Approximately 43.85% of patients with cataract in central China have more than 1.00 diopter (D) of preexisting corneal astigmatism.1 Uncorrected astigmatism may cause significantly decreased vision, and residual astigmatism could significantly affect the quality of life.2 Intraoperative approaches for treating astigmatism include opposite clear corneal incisions, limbal or corneal relaxing incisions, and toric intraocular lens (IOL) implantation.3 Numerous studies have shown that toric IOLs provide better uncorrected distance visual acuity (UDVA), greater spectacle independence, and lower amounts of residual astigmatism than non-toric IOLs, even when relaxing incisions were used.4 Accurate alignment of the toric IOL is a critical step in the correction of preexisting corneal astigmatism. One degree of misalignment reduces the astigmatic correction by approximately 3.3%, with more than 30° of misalignment effectively increasing the amount of preoperative astigmatism.5
Errors in the alignment of the toric IOL may be due to misalignment of the toric IOL or postoperative IOL rotation.6 Misalignment could be created by both imprecise prediction of the desired axis of the IOL alignment preoperatively and imprecise alignment intraoperatively. Manual corneal marking is usually used for the alignment of the toric IOL. The axial error of the toric IOL is usually approximately 5° when using corneal marking.7 The error in alignment can happen at several steps during the cataract surgery procedure. Intraoperatively, cyclotorsion of the eye can cause misalignment.8 Moreover, once the patient is draped, identification of the horizontal or vertical meridian may be difficult.9 Furthermore, corneal marking points are not on the same plane as the IOL. Visual errors may also occur during surgery, which may lead to axial misalignment of the toric IOL. With the recently introduced LENSAR femtosecond laser platform (LENSAR LLC), one can mark the capsular plane for alignment of the toric IOLs instead of preoperative manual corneal marking.10 In addition, capsular marking can remain visible postoperatively to help identify any rotation and guide realignment of the toric IOL to its optimal position.
The purpose of this study was to compare the accuracy of the new femtosecond laser capsular marking technique with a conventional manual corneal marking technique for toric IOL alignment.
Patients and Methods
This prospective comparative study was approved by the ethics committee of the Aier Eye Hospital and performed in accordance with the tenets of the Declaration of Helsinki and good clinical practice. All patients gave informed consent to participate in the study. The inclusion criteria included planned cataract surgery with toric IOL implantation, age between 40 and 85 years old, and preoperative regular corneal astigmatism greater than 1.00 D.11 Patients with any history of previous intraocular surgery, abnormal iris or pupil deformation, macular degeneration or retinopathy, severe dry eyes, or irregular astigmatism were excluded from the study.
Seventy-two consecutive patients (72 eyes) were divided into two groups based on the method of toric IOL alignment. One group (n = 36) underwent femtosecond laser capsular marking of the reference and target axes (femtosecond laser capsular marking group) and the other (n = 36) underwent manual corneal marking (manual marking group).
Before enrolling in this study, patients underwent an ophthalmic examination including slit-lamp bio-microscopy, retinal evaluation, and routine biometry. For all patients, the OPD Scan-III (Nidek) system was used for surgical planning and IOL axis placement. IOL cylinder power and axis placement were calculated using the online calculator for each IOL ( http://www.acrysoftoriccalculator.com). Surgically induced astigmatism of 0.25 D was assumed in all cases. Maximum possible correction of the astigmatism was attempted, taking into consideration the surgically induced astigmatism.
All patients in the femtosecond laser capsular marking group were evaluated preoperatively (seated upright position) using the OPD Scan-III for iris registration. The OPD Scan-III allows surgeons to obtain an infrared image of the eye in the dilated or undilated state that illuminates the blood vessels on the sclera, iris crypts, and iris nevi for landmarking. The high-resolution mesopic images from the OPD Scan-III for iris registration were coupled with the image acquired from the LENSAR femtosecond laser platform12 (Figure 1). The latest software operating system of LENSAR (Streamline IV) allows for the creation of markers (used for axis determination) on the capsulotomy edge. Figure 2 shows the steps of the marking method. The markers were two small tabs at the capsulotomy edge with a height of 300 µm and an arc length of 10° at their base (Figure 2A). After the implantation of the toric IOL during cataract surgery, the axis markers on the IOL were aligned with the capsulotomy markers.
An image from the femtosecond laser system showing the iris-registration image according OPD Scan-III (Nidek).
(A) The marks are two small tabs at the capsulotomy edge with a height of 300 µm and an arc length of 10° at their base. (B) With the guidance of the previously marked reference marking, axis marking is performed using a Mendez ring. (C) The corneal marker was made by a 25-gauge needle with a tip stained with a sterile blue ink. (E) For the femtosecond laser capsular marking group, the IOL was aligned to the target axis according to the two small tabs at the capsulotomy edge. (F) For the manual marking group, the IOL was aligned to the target axis according to the corneal marker.
The manual marking group included 36 eyes that were manually marked in a two-step procedure. The first step was the reference marking, using a water-level bubble marker (Nuijts-Lane marker; ASICO LLC). In the operating room just before surgery, the patient was instructed to focus on a distant target while in a sitting position to compensate for possible cyclotorsion that may occur when lying supine. Using a toric reference marker, the horizontal points of the 0° and 180° axis were marked with the eyes open. The next step was an axis marking procedure after femtosecond laser procedures. With the guidance of the previously marked reference marking, axis marking was performed using a Mendez ring (Figure 2B). A 25-gauge bent needle with the tip stained with a sterile blue ink marker was used to make an anterior stromal puncture as described by Bhandari and Nath13 (Figure 2C). Matching the target axis of the marks in the cornea was attempted in all patients once.
All cases underwent femtosecond laser–assisted cataract surgery (LENSAR LLC) with implantation of the AcrySof toric IOL or AcrySof RESTOR toric IOL (Alcon Laboratories, Inc) performed by a single surgeon (YW). The laser procedure was initiated by docking the laser using a non-contact, fluid-filled patient interface, enabling imaging of the anterior chamber. LENSAR uses augmented reality, a proprietary method of acquiring biometric data using ray-tracing to create a three-dimensional reconstruction. The images and treatment plan were confirmed before the laser treatment was started. A 5.2-mm capsulotomy was performed, followed by lens fragmentation. The laser was disconnected and the remainder of the surgery was performed as phacoemulsification. A 2.2-mm clear corneal incision was made at 120° with a keratome. Coaxial phacoemulsification (Centurion Vision System; Alcon Laboratories, Inc) was performed, and an AcrySof toric IOL or AcrySof RESTOR toric IOL was implanted in the capsular bag. For the femtosecond laser capsular marking group, the IOL was aligned to the target axis according to the two small tabs at the capsulotomy edge (Figure 2D). For the manual marking group, the IOL was aligned to the target axis according to the corneal marker (Figure 2E). After matching the axis to the marking, the surgeon made the markings again using a sterile 25-gauge bent needle for postoperative follow-up observation.
Postoperative examinations were performed within 1 hour of the operation and at 1 day, 1 week, 1 month, and 3 months postoperatively. All patients were photographed using slit-lamp microscopy through dilated pupils (minimum 6 mm) at each follow-up visit.14 The patient's head was properly positioned behind the slit lamp without any tilting. The presence of markings and the error in the alignment of the toric IOL were recorded. At the 1- and 3-month follow-up visits, UDVA and corrected distance visual acuity were assessed using a backlit Early Treatment Diabetic Retinopathy Study chart presented at 4 m (Precision Vision).
Error in the Alignment of the Toric IOL
The error in the alignment of the toric IOL was defined as the misalignment of the toric IOL and postoperative IOL rotation.15 Misalignment was defined as the difference between the desired toric IOL axis and the actual toric IOL axis within 1 hour after the surgery. To evaluate the misalignment, the slit-lamp photograph was taken within 1 hour after surgery in the sitting position. Rotation of the toric IOL was defined as the difference between the implanted toric IOL axis and toric IOL axis at consecutive follow-up visits. For the femtosecond laser capsular marking group, the capsular markings served as the reference spots to determine the alignment error of the toric IOL (Figure 3A). For the manual marking group, markings in the corneal stroma served as the reference spots to determine the alignment error of the toric IOL (Figure 3B). To avoid the disappearance of marking points in the corneal stroma, if the corneal stroma puncture mark had not disappeared, markings were made at the marking points again and stained with ink at each follow-up visit. If the marking points had totally disappeared, the alignment error could not be evaluated.
(A) For the femtosecond laser capsular marking group, the capsular markers (tabs at the capsulotomy edge) served as the reference spots to determine the rotation of the toric intraocular lens (IOL). (B) For the manual marking group, marker points stained with ink in corneal stroma (blue line on the peripheral cornea) served as the reference spots to determine the rotation of the toric IOL.
We performed a post hoc statistical power analysis in this study, based on a consecutive effect size between the two groups (mean difference = 2.5, standard deviation = 3.0). Our sample size (36 eyes each group) had a greater than 95% power at the 5% significance level.
All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS version 15.0; SPSS, Inc). Descriptive results are presented as the mean and standard deviation for normally distributed continuous variables, or median and interquartile range for non-normally distributed continuous variables. The t test and Mann-Whitney U test were used to analyze the difference between the two groups for normally distributed and non-normally distributed continuous variables, respectively. For categorical variables, the chi-square test or Fisher's exact test were used to detect the differences between the two groups. A two-sided P value less than .05 was considered statistically significant.
Between July and November 2018, a total of 72 consecutive eyes (from 72 patients) from Aier Eye Hospital of Wuhan University Hospital were enrolled in this study. In the femtosecond laser capsular marking group, the newest femtosecond laser platform was used to make capsular markings in 36 eyes. In the manual marking group, manual corneal markings were made in the other 36 eyes. There were no intraoperative or postoperative complications in either group. The mean preoperative corneal astigmatism was 1.83 ± 0.75 D (range: 0.75 to 3.25 D) in the femtoscond laser capsular marking group and 1.92 ± 0.68 D (range: 0.81 to 3.73 D) in the manual marking group; there was no significant difference between the two groups (P = .60). Table 1 shows the demographic and other ocular biometric parameters between the two groups.
Demographic and Ocular Biometric Parameters Before Surgery
The presence of markers at each postoperative follow-up visit are summarized in Table A (available in the online version of this article). In the femtosecond laser capsular marking group, the capsular markings were retained for at least 3 months. However, in the manual marking group, 22.2% of the corneal markers disappeared within 1 month and all markings had disappeared within 3 months. The proportion of eyes with retained markings was significantly lower in the manual marking group after 1 and 3 months of follow-up (P = .005 at 1 month of follow-up and P < .001 at 3 months of follow-up).
No. of Eyes With Visible Markers at Each Follow-up Visit
Table 2 shows the observed misalignment of the toric IOL, the alignment error of the toric IOL, UDVA, and residual astigmatism between the two groups at the 1-month follow-up visit. The residual refractive cylinder at 1 month postoperatively was 0.41 ± 0.26 D (range: 0.00 to 0.55 D) in the femtosecond laser capsular marking group and 0.45 ± 0.31 D (range: 0.00 to 1.00 D) in the manual marking group (P = .56). The mean mis-alignment of the toric IOL was 1.5° ± 1.4° in the femtosecond laser capsular marking group and 4.4° ± 2.1° in the manual marking group at 1 hour postoperatively (P < .01). The mean alignment error of the toric IOL was 1.6° ± 1.3° in the femtosecond laser capsular marking group and 4.8° ± 2.5° in the manual marking group at 1 month postoperatively (P < .001).
Misalignment of Toric IOL, Alignment Error of Toric IOL, UDVA, and Residual Astigmatism at 1 Month Postoperatively
This study included 3 months of follow-up. Most cor-neal markers remained in both groups at the 1-month follow-up, but all markers had disappeared at 3 months after surgery. Therefore, this study compared the results between the two groups at 1 month after surgery.
With the manual corneal marking method using a bubble marker, a mean alignment error of 4.8° ± 2.5° was observed at the 1-month follow-up. The manual marking methods have inherent sources of errors, such as smudging or fading of the dye, broad marking leading to variation of a few degrees, and Bell's phenomenon. Instrument-specific problems, such as the toric axis marker having a minimum scale of 5° to 10°, make precise axis marking impossible.16 Moreover, manual marking is associated with a significant learning curve and intersurgeon variability may be observed in the accuracy of marking. To reduce the error of manual corneal marking, the iris registration technique was introduced by Osher.17 It uses the landmarks of the iris, including iris crypts, nevi, and Brushfield spots, to place the axis markers. This method eliminates the time-consuming process of marking patients on the surgical day and allows placement based on anatomical landmarks. The Osher Toric Alignment System constituted the basis for the creation of a noticeable number of image-guided systems. However, traditional manual corneal marking or image-guided corneal marking are at the level of the cornea, which is not on the same plane as the toric IOL. Visual errors may exist during surgery, which may lead to alignment errors of the toric IOL. In this study, we used the OPD Scan-III for iris registration and the LENSAR femtosecond laser platform for capsular marking to guide the toric IOL. We found statistically significant differences between the manual marking and femtosecond laser capsular marking methods, with less error in the alignment of toric IOL in the femtosecond laser capsular marking group than in the manual marking group (1.6° ± 1.3° versus 4.8° ± 2.5°). These results confirm the benefit of the laser-assisted capsular marking system for toric IOL alignment. Marking at the level of the capsulotomy offers an axis reference at the same plane as the toric IOL, avoiding parallax issues that axis markings at the level of the cornea may have.10
Another challenging step for the toric IOL is postoperative assessment of IOL rotation. Most toric IOL corneal marking techniques include making gentle scratches and then staining the scratches with dye. The corneal markings always disappear from 1 day to 1 week after surgery. The absence of preoperative corneal markings significantly affects the judgment of toric IOL axis rotation. To make the corneal markings visible for longer periods of time, we used a modified technique known as anterior stromal puncture for staining, as detailed in the study by Bhandari and Nath.13 Our study showed that most corneal markings made using anterior stromal puncture can be retained for more than 1 month (77.78%), but all disappeared within 3 months (0%). However, the lens capsular markings were retained for 3 months (100%). Long-term retention of capsular markings helps assess the postoperative rotation of the toric IOL. The capsulotomy tabs remain present after surgery as an anatomical landmark to facilitate the assessment of IOL axis position during the early postoperative follow-up period. Aside from the clinical postoperative assessment, the capsule markings may be used in cases in which IOL rotation evaluation is required postoperatively. The results showed that the rotation angle of the femtosecond laser capsular marking group was smaller than that of the manual marking group. The difference in rotation data between the two groups may not be the difference in IOL rotation angle data between the two groups but may be due to measurement differences. Because of the distance between the corneal markings and the markings of the toric IOL and the diffusion of the dye color, there may be a judgment error when measuring the rotation angle of the IOL. However, the capsular marking point is close to the IOL marking point, so the rotation angle of the IOL can be judged more accurately.
The iris registration method is used to improve the matching accuracy of femtosecond laser–assisted capsular marking. A previous study showed that the eyeball usually rotates approximately 2° from the sitting position to the supine position.18 However, with femto-second laser–assisted capsular labeling, due to the operation of attraction, the angle of eyeball rotation is larger, ranging from 0° to 17°, with an average of 5.8°.12 The LENSAR femtosecond laser platform sets the matching range for eyeball rotation. When the eyeball selection is more than 21°, a matching error will be highlighted and the platform needs to be docked again. However, no such wide range selection is found in this study.
As mentioned above, compared with the traditional manual marking method or the CALLISTO Eye and VERION Image Guided Systems, the femtosecond laser capsular marking method simplifies the operation steps and omits the preoperative manual marking steps. Moreover, the capsular marking and IOL are in the same plane, which avoids the observation error of the manual mark. Third, the capsular marking is permanent, which is helpful to observe the axial position of the IOL. In the future, we will compare the accuracy of capsule and image labeling.
However, making notches or marks on the capsule carries with it the risk of also creating tags or weak spots in the capsule that could lead to anterior capsule discontinuities and possible extended tears in the anterior capsule. Previous studies in pig eyes showed that femtosecond laser capsulotomies with capsular markers were equivalent in tensile strength and extensibility to standard femtosecond laser capsulotomies.19 However, this may not translate directly to humans. In this study, no complications, such as rupture of the capsule, were found. In the future, we will further observe the tensile properties following capsular marking. In addition, the follow-up period of this study was 3 months and there was no change in the location of the capsular markings associated with capsular shrinkage. In the long term, whether the location of the capsular markings changes with capsule mechanization or shrinkage remains to be further observed. IOL misalignment was significantly lower in the femtosecond laser capsular marking group than in the manual corneal marking group. In addition, the long-term preservation of the capsular markings is helpful in evaluating the rotation of the toric IOL. This new axis marking modality seems to overcome several disadvantages of the existing axis marking techniques and offers surgeons the versatility of avoiding parallax-related errors.
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- Maedel S, Hirnschall N, Chen YA, Findl O. Rotational performance and corneal astigmatism correction during cataract surgery: aspheric toric intraocular lens versus aspheric nontoric intraocular lens with opposite clear corneal incision. J Cataract Refract Surg. 2014;40(8):1355–1362. doi:10.1016/j.jcrs.2013.11.039 [CrossRef]
- Kessel L, Andresen J, Tendal B, Erngaard D, Flesner P, Hjortdal J. Toric intraocular lenses in the correction of astigmatism during cataract surgery: a systematic review and meta-analysis. Ophthalmology. 2016;123(2):275–286. doi:10.1016/j.ophtha.2015.10.002 [CrossRef]
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- Oshika T, Inamura M, Inoue Y, et al. Incidence and outcomes of repositioning surgery to correct misalignment of toric intraocular lenses. Ophthalmology. 2018;125(1):31–35. doi:10.1016/j.ophtha.2017.07.004 [CrossRef]
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- Webers VSC, Bauer NJC, Visser N, Berendschot TTJM, van den Biggelaar FJHM, Nuijts RMMA. Image-guided system versus manual marking for toric intraocular lens alignment in cataract surgery. J Cataract Refract Surg. 2017;43(6):781–788. doi:10.1016/j.jcrs.2017.03.041 [CrossRef]
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Demographic and Ocular Biometric Parameters Before Surgerya
|Variable||Femtosecond Laser Capsular Marking (n = 36)||Manual Marking (n = 36)||P|
|Age (y)||68.77 ± 8.63||68.63 ± 10.44||.62|
|Corneal cylinder (D)||1.83 ± 0.75||1.92 ± 0.68||.60|
|UDVA (logMAR)||0.66 ± 0.32||0.67 ± 0.28||.89|
|CDVA (logMAR)||0.53 ± 0.27||0.47 ± 0.31||.38|
|Kf (D)||45.17 ± 2.16||44.52 ± 2.23||.21|
|Ks (D)||47.12 ± 3.17||46.78 ± 2.83||.63|
|ACD (mm)||3.36 ± 0.08||3.34 ± 0.11||.35|
|AXL (mm)||24.61 ± 0.65||24.27 ± 0.82||.06|
|Target axis of IOL implantation||77.12 ± 66.83||74.24 ± 61.48||.85|
Misalignment of Toric IOL, Alignment Error of Toric IOL, UDVA, and Residual Astigmatism at 1 Month Postoperativelya
|Variable||Femtosecond Laser Capsular Marking (n = 36)||Manual Marking (n = 36)||P|
|Refraction sphere (D)||−0.48 ± 0.32||−0.46 ± 0.38||.81|
|Residual refractive astigmatism (D)||−0.41 ± 0.26||−0.45 ± 0.31||.56|
|UDVA (logMAR)||0.07 ± 0.06||0.07 ± 0.05||1.00|
|Misalignment of toric IOL (degrees)||1.5 ± 1.4||4.4 ± 2.1||< .01|
|Alignment error of toric IOL (degrees)||1.6 ± 1.3||4.8 ± 2.5||< .01|
No. of Eyes With Visible Markers at Each Follow-up Visita
|Visit||Femtosecond Laser Capsular Marking (n = 36)||Manual Marking (n = 36)||P|
|1 day||36 (100%)||36 (100%)||1.00|
|1 week||36 (100%)||33 (91.67%)||.24|
|1 month||36 (100%)||28 (77.78%)||.01|
|3 months||36 (100%)||0 (0%)||< .01|