Reverse pupillary block after implantation of a scleral-sutured posterior chamber intraocular lens: a retrospective, open study

RPB is a rare postoperative complication of scleral-sutured PC IOL implantation reported by some authors [10, 11]. In addition, Khng et al [13] reported 2 eyes with intermittent pupil capture as a result of RPB. Pupil capture is an early complication of scleral-sutured PC IOL implantation, and possibly a severe or advanced form of RPB. In some of the published reports concerning pupil capture, vitrectomy was performed with scleral-sutured PC IOL implantation [10, 13‐15]. The proposed mechanism in cases with a well-positioned scleral-sutured PC IOL is posterior bowing of the iris that pushes the IOL until pupil capture occurs [10, 13]. Bading et al [15] reported pupil capture in 6 eyes (9.6%) after combined pars plana vitrectomy and scleral-sutured PC IOL implantation, and Johnston et al [14] found that intermittent pupil capture was the most common complication (9 eyes, 14.3%) in the early postoperative period. This complication is usually transient; it can be treated with pupil dilation and its recurrence might be prevented using miotic agents. However, in the study by Johnston et al. [14], 2 cases required surgical repositioning of the IOL optic. Khng et al [13] reported 2 eyes with previous vitrectomy and well-positioned PC IOL that developed intermittent pupil capture and recommended performing an Nd: YAG LPI to prevent or reduce the risk of recapture when a miotic agent is not favored or is poorly tolerated.

In our study, 2 cases of pupil capture developed and LPI was performed in these 2 eyes (Fig. 2). In case 3, we performed an IOL exchange due to malposition of a scleral-sutured PC IOL, but this patient developed dislocation of the IOL anterior to the iris on two occasions; despite repositioning of the IOL and use of pilocarpine 2% eyedrops four times per day, recurrent anterior dislocation of IOL developed, but no recurrence of anterior dislocation or pupil capture was observed after LPI. In case 4, partial pupil capture occurred twice during follow-up. Despite the use of pilocarpine 2% 4 times daily, recurrent partial pupil capture developed, but no recurrence of pupil capture was observed after LPI.

In this study, tomographic images confirmed the extremely concave iris configuration associated with RPB and allowed quantitative evaluation of the change in iris concavity, assessed by ACA measurements, before and after resolution of RPB. We speculate that the cornea could be also concave because of entrapment of aqueous humor in the anterior chamber as a result of impaired aqueous outflow before LPI and become flatter after LPI. However, the concavity of the cornea showed no significant change, which may be due to the rigidity of the cornea itself or due to the distortion of the cornea by the add-on contact lens of the OCT used for analyzing the anterior segment. The mean change in ACA was 38.21° in 7 eyes, which is slightly larger than the 33.18° reported by Higashide et al [10]. Further, the mean ACD change in the 8 eyes was 0.28 mm, which is less than the 0.47 mm in the study by Higashide et al [10], who reported that the amount of posterior movement of IOL optics varied significantly between cases, and this may be related to the design of and materials used in the IOLs. As in our study, Higashide et al [10] performed scleral-sutured PC IOL implantation 2.0 mm posterior to the limbus (the bag position) and used three-piece IOLs in all their 4 cases. This discrepancy in ACD change between the two studies may again be due to differences in IOL design. In our study, silicone IOLs were used in cases 2, 5, and 8 and acrylic IOLs in cases 1, 3, and 4, with 5° of haptic angulation for all IOLs. Cases 2, 5, and 8 had greater deepening of the anterior chamber than the other cases, possibly because the relatively less rigid silicone IOL may be more vulnerable than the acrylic IOL to being pushed posteriorly by the RPB. As well as the IOL design, a change in IOP could also be associated with a change in ACD. Despite having acrylic IOLs, cases 6 and 7 showed a greater change in ACD than the other cases, suggesting that a larger decrease in IOP may be involved.

The mean change in SE was 0.232 D in 7 eyes after resolution of RPB, which represented a statistically significant change and was much less than the 0.68 D reported by Higashide et al [10]. This indicates a less anterior shift of the IOL and may be related to surgeon preferences with regard to IOL design, surgical method used, and the suture tension of scleral-sutured PC IOL. Axial movement of an IOL can cause visual symptoms resulting from a refractive change. Using a data set of 7418 eyes, Olsen [16] found that a refractive change caused by a change in the ACD is greater in eyes with a shorter AL based on the relationship between AL and the IOL prediction error resulting from a 0.25 mm error in postoperative ACD. According to Olsen [16] a 0.25 mm change in ACD will generally cause a refractive change of approximately 0.30 D in eyes with an AL of 24.0 mm (similar to our cases) and 0.10 D in eyes with an AL of 30.0 mm. Although RPB led to relatively small hyperopic shifts in our cases, such shifts can be considerable in eyes with a shorter AL. For example, according to Olsen [16] a 1.0 mm deepening of the anterior chamber in an eye with a short AL of 21.0 mm will cause a posterior shift of 2.00 D. This shift may be symptomatic, so must be treated.

Several risk factors for RPB after scleral-sutured PC IOL implantation have been reported, one of which is a flaccid iris [9, 11, 17, 18]. A flaccid iris acts as a check valve, preventing movement of the aqueous humor from the anterior to posterior chamber and results in reverse pressure gradients across the anterior and posterior chamber [18]. Marked iridodonesis, which was present in 4 cases in our study and in one case in the study reported by Rhéaume et al [8], might suggest a flaccid iris. Flaccid iris is one of the triad of signs found in the intraoperative floppy iris syndrome (IFIS) [19] and a strong association between occurrence of IFIS and use of tamsulosin, a systemic α_1A-adrenoceptor antagonist, has also been reported [19, 20]. Although signs of IFIS were not obvious during fixation surgery in our patients, it is possible that flaccid iris was latent in 2 patients who received tamsulosin in our study. In case 3, IOL subluxation developed with extensive zonular dialysis in the right eye, despite the patient being a young man with no history of trauma. This patient was right-handed and had a habit of frequent eye rubbing. Previous studies have reported that habitual eye rubbing can induce zonular rupture and IOL subluxation or dislocation [21‐23]. Agrawal et al [24] reported a case of iridoschisis associated with lens subluxation and postulated that the lens subluxation precipitated iridoschisis by mechanical rubbing of the back of the iris, which may be associated with flaccid iris.

Some authors have argued that in the vitrectomized eye, in conjunction with a flaccid iris, RPB after scleral-sutured PC IOL implantation is caused by increased flow of aqueous humor from the posterior chamber and the vitreous cavity to the anterior chamber with movement of the eye due to the absence of the lens capsule, the lens zonular fibers, and the vitreous [9, 11]. In our study, all cases had partial vitrectomy or pars plana vitrectomy and may have developed RPB via this mechanism. Further, some studies have reported that high axial myopia might also be a cause of RPB [9, 11, 14]. A highly myopic eye tends to have a greater posterior chamber volume, leading to more aqueous humor flowing into the anterior chamber and a flaccid iris, but this has not yet been established [9]. All cases in our study had a relatively long axial length.

In our study, all cases showed angle pigmentation at preoperative gonioscopy. Interestingly, all cases in our study had severe preoperative zonular dialyses; consequently we should have performed scleral sutured PC IOL implantation instead of the in-the-bag placement, even with the support of a capsular tension ring. Mechanical factors such as crystalline lens or IOL tilt and variable axial position due to zonular weakness might induce contact between the crystalline lens or IOL optic and the middle posterior iris pigment epithelium, leading to release of pigment. This accumulated pigment might contribute to impaired aqueous flow through the trabecular meshwork, and resistance to aqueous outflow might be a risk factor of RPB. A squared-edge IOL design has been reported to be a risk factor for chafing of the iris in the absence of the lens capsule [25‐27] but preoperative angle pigmentation was not aggravated by IOLs with a squared-edge design after scleral-sutured PC IOL implantation in our study.

Considering all potential risk factors together, in circumstances of impaired aqueous outflow due to angle pigmentation, increased flow of aqueous humor from the posterior chamber and the vitreous cavity to the anterior chamber might cause entrapment of aqueous humor in the anterior chamber, followed by RPB due to back bowing of a flaccid iris after scleral-sutured PC IOL implantation, especially in an eye that is vitrectomized and/or has a long axial length.

LPI has been reported to be effective in relieving RPB after scleral-sutured PC IOL implantation [8‐11]. All of the patients in our study responded immediately to LPI, with significant improvements in vision, IOP, and other biometrics. Contrary to the characteristic posterior-to-anterior rush of fluid immediately after LPI in traditional relative pupillary block, the breakthrough fluid rush in RPB is in the reverse direction. Physiologically, with this stasis of aqueous humor in the anterior chamber, whereby differential pressures exist between the anterior and posterior chambers, creation of an iridotomy allows rapid resolution of RPB, as the pressures across the anterior and posterior segments then freely equilibrate.[4] This restores the planar configuration of the iris, relieving posterior bowing and RPB [4, 28‐30]. Our post-LPI tomographic and Scheimpflug images revealed successful flattening of the iris and widening of the space between the posterior iris and IOL. This was noted to be secondary to the forward shift of the iris and the stable IOL position in the posterior chamber after treatment. In addition, all measurements in our study, including CDVA, IOP, ACA, ACD, and SE, showed a statistically significant improvement after LPI and demonstrated the efficacy of LPI.

The main limitation of this study is that we did not carry out a comparison with a control group of eyes that underwent scleral-sutured PC IOL implantation but did not develop RPB. RPB has been considered a rare postoperative complication after scleral-sutured PC IOL implantation. Further investigations, including a case–control study, may be necessary to calculate a risk ratio based on the risk factors and address the incidence of RPB after scleral-sutured PC IOL implantation. However, most of the increased IOP or pupil capture might occur via the above-mentioned mechanisms and RPB might be an underestimated phenomenon rather than a rare one. Additionally, there were no specific presenting symptoms in our cases, except 2 pupil capture cases that presented with blurred vision only; the RPBs were diagnosed only on regular follow-up. Routine postoperative examination of IOP and ACD using anterior segment optical coherence tomography or Scheimpflug imaging can be considered. In addition, in patients with a high preoperative IOP and severe angle pigmentation on gonioscopy, preoperative or intraoperative evidence of a flaccid iris and a long AL, a careful, meticulous anterior vitrectomy, if necessary, should be performed during surgery, given the risk for RPB. In these patients, intraoperative prophylactic peripheral iridectomies using a vitreous cutter or postoperative LPI may prevent the complications induced by RPB, such as increased IOP, pupil capture, positional instability of the IOL, and refractive change.