Phacoemulsification in posterior polar cataract

Posterior polar cataracts are white, well-demarcated, disc-shaped opacities located on the central posterior capsule and are a form of congenital cataract with autosomal dominant inheritance. Posterior polar cataract surgery is difficult for surgeons to perform because of the high risk of posterior capsular rupture, which itself stems from the opacity’s adherence to the capsule and the extreme thinness and fragility of the posterior capsule. In the present study, we evaluated the results and complications of phacoemulsification surgery in eyes with posterior polar cataracts and compared the techniques of viscodissection and hydrodissection.


INTRODUCTION
Posterior polar cataracts are white, well-demarcated, disc-shaped opacities located on the central posterior capsule and are a form of congenital cataract with autosomal dominant inheritance (1,2) .
Posterior polar cataract surgery is difficult for surgeons to perform because of the high risk of posterior capsular rupture, which itself stems from the opacity's adherence to the capsule and the extreme thinness and fragility of the posterior capsule (3)(4)(5)(6)(7) .
In the present study, we evaluated the results and complications of phacoemulsification surgery in eyes with posterior polar cataracts and compared the techniques of viscodissection and hydrodissection.
All operations were performed by a single surgeon (SC).With each patient under sub-Tenon anesthesia, a 2.8-mm clear corneal incision was made with a steel blade superotemporally, after which the anterior chamber was filled with a dispersive viscoelastic material (2% hydroxypropyl methylcellulose; Easy Visc; OphthalMed; Gre benau, Germany).After continuous curvilinear capsulorhexis, hy drodelineation was performed.Viscodissection was performed on the patients in group 1, meaning that a dispersive viscoelastic ma terial was injected into the capsule to separate the lens from the capsule and make it freely mobile.Hydrodissection was performed on the patients in group 2; then a side-port entrance was made with a 19-gauge microvitreoretinal (MVR) knife.To emulsify the nucleus, the infusion bottle was lowered to 50 cm, and low power (35%), a low vacuum (200 mmHg), and a low aspiration rate (20 cc/min) were used to minimize the stress on the posterior capsule (Sovereign Compact Phacoemulsification System; Abbott Medical Optics, Santa Ana, CA, USA).Both the aspiration of the cortex and polishing were performed from the periphery to the center, and cortex removal of the central portion was avoided even if it was not open due to the risk of capsular rupture.The capsular bag was filled with a cohesive viscoelastic material (1.6% Sodium Hyaluronate; EasyLuron; OphthalMed; Grebenau, Germany).A foldable monofocal posterior chamber IOL (Acriva; VSY Biotechnology, Amsterdam, Netherlands) was implanted into the capsular bag.After surgery, the patients received topical antibiotics four times a day and topical steroids six times a day for 1 week; the use of topical steroids was then tapered over the subsequent 3 weeks.Postoperatively, the patients were routinely examined on the first day and after the first week, first month, third month, sixth month, first year, and second year.For the statistical analysis, the postoperative values from the first month were used.
Statistical software (SPSS version 22; IBM Corporation, Armonk, NY, USA) was used for the data analysis.Data were compared using the chi-square test, Mann-Whitney U test, and Wilcoxon signed-rank test.For all statistical tests, p<0.05 was accepted as statistically significant.
Intraoperatively, posterior capsular rupture occurred during the removal of the cortex in three eyes (13%) in the group 1 patients, but vitreous loss requiring anterior vitrectomy occurred in only one eye; no rupture occurred during viscodissection in this group.Conversely, posterior capsular rupture occurred in six eyes (28.5%) in the group 2 patients; four of them occurred during hydrodissection, and two of them occurred during the removal of the cortex.Vitreous loss requiring anterior vitrectomy occurred in three eyes.Although the percentage of posterior capsular rupture was greater in group 2, the difference was not statistically significant (p=0.207).A polymethyl methacrylate sulcus fixation IOL was implanted in one eye (4.3%) in group 1 and in three eyes (14.2%) in group 2 (p=0.258).No postoperative problems were observed in these eyes.In-the-bag IOLs were implanted in five other eyes due to relatively smaller ruptures.Capsular ruptures did not affect the outcomes.In eight eyes (34.7%) in group 1 and seven eyes (33.3%) in group 2, total polar opacities could not be cleared during surgery because of firm adherence of the opacity to the posterior capsule forming a plaque (p=0.920).Nd:YAG laser capsulotomy was performed on these eyes after the third month postoperatively to prevent inflammation.
The visual outcomes were not satisfactory in two eyes (8.6%) in group 1 because of age-related macular degeneration, as well as in two eyes (9.5%) in group 2, with one resulting from age-related macular degeneration and the other from diabetic retinopathy (p=0.925).This age-related macular degeneration and diabetic retinopathy could not be detected preoperatively because of poor visualization of the fundus.In four eyes (17.3%) in group 1 and three eyes (14.2%) in group 2, postoperative vision was unsatisfactory because of preexisting amblyopia in patients with unilateral cataracts (p=0.781).Four patients (26.6%) in group 1 and four patients (28.5%) in group 2 had a family history of congenital cataracts (p=0.888).The demographic characteristics and preoperative findings of the patients are summarized in table 1. Intraoperative and postoperative findings of the patients are summarized in table 2.

DISCUSSION
Posterior capsule rupture risk during surgery is exceptionally high in posterior polar cataracts compared with other types of cataracts (5)(6)(7)(8)19,20) . The inidence of posterior capsule rupture has been reported to be between 26% and 36% (4) .In our study, this ratio was 13% in group 1 and 28.5% in group 2.
Many techniques have been described to avoid complications and minimize this risk.Using viscodissection instead of hydrodissection may protect the posterior capsule at the beginning of the surgery (9)(10)(11) .In our study, we used the viscodissection technique in the group 1 patients, which involved the injection of a dispersive viscoelastic material into the capsule to separate the lens from the capsule and make it freely mobile.We used the hydrodissection technique in the group 2 (control group) patients.No posterior capsular rupture occurred during viscodissection; however, four ruptures occurred during hydrodissection.The other ruptures occurred during the removal of the cortex in both groups.Although the percentage of posterior capsular rupture was greater in group 2, this difference was not statistically significant.The mean postoperative BCVA in group 1 was greater than that in group 2, although the difference was not statistically significant.Overfilling the anterior chamber with viscoelastic material should be avoided, the bottle height should be lowered, and the power, vacuum, and flow rate should be decreased to avoid surging and overpressurization of the anterior chamber.Removal of the cortex and polishing of the capsule should be started from the periphery toward the center.Moreover, if there is a posterior plaque firmly adherent to the capsule, postoperative Nd:YAG laser capsulotomy should be performed (12)(13)(14) .
Hayashi et al. (1) reported good results using pars plana lensectomy with IOL implantation on the remaining anterior capsule when  Ghosh and Kirkby (15) reported that planned pars plana vitrectomy, lensectomy, and posterior chamber IOL implantation can be applied to diminish the rate of posterior capsule rupture in posterior polar cataracts.
Haripriya et al. (16) described a technique in which bimanual microphacoemulsification through two 1.4-mm incisions was performed for posterior polar cataracts.In this technique, the irrigation and aspiration handpieces were interchangeable, enabling the removal of the lens fragments without hydrodissection or nucleus rotation.Nagappa et al. (17) described a modified technique for epinucleus removal in posterior polar cataracts, in which the nucleus was removed, followed by the removal of the epinucleus from the quadrant opposite to the section by aspiration using a phaco probe.Then, hydrodissection was performed to dislodge the subincisional epinucleus, which was aspirated out.Lim and Goh (18) reported a modified epinu-cleus pre-chop technique for dense posterior polar cataracts.In this technique, the anterior epinucleus is first pre-chopped, followed by the removal of the posterior epinucleus and posterior polar plaque.
Hayashi et al. (1) reported that 4 of 10 posterior polar cataract patients with a unilateral opacity exhibited amblyopia.In unilateral cases in which the posterior polar opacity entirely obstructs the pupillary area, the possibility of amblyopia is assumed to be high.In our study also, four patients in group 1 and three in group 2 with unilateral cataract exhibited amblyopia, and postoperative visual acuities were low in these patients.
In conclusion, we can minimize the complications from posterior polar cataract surgeries by being careful throughout the surgery and by using proper techniques.Viscodissection is better for avoiding posterior capsular rupture than hydrodissection.We should also remember that the incidence of preexisting amblyopia is considerable in patients with unilateral posterior polar cataracts, and patients should be warned of it, since the postoperative visual expectancies of patients are generally high.