Stability of neodymium:YAG laser posterior capsulotomy in eyes with capsular tension rings

Yang Kyung Cho, Min Sun Kim

Department of Ophthalmology, St.Vincent’s Hospital, College of Medicine, The Catholic University of Korea, Seoul 06591,Republic of Korea

Abstract● AIM: To evaluate the stability of neodymium (Nd):YAG laser posterior capsulotomy in eyes with capsular tension rings (CTRs).

● KEYWORDS: Nd:YAG laser; capsulotomy; capsular tension ring

INTRODUCTION

I t is important to polish the posterior capsule during cataract surgery to remove the remaining cortical fiber that can hinder visual recovery after cataract surgery[1].

In the presence of zonular weakness, it is not easy to polish the posterior capsule because zonular weakness causes frequent anteroposterior movement of the posterior capsule[2].The resultant remaining posterior capsular fiber or proliferation of equatorial lens epithelial cells (LEC) can cause posterior capsule opacity (PCO) after cataract surgery, which can be removed by neodymium (Nd):YAG laser posterior capsulotomy.Nd:YAG laser capsulotomy can be done easily in a short time, and immediate recovery of visual acuity is possible[3].However,there are several reports of complications following Nd:YAG laser posterior capsulotomy, such as intraocular lens (IOL)dislocation, IOL damage, as well as retinal complications[4-7].

The stability of the IOL after Nd:YAG laser capsulotomy can be affected by the type of ⅠOL and the fibrotic reaction between the IOL and posterior capsule[6-8].

We assume that intraocular devices, such as IOLs and capsular tension rings (CTRs), inserted inside the capsular bag can affect the tension of the capsular bag due to the intrinsic forces of the device itself.With these intrinsic forces inside the capsule, when an Nd:YAG laser is applied to the posterior capsule to make an opening, the forces of the device, which affect capsular tension, can deform the shape or size of the opening.This deformity of the capsular opening can differ according to the intrinsic forces inside of the capsule, such as IOL type, material, and the presence of CTRs[9].We regarded the enlargement of posterior capsulotomy area according to the time after Nd:YAG laser capsulotomy as being related to the maintenance of CTR centrifugal stretching force the same way that the anterior capsular opening contracture is regarded as the centripetal contracture force of the continuous curvilinear capsulorhexis (CCC) margin due to zonular laxity[10].

In this study, we evaluated the stability of the area of capsulotomy as well as the change in anterior chamber depth (ACD).As far as we know, this is the first study evaluating the effect of posterior capsulotomy in CTR-inserted eyes.

SUBJECTS AND METHODS

Ethical ApprovalThe Institutional Review Board (IRB)/Ethics Committee approval of St.Vincent’s hospital was obtained (approval number: VC23RISI0020).All research was conducted in accordance with the tenets of the Declaration of Helsinki.The informed consent was obtained from the participants before surgery and laser.

A retrospective cohort study of 60 eyes was performed with patients undergoing cataract surgery and Nd:YAG laser posterior capsulotomy postoperatively.Surgeries were performed by one surgeon (Cho YK).The inclusion criteria for patients consisted of 60 or more years of age, an axial length longer than 21.0 mm and less than 25.0 mm, clinically significant cataracts, and with postoperative Nd:YAG laser capsulotomy over 15mo of post-laser follow-up.

Phacodonesis and capsular wrinkling upon the performance of CCC were regarded as indications for CTR insertion.

The exclusion criteria were a visible area of zonulysis preoperatively and intraoperatively, previous ocular surgery,intraoperative posterior capsule rupture, and abnormal corneal topographic patterns.

In all patients, one-piece acrylic IOLs (ZCB00?; Abbot Medical Optics, Santa Ana, CA, USA) were inserted.CTRs(Ophtec, Groningen, The Netherlands) were inserted just before IOL insertion, and the choice of CTR size was made according to the severity of phacodonesis during CCC.

PCO at postoperative follow-up was measured using slit lamp microscopic examination according to the grading by Congdonet al[11]as follows: from absent (Grade 0) to severe opacity(Grade 4; central/paracentral opacity as defined above but sufficient to make the visualization of fundus details difficult or impossible).

Nd:YAG laser capsulotomy was done according to patient discomfort and the grade of PCO.The capsulotomy was tried as a cruciate pattern to make an opening size larger than the normal pupil size.

The time interval between Nd:YAG laser capsulotomy and cataract surgery was recorded, and the total YAG energy used in the capsulotomy was recorded as follows [YAG energy(mJ/pulse) × pulse number].

At 1wk, 3, 12, 15mo post-laser, the area of capsulotomy was measured, recorded, and photographed with sufficiently dilated pupils.These measurements were performed by an ophthalmologist who was blind to CTR insertion.The capsulotomy area was measured using Image J software as the percentage area of the laser capsulotomy in reference to the total corneal area.The total corneal area was defined as the area contained by the corneal limbus (Figure 1).

Figure 1 Representative picture of the calculation of the neodymium:YAG posterior capsulotomy area percentage The yellow line (A) represents the total corneal area, and the white line (B)represents the area of the capsulotomy.The capsulotomy area was measured as the percentage area in reference to the total corneal area.

As well as Nd:YAG laser capsulotomy area, ACD was compared between groups pre-laser and, 1wk, 3, 12,and 15mo post-laser.ACD was measured as the distance between the central corneal anterior surface and the anterior surface of the IOL using an A-scan ultrasound (AVISO;Carl Zeiss Meditec Ag, France).These measurements were performed by an ophthalmic technician who was blind to CTR insertion.

All patients were divided into three groups for analysis:Group 1 (No CTR group), patients that underwent cataract surgery without a CTR and with postoperative Nd:YAG laser capsulotomy; Group 2 (12 mm CTR insertion), patients that underwent cataract surgery with 12 mm CTRs and Nd:YAG laser capsulotomy; and Group 3 (13 mm CTR insertion),patients that underwent cataract surgery with a 13 mm CTR and Nd:YAG laser capsulotomy.

Statistical AnalysisSPSS Statistics for Windows software(version 11.5; SPSS Inc, Chicago, IL, USA) was used for statistical analyses.An analysis of variance test with a post hoc analysis was applied to compare data between groups.To compare the change of ACD and YAG laser capsulotomy area with the time of each follow-up visit, we used a paredt-test.To compare the frequency of PCO type and accompanied systemic disease according to each group, we used the Chisquare test and Fisher’s exact test, respectively.AP-value less than 0.05 was considered statistically significant.

RESULTS

Table 1 shows the demographics of the patients.There were no significant differences between groups in age, axial length,ACD before cataract surgery, ACD before capsulotomy, grade of PCO, type of PCO, total Nd:YAG laser energy, or time elapsed between Nd:YAG laser capsulotomy and cataract surgery.

Ⅰn the evaluation of systemic disease, five patients were with diabetes mellitus and six patients were with hypertension(Table 1).There was no definite diabetic retinopathy and hypertensive retinopathy in the slit lamp examination of fundus.We did not include the systemic status of diabetes,such as glucose level in this study, because the five diabetic patients didn’t take oral hypoglycemic therapy or insulin during the study period.The six patients with hypertension were taking aspirin during the study period with cessation for 3d before cataract surgery.

Table 1 Demographics of patients of three groups mean±SEM

Table 2 Change of ACD and capsulotomy mean±SEM

Table 2 and Figure 2 show the change in ACD in the three groups.Ⅰn Groups 1 and 2, there was no significant change of ACD in all follow-up visits 1wk and 3, 12, 15mo post-laser.Only Ⅰn Group 3, ACD change was significant 1wk post-laser compared with before Nd:YAG laser capsulotomy (P=0.048),and the significant ACD change lasted until 3mo post-laser(P=0.027).Between 3 and 15mo post-laser, there was no significant ACD change in all three groups.

Table 2 and Figure 3 show the change in the area of capsulotomy in the three groups.All three groups showed a significant increase in capsulotomy area between 1wk and 3mo post-laser (P=0.013, 0.013, 0.004, respectively).Group 3 showed a significant increase in capsulotomy area until 12mo post-laser (P=0.004).Between 12 and 15mo post-laser, all three groups showed no significant changes in the capsulotomy area.

There were no retinal IOL complications due to the enlargement of the capsulotomy opening performed in our study.

Figure 2 ACD change after Nd:YAG laser capsulotomy according to time in the three groups ACD change was significant only in group 3, 1wk post-laser compared with before Nd:YAG laser capsulotomy,and the significant ACD change lasted until 3mo post-laser.Group 1:Patients that underwent cataract surgery without CTR insertion and with postoperative Nd:YAG laser capsulotomies; Group 2: Patients that underwent cataract surgery with 12 mm CTRs and Nd:YAG laser capsulotomies; Group 3: Patients that underwent cataract surgery with 13 mm CTRs and Nd:YAG laser capsulotomies.Nd: Neodymium;CTR: Capsular tension ring; ACD: Anterior chamber depth.aP<0.05.

Figure 3 Change in the capsulotomy area (percentage) according to time in the three groups All three groups showed a significant increase in capsulotomy area between 1wk and 3mo post-laser.Group 3 showed a significant increase in capsulotomy area until 12mo post-laser.Group 1: Patients that underwent cataract surgery without CTR insertion and with postoperative Nd:YAG laser capsulotomies; Group 2: Patients that underwent cataract surgery with 12 mm CTRs and Nd:YAG laser capsulotomies; Group 3: Patients that underwent cataract surgery with 13 mm CTRs and Nd:YAG laser capsulotomies.Nd: Neodymium; CTR: Capsular tension ring.aP<0.05.

DISCUSSION

CTRs implantation can benefit cataract patients with weak zonules by maintaining the shape of the capsular bag, reducing capsule shrinkage, stabilizing IOL and reducing the incidence of PCO[3,12-13].The proposed mechanism of reduced PCO due to CTRs is that CTR may mechanically stretch the capsular bag and reduce the distance between the IOL and the capsular bag, make the posterior lens capsule completely adhered to the posterior IOL surface, inhibit LEC migrations, and reduce the development of PCO[9,12].However, there are still CTRinserted eyes with PCO, in which Nd:YAG laser capsulotomy is needed.

Nd:YAG laser posterior capsulotomy can change the anterior segment parameter in pseudophakic eyes[14-16].Also, intraocular devices, such as IOL and CTRs, can change the anterior segment parameter and the severity of PCO in pseudophakic eyes[12,17].In this study, we evaluated changes in anterior segment parameters in pseudophakic eyes with both CTRs and Nd:YAG capsulotomies.According to the study by Monteiroet al[8], YAG laser capsulotomy results in ACD deepening in eyes with IOL of C-loop acrylic hydrophobic single-piece IOL differently from the plate haptic ⅠOL.

In our study, though we inserted C-loop acrylic hydrophobic single-piece IOLs in all groups, the ACD deepening after capsulotomy was not observed in the group with Nd:Yag laser capsulotomy only (Group 1).Instead, in the group with 13 mm CTRs (Group 3), significant ACD deepening after Nd:YAG laser capsulotomy lasted until 3mo of follow-up post-laser.We suggest the following explanations: In eyes with 13 mm CTR,when posterior capsule opening occurs after Nd:YAG laser capsulotomy, the haptic offset effect of a one-piece IOL can be augmented, so the posterior compressing effect of angled,C-looped IOLs could have caused ACD deepening in Group 3,in which 13 mm CTRs mechanically stretch the capsular bag wide and reduce the distance between the IOL and the capsular bag[18-19].

According to the type of PCO, Nd:YAG laser directed towards the fibrous type of PCO needs higher energy[20]and can result in an inadvertent extension of the PCO site.However, we did not find an association between capsulotomy enlargement and PCO type.

In eyes with CTRs, there was more intracapsular force working outward, centrifugally.This force would be larger with larger diameter CTRs.With this force, which remains inside the capsule, Nd:YAG laser capsulotomy can result in extension of the capsulotomy opening.

Though we tried the lowest possible Nd:YAG energy application to get the necessary opening size using the smallest number of pulses, all three groups showed an increase in capsulotomy area between 1wk and 3mo post-laser.

Nd:YAG laser capsulotomy is a simple and easy treatment for PCO that can restore clear visual axes in a short time.However, there are several reports of complications.

Besides retinal complications after Nd:YAG laser capsulotomy,there are reports of IOL dislocation[7,21-22].

While this study evaluated only the effect of Nd:YAG laser on posterior capsulotomy, there is a recently published article to compare the circularity and centration of anterior capsulotomy and visual outcomes, according to the difference produced by different energy sources; precision pulse capsulotomy(PPC), manual-CCC (M-CCC), and femtosecond laser assisted capsulotomy (FLAC).In the future study, we are planning the evaluation of effect of CTR on the anterior capsulotomy as well as the posterior capsulotomy[23].

We assume a similar hypothesis to that made by Petersenet al[22], in which IOLs with posterior bowing were suggested to exert pressure on the posterior capsule.This pressure may exploit the capsulotomy area in the posterior capsule,especially after an Nd:YAG laser capsulotomy.In addition,the lack of fibrotic reaction between the capsules and the ⅠOL prevents the effective fixation of these lenses, especially in pseudophakic eyes in relatively earlier postoperative periods.

As we expected, in all groups, the capsulotomy opening site was enlarged until 3mo post-laser.In the group with large diameter CTRs (13 mm CTRs), the enlargement was significant until 1y post-laser due to stronger centrifugal counter force.

Between 12 and 15mo after Nd:YAG laser capsulotomy, there was no significant change in the area of the capsulotomy opening in all three groups.We suggest that the stability of the capsulotomy opening can be reached about 12mo after laser capsulotomy in pseudophakic eyes with CTRs.

This study has some limitations.The change of capsulotomy area and ACD after 15mo post-laser was not evaluated due to relatively short follow-up period in the study.The choice of CTR size was done by the surgeon’s decision according to the severity of phacodonesis during CCC which cannot be measured numerically.

ACKNOWLEDGEMENTS

Balamurali K Ambati, M.D., Ph.D.contributed to the conceptualization of this study.

Conflicts of Interest:Cho YK, None; Kim MS, None.