pupil center. An inferotemporal shift of the dilated pupil was observed.23 Although decentration and tilt in our study were also measured under full pharmacological dilation, the SS-OCT uses the corneal vertex as a reference. Differences in pupil width should not affect the results.
Postoperative axial movement affects the effective lens position of an IOL. Hyperopic and myopic shifting can result within the early postoperative period. An immediate myopic shift followed by a delayed small hyperopic shift has been observed in three-piece IOLs after 1 week. The authors concluded that a memory loss of the angulated C-loop haptics may be responsible for the myopic shift within the first week.3 In the current study, AQD was not measured within the first week and therefore forward movement of the IOL, even in a one-piece IOL, cannot be ruled out. A similar posterior shift has been reported in a one-piece IOL from 1 month to 1 year (0.033 mm).24 The resulting median absolute refractive effect was 0.05 D. We found a posterior shift of 0.052 ± 0.055 mm from 1 week to 4 months. This is half as much as previously reported by Wirtitsch et al,4 observing an IOL shift of 0.113 mm with an Acrysof SA60AT, which is similar in design to the IOL in our study (6-mm optic diameter, 13-mm overall diameter, and no haptic angulation). The broader non-angulated haptic base with cornerstones may promote earlier axial stability in our study. A similar posterior shift from 1 week to 3 months was found by a study with a mean posterior shift of 0.07 ± 0.30 mm in the one-piece Tecnis IOL using Scheimpflug technology.25 However, the high standard deviation of 0.3 mm in this study compared to 0.055 mm in our study indicates a greater variability. The posterior optic offset of the Tecnis IOL may be responsible for greater axial movement during.
Interestingly, posterior IOL shift in our study was more pronounced in short eyes. This may be explained by the narrower anatomical conditions and the thicker optics of higher power IOLs.
The Rayner RAO800C IOL showed a high propensity to rotate within the first postoperative week. The IOL remained stable after 1 week. Comparatively high proportions of IOLs rotating more than 5, 10, and 20 degrees were observed. Low values of decentration and tilt make this a promising platform for multifocal or spherical aberration–correcting optics. Between 1 week and 4 months, axial IOL optic shift was minimal and posteriorly directed and more pronounced in short eyes. Mean CDVA was −0.043 ± 0.073 logMAR after 1 week.