Phakic intraocular lenses: Where are we now?

The correction of a refractive error can be performed via a subtractive procedure, such as using an excimer laser or a refractive lens exchange (RLE), or as an additive procedure, such as placement of phakic intraocular lenses (pIOLs) or corneal inlays. Of these options, pIOLs are now considered a safe and predictable alternative to laser corneal refractive surgery when treating moderate to high myopia, in particular when the end goal is the retention of the patient’s ability to accommodate.1–3 The 3 available pIOL types—angle-supported and iris-claw anterior chamber and posterior chamber—offer surgeons different specifications that they must match against their patients’ needs and desired visual outcomes.1–7 The history of pIOL development is informative in understanding the current situation. Strampelli implanted the first minus-power angle-supported anterior chamber pIOL in 1953. Initial study results from Barraquer were encouraging; however, complications such as chronic endothelial cell loss (ECL) and iris retraction led to high levels of pIOL explantation. Progress was made in the 1980s and 1990s in reducing complications, but the fast pace of development led to safety concerns, which led to the withdrawal of some designs from the market.1,4,5 The iris-fixated anterior chamber pIOL also has roots in the 1950s, when IOLs originally designed for aphakic eyes were developed. Notable models included the Binkhorst and the Medallion IOL.1 In 1978, Worst designed the iris-claw IOL, again for aphakic eyes.3,4 In 1986, Fechner and Worst implanted an IOL in the first sighted myopic phakic eye with good predictability outcomes; however, there was progressive ECL of approximately 7%.1 Current models are still based on the original design.1,4,8 In 1986, one of the first posterior chamber pIOLs, the “collar-button” or “mushroom” design, was developed and attributed to Fyodorov. This single-piece posterior chamber silicone pIOL had a 3.2 mm optic and a concave anterior surface that projected anteriorly through the pupil. Since then, several posterior chamber models have been released on the market.1 Although laser refractive surgery remains the treatment of choice for patients seeking spectacle independence, it is not suitable in all cases. Patients with moderate to high myopia often require a different approach as the accuracy of laser refractive surgery declines as myopia increases with the added likelihood of negative outcomes, including halos, glare, and ectasia.5 Implanting pIOLs offers the best chance of maintaining the best-corrected visual acuity in these circumstances.9 In many studies, the quality of vision in patients with high myopia has been reported to be better after pIOL implantation than after laser in situ keratomileusis (LASIK).2,5,8–11 Standard reporting guidelines for refractive outcomes of IOL-based refractive surgery, corneal laser surgery, and RLE used by some journals12–14 provide comparative information for models and techniques and enables conclusions to be drawn on comparable safety and efficacy.12 Analysis of the European Registry of Quality Outcomes for Cataract and Refractive Surgery database between 2004 and 2014 showed that pIOLs had comparatively good reported visual outcomes, in particular compared with LASIK.6 Furthermore, a Cochrane Review by Barsam et al.9 found that pIOLs were more accurate and safer than excimer laser surgical correction for moderate to high myopia in the range of −6.0 to −20.0 diopters (D), leading to pIOL implantation being the accepted clinical treatment for higher levels of myopia (spherical equivalent ≥6.0 D) with or without astigmatism. This, in turn, led to the introduction of treatment protocol guidelines for the implantation of pIOLs.15 In the absence of contraindications, pIOLs represent a good option for experienced surgeons.1,2,4,7,8 All pIOL models have several advantages in common, including rapid visual recovery, excellent refractive stability, improved visual acuity, no removal of ocular tissue, retention of accommodation, and reversibility.5,9,16,17 Small incisions, approximately less than 3.0 mm, and the rotational stability of toric pIOL models allow for fast visual rehabilitation.18,19 On the whole, complications are rare and dependent, to a large extent, on the location and placement of the pIOL given that they are by design additive and introducing foreign materials into the eye can lead to intraocular tissue injuries or block the outflow of aqueous from the chamber, resulting in increased eye pressure.15,20 For anterior chamber IOLs, the main concern, especially in the long term, is ECL resulting from the IOL’s proximity to the corneal endothelium.9,10,21–23 With its important role in maintaining the cornea, severe ECL can lead to stromal edema and bullous keratopathy.11 Other side effects include pupil ovalization, chronic inflammation, and cataract formation.3,11 A study of the complications of an angle-supported foldable pIOL (Acrysof L-series Cachet) that assessed 638 patients (1087 eyes) 10 years after implantation found a persistent decrease in endothelial cell density (ECD) in some eyes at higher than expected rates16 (typically 0.6% ± 0.5% [SD]).11,24 The outcomes indicated that ECL resulted in only 3.1% of all implanted pIOLs being explanted and no permanent loss of vision. Regular monitoring was recommended24; however, the results were contrary to the initial positive results2 and the increased risk for pIOL explantation led to the voluntary removal of that pIOL from the market. Interestingly, due to the limited understanding of the causes of ECL, the study found that the conclusions drawn could have been a result of outlier characteristics and not the pIOL design.24 My conclusion was that these results demonstrated the best value for anterior chamber pIOLs in terms of ECL, nevertheless the IOL was removed from the market! Tahzib et al.11 found that the refractive stability of iris-supported anterior chamber pIOLs was maintained without late-onset complications or long-term ECL over a 10-year study period (reported ECD 3.62% ± 16.97% at the 10-year follow-up). However, positive outcomes are dependent on strict inclusion criteria and meticulous surgical technique. The study reported visual acuity outcomes comparable to the long-term results of myopic photorefractive keratectomy in myopic patients.11 Other long-term follow-ups of anterior chamber pIOLs yielded similar visual outcomes. Implantation of the Artisan myopia claw iris-fixated pIOL (Ophtec BV) resulted in a substantial loss of ECD between 3 years and 7 years,22 with Jonker et al.25 reporting long-term changes in ECD after the implantation of the myopia and toric iris-fixated models. The total chronic ECL was 16.6% and 21.4% from 6 months to 10 years, respectively, in each group, 6.0% and 4.8% of cases, respectively, required explantation because of ECL. Because preoperative age-related ECD is a risk factor for increased ECL,4 Jonker et al.25 recommended higher thresholds of preoperative age-related ECD to ensure the cornea can tolerate future cataract surgery and pIOL explantation. The complications associated with the early anterior chamber angle-supported pIOLs led to a movement toward the use of posterior chamber pIOLs at the end of the last century. Theoretically offering a lower incidence level of halos, glare, and damage to the corneal endothelium, they gained popularity; however, complications remained including a higher rate of cataract formation and pigment dispersion and, for some models, cortical opacities and decentration.1,21,22 Lens subluxation and intraocular pressure (IOP) rise are also concerns, although less so with modern designs.20 The new Implantable Collamer Lens pIOL design with a central hole seems to have greatly reduced these complications, in particular. This is because the central hole enables aqueous flow, significantly reducing cataract formation. Shimizu et al.16 found that the newer pIOL with a central hole (V4c) performed as well as the conventional pIOL (V4b) over a 5-year period in terms of safety, efficacy, predictability, and stability, especially in IOP and ECD. No eye required an neodymium:YAG iridotomy or intraoperative iridectomy, and the levels of cataract formation were lower.17 Endothelial cell loss 5 years postoperatively was 0.5% ± 5.4% and 1.2% ± 7.2% with the central hole pIOL and conventional pIOL, respectively, with no significant decrease in ECD (>15%).16,17 Other aspects of pIOL implantation also require further research. In this issue, Kohnen et al. (pages 124–128) describe a technique for the successful application of femtosecond laser–assisted cataract surgery in eyes with cataract and previous implantation of both anterior pIOLs and posterior chamber pIOLs. Although caution should be exercised when dealing with posterior chamber pIOLs, this technique has the potential to offer lower levels of endothelial cell reduction than conventional cataract surgery. This indicates that femtosecond laser–assisted cataract surgery have benefits over manual cataract surgery in eyes with pIOLs implantation. Overall, the future looks positive for pIOLs. In some parts of the world, pIOLs have become the preferred method to treat refractive errors. Initial studies have indicated that pIOL surgery is safer than excimer laser surgical correction for moderate to high myopia,4 but there is still a lack of long-term data. Although concerns about long-term visual outcomes are beginning to be addressed, there is still a need for longer term studies of the impact of pIOLs and associated complications.9,17,20,22,26