Commentary on: Understanding IOL optic-posterior capsule dynamics

Intraocular lenses (IOLs) have evolved in terms of material and design over the years to enable implantation through small incisions, enhance biocompatibility, and minimize posterior capsular opacification (PCO).[1,2] A complete apposition between the IOL optic and the posterior capsule (PC) prevents proliferation and migration of lens epithelial cells and is postulated to be preventive against formation of PCO.[3] Postoperative PC-optic apposition has been evaluated in various studies, with a decrease in visually significant PCO and better visual quality observed in cases with complete PC-optic apposition.[4,5] Zhu et al.[4] employed Scheimpflug imaging and observed persistent PC-optic inadhesion in 41.5% cases on postoperative day 1; however, recent studies evaluating PC-optic dynamics using high resolution anterior segment optical coherence tomography suggest that residual PC-optic space is observed in 96% cases on postoperative day 1.[5] PC-optic adhesion gradually occurs in the postoperative period, with two-thirds of cases displaying complete apposition at the end of one year.[5] This complete PC-optic apposition that occurs over days to months in the postoperative period eventually impacts long-term rotational stability and helps prevent PCO. The authors have analyzed the change in PC-optic space with change in the orientation of the IOL haptic from horizontal to vertical and observed a significant decrease in the intraoperative PC-optic distance with the vertical orientation of IOL haptics.[6] The authors have not analyzed postoperative PC-optic dynamics. While the concept proposed in this manuscript regarding decreasing PC-optic distance with changing haptic orientation is interesting, it will assume clinical relevance only if the difference in PC-optic distance is significant in the postoperative period as well. At present, the recommendation for vertical orientation of IOLs is feasible only for non-toric IOLs, as majority of the toric IOLs need to be oriented along the steep corneal meridian. The authors have recommended customizing toric IOL designs, so they may be implanted with the haptics oriented vertically irrespective of the toricity; however, the commercial viability of these custom toric IOLs may be an issue. Intraoperative PC-optic space is influenced by a variety of surgical factors, including the completion of removal of ophthalmic viscosurgical devices (OVD) from behind the IOL, the amount of hydration performed at the end of surgery, and the intraocular pressure. Shallowing of the anterior chamber will decrease the PC-optic space, and injecting fluid in the anterior chamber will lead to distension of posterior capsule with increase in space. It may be difficult to ensure homogeneity of these conditions while measuring the intraoperative PC-optic distance. In addition, anatomical factors such as anterior chamber depth, axial length, capsular bag size, and white-to-white diameter will also impact the position of IOL in the bag and the relation between the IOL optic and PC. A delayed PC-optic apposition has been observed in highly myopic eyes with long axial lengths.[7] The authors have avoided extremes of axial length for the purpose of this study, and it is in fact these eyes that are more predisposed to develop postoperative IOL rotation, tilt, or decentration. The scans were first obtained in horizontal orientation, followed by vertical orientation. Rotating the IOL is expected to lead to some egress of fluid, and the motion in itself may lead to decrease in PC-optic space, which may account for the difference of 20 microns observed. Again, a difference of 20 microns may be statistically significant, but a corresponding clinical significance cannot be assumed. To conclude, prevention of PCO remains one of the benchmarks while evaluating newer IOL technologies, and we now understand that complete PC-optic apposition is essential in safeguarding against the development of PCO. Both modifiable and non-modifiable factors impact the PC-optic apposition. Non-modifiable factors include the anatomical variations in the anterior segment and the axial length of the eye. Modifiable factors are related to biocompatibility of the IOL material, IOL edge design, and surgical technique, including a continuous curvilinear capsulorhexis, 360° IOL coverage by rhexis margin, and complete OVD removal at the end of surgery. Orienting the IOL haptics vertically decreases the PC-optic distance intraoperatively; however, it remains to be seen whether the haptic orientation influences postoperative PC-optic apposition and long-term development of PCO.