Cataract surgery is the commonest surgical procedure performed worldwide with ~10 million cases carried out every year . The advent of efficient machinery and equipment, newer and more effective techniques and high quality training available for a large number of surgeons has made cataract surgery a smooth and almost complication-free surgical procedure . However, aphakia without sufficient structural support for the placement of a posterior chamber Intraocular lens (PC-IOL) in the capsular bag is a possibility following complicated phacoemulsification [3, 4], intracapsular cataract extraction (ICCE) , ocular trauma , explantation of a previous dislocated IOL, ectopia lentis (i.e. in Marfan Syndrome) and other causes of congenital or secondary zonular weakness.
A number of options exist for the correction of aphakia in the absence of capsular support, including angle-supported anterior chamber (AC) IOLs, iris-claw IOLs with anterior or retropupillary fixation and finally scleral-fixated (SF) IOLs. Angle-supported AC IOLs have been widely used for decades and have gone through years of evolution with latest open-loop designs having a much higher safety profile compared to the early designs . Open-loop AC IOLs are flexible, designed to have minimal vault as well as minimal area of contact with angle structures . With regard to iris-fixated IOLs, a variety of IOL designs and implantation modes are available, ranging from iris suturing of almost all three-piece lenses with low risk profile for UGH- syndrome due to the posterior vault of the IOL, to the even easier enclavation of specially designed iris-claw IOLs with antero- or retropupillary fixation (Figs. 1 & 2). Although retropupillary fixation has been associated with higher disenclavation rates these were later reversed when more experience was gained and more specialised instrumentation was introduced (9.7% according to a recent study)  and compare very favourably to the re-operation rate of 49% described in a large cohort of scleral-sutured IOL fixation . Moreover, retropupillary iris-fixated IOLs appear to perform equally to scleral-sutured PC-IOLs in terms of endothelial cell loss, showing no significant difference in their safety profile [12, 13]. In a retrospective comparative study between iris- and scleral-fixated IOLs , Kim et al. showed that endothelial cell loss, considered to be the most dreaded complication of AS-fixation, alongside other intra- or early post-operative complications such as intraocular haemorrhage, CMO and retinal detachment were similar between the two groups. Even in studies that reported a difference in the post-operative corneal oedema between the AC-IOL and the SFIOL group  this was transient and not evident one year post-operatively. Postoperative complication surveillance in the long term can better reflect real-life outcomes. In a study that included a much longer mean follow up of 64.1 months Chan et al.  found no statistically significant difference in post-operative complications between AC-IOL implantation and sutured SFIOL implantation.
The major advantage of iris-fixated IOLs, both angle-supported and iris-claw over scleral-fixated IOLs (SF-IOLS) has been the better visual outcome noted in the former group . The likely reason for this performance is the lack of a standardised IOL power calculation formulae for scleral fixation as opposed to well-described, audited and analysed IOL power calculation formulae for both angle-supported and iris-claw AC IOLs. Furthermore, SF IOLs have been shown to exhibit a statistically significant myopic shift compared to AC IOLs . Effective lens position estimation in the case of SF IOLs is difficult and less predictable especially in the suture-fixated subgroup depending on a number of variables such as haptic fixation distance from the limbus, presence of residual peripheral capsular structures that may displace the IOL, tightness of anchoring sutures, haptic tension, haptic angulation inducing changes in optic vault, and intrinsic anatomical ocular variations . In addition, the final IOL position following attempted scleral fixation becomes apparent only after the sutures have been tied in place and the haptics have anchored through sclerotomies, scleral canals and scleral flaps. Moreover, reposition or manipulation of an already scleral-fixated IOL might be challenging, if not impossible (i.e. in flanged or glued fixation) without risking the integrity of the haptic or optic-haptic junction and the sclera itself.
Another advantage of iris-claw and AC-IOLs is that implantation does not require any opening of the conjunctiva as opposed to PC scleral fixation, with the exception of the transconjunctival techniques (Yamane and trocar-assisted) where minimal conjunctival trauma is caused, thus avoiding unnecessary tissue manipulation that could have a negative impact on future glaucoma surgery or exacerbate pre-existing conjunctival cicatricial pathology.
As one would expect, implantation of angle-supported or iris-claw IOLs is not associated with any suture-related issues and their sequelae such as IOL tilt, decentration and even risk of vitreous haemorrhage and retinal detachment as seen in posterior or caudal dislocation. An important point that needs to be taken into account is that a lot of studies comparing different techniques are based on 12 or 18 months post-operative follow-up data; however suture-related problems may take a good few years to become apparent .
To sum up, iris-fixated IOLs, when properly sized and implanted correctly in an appropriately selected eye remain a safe and viable option with excellent outcomes (Table 1). Newer advances of AC IOL designs (i.e open-loop AC-IOLs) and fixation techniques (i.e. retropupillary iris fixation) should be assessed and compared for long term stability and other outcomes ideally through randomised controlled trials.
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Tsatsos, M., Vartsakis, G., Athanasiadis, I. et al. Intraocular lens implantation in the absence of capsular support: iris fixation. Eye 36, 1718–1720 (2022). https://doi.org/10.1038/s41433-022-02023-4