Our study shows that the main indications for IOL exchange are IOL displacement (subluxation or decentration) followed by corneal decompensation.
Over the last decades, indications for IOL exchange have been changed. It seems that refractive surprise, corneal decompensation, and IOL opacification were more common in the early 20s, while IOL dislocation became more prevalent later. In a study evaluating patients from the 1990s, a period of rapid development in lens technology and surgical techniques, the most common indication for IOL exchange or removal was bullous keratopathy.[3] In, two studies evaluating IOL exchange surgeries performed in the 2000s reported the most frequent indications as refractive errors and IOL opacification.[4, 5] In a study by Jin et al.[10] evaluating cases between 1998 and 2004, the most common indication for IOL exchange was incorrect IOL power calculation (41%), whereas in a similar study by Lyle and Jin.[11] the most common indication for IOL removal was corneal decompensation (38%). In a study between 2002 to 2017 on 492 eyes, IOL opacification was the first indication (138 − 28%), followed by IOL dislocation (80 − 16%).
Jones et al.[6] evaluated IOL exchanges between 2007-and 2011 and reported that IOL dislocation was the indication in 46% of the surgeries. similarly, we found IOL malposition as the most common indication for lens exchange in 50.30% of eyes.
Subluxation or dislocation of the lens-capsule complex can occur years after an uncomplicated surgery due to progressive separation of the zonules associated with various causes such as PEX, retinitis pigmentosa, and long axial length. In a multi-center study, Pueringer et al.[13] analyzed nearly 15,000 cases who underwent cataract surgery within about 30 years to evaluate the risk of late IOL dislocation. They reported the risk of IOL dislocation as 0.1% at ten years and 1.7% at 25 years. Davis et al.[14] evaluated cases with spontaneous IOL dislocation who underwent IOL repositioning and reported that the presence of PEX was the most critical risk factor for lens dislocation, followed by previous vitreoretinal surgery and trauma.
Patients with PEX are at higher risk of intraoperative complications like posterior capsular rupture (PCR). Jones et al.[6] reported that in PEX patients with dislocated IOL, 40% had a ruptured posterior capsule intraoperatively, the posterior capsule was opened in 10% with YAG laser capsulotomy, and the others had intact posterior capsules.
With technological advancements, open-loop, flexible anterior chamber IOLs have become a lens replacement option that provides good visual outcomes. Jin et al.[10] reported that a visual acuity better than 20/40 was achieved in 90% of patients who received an anterior chamber IOL. In a study by Kwong et al.[15] comparing anterior chamber and scleral-fixated IOLs in patients with inadequate posterior capsule support, scleral-fixated IOLs were associated with lower rates of intra- and postoperative complications. In contrast, anterior chamber IOLs resulted in better final visual acuity outcomes.
In the current study, corneal decompensation was the second most common indication for IOL exchange. Duran et al.[16] evaluated the indications for and outcomes of 29 cases undergoing anterior chamber IOL explantation and reported that corneal decompensation was the indication for IOL explantation in 22 cases. Three of those underwent keratoplasty and scleral-fixated IOL implantation; no surgical intervention was performed in the remaining cases. PCIOL displacement is divided into two types; in the bag: the subluxation and dislocation of IOL in the capsular bag or out of the bag when the IOL is placed in the sulcus. Ten (5.2%) of our patients were extracapsular, and 87 (45.1%) were intracapsular. Hayashi et al.[17] evaluated the predisposing factor for lens dislocation separated by the intracapsular and extracapsular classification. The most predisposing factor for intracapsular dislocation were PEX (17.38–44.7%), retinitis pigmentosa (4.38–10.5%), status after vitrectomy (2.38–5.3%), trauma (2.38–5.3%), and long axial length (2.38–5.3%). The hypothesized mechanism for this type of dislocation is insufficient zonular strength or gradual degradation.
The factors associated with extracapsular dislocation were secondary IOL implantation (11/24 -45.8%), surgical complications (3/24 -12.5%), mature cataract (3/24 -12.5%), and PEX (2/24 − 8.3%), respectively. The time interval for exchange surgery was significantly shorter for those with intracapsular dislocation (p = 0.0006). The visual outcome of the two groups did not reveal a significant difference between the two study groups.
Similar to our series, the most common complications after IOL exchange are CME, dislocation of the secondary implanted IOL, corneal edema, RD, and glaucoma.[17]
IOL explantation can be performed from the anterior or pars plana approach. All patients were explanted through the anterior approach in our series because the patients needing concomitant VR surgery were excluded from this study. In a review by De Rajos et al.[18] the surgical approach for IOL explantation was anterior in 104 cases (73.75%) and posterior in 37 (26.24%). Vitrectomy was performed concurrently with IOL removal in 135 cases, from a limbal approach in 98 cases, and pars plana vitrectomy in 37 cases. Two groups were comparable in terms of visual outcome and postoperative complications.
The time interval between the first surgery and IOL explantation was 4.12 ± 5.6 in our series, which is comparable with most studies. De Rajos et al.[18] reported the average time from original surgery to IOL explantation was 7.89 ± 5.81 years (range 0.08 to 29); 9.31 ± 7.54 years (range 0.75 to 29) for anterior chamber IOLs, and 7.70 ± 5.55 years (range 0.08 to 28.25) for posterior chamber IOLs (p = 0.529) There was no significant difference between the in-the-bag, the out-of-the-bag IOL dislocation group. In the study by Vounotrypidis et al.[19] the mean period between the primary surgery and the secondary IOL implantation was 8.4 ± 6.5 years (range 0 − 32 years). Goemaere et al.[20] reported that the shortest time interval is in refractive error (29.42 ± 42.46 months), and the most prolonged time is for corneal decompensation (151.83 ± 111.07 months).
There are various surgical options to implant the secondary IOL, including anterior iris-claw IOLs, scleral or iris-fixated IOLs, and retropupillary fixation of iris-claw IOLs.
The choice of IOL depends on the availability of IOLs, the status of the posterior capsule and iris, and the surgeon's experience and preference. In a report by De Rajos et al.[18] retropupillary iris-claw IOL was used in most patients with a favorable outcome. While angle-supported IOLs were implanted in half of the patients in the study by Vounotrypidis and colleagues.[19]
Iris claw AC-IOL was the most commonly used secondary IOL in our series, followed by scleral-fixated PCIOL.
Various factors affect the visual outcome after IOL exchange. Postoperative astigmatism due to the lens tilt and incidence of postoperative complications, including IOP rise, RD, or corneal decompensation, limit visual acuity improvement after IOL explantation. The high rate of corneal decompensation could be attributed to the present protocol of our center, in which patients with the clear cornea and abnormal endothelial cell counts did not undergo concomitant keratoplasty.
The retrospective nature of the disease limits our study. Incomplete data in some patients, surgery by different surgeons, and loss of follow-up in some patients are among the other limitations of the present study. However, this study reports a large series with an extended follow-up.
In conclusion, IOLs implantation may require further surgical intervention to prevent more damage to the eye or restoration of visual function. This intervention's causes are different regarding population characteristics, type of IOL (PC vs. AC), and the study time. In the current research, complications of previous surgery lead to the displacement of the IOL in PC IOL, and corneal decompensation in AC IOL was the most common cause for secondary surgical procedures. The main side effects of second surgery in the current study were glaucoma, CME, RRD, and corneal decompensation.