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REVIEW/UPDATE

Middle- and long-term results after iris-fixated phakic intraocular lens implantation in myopic and hyperopic patients

a meta-analysis

van Rijn, Gwyneth A. MD; Gaurisankar, Zoraida S. MD; Ilgenfritz, Antonio P. MD; Lima, José Eduardo E. MD; Haasnoot, Geert W. PhD; Beenakker, Jan-Willem M. PhD; Cheng, Yanny Y. Y. MD, PhD; Luyten, Gregorius P. M. MD, PhD

Author Information
Journal of Cataract & Refractive Surgery: January 2020 - Volume 46 - Issue 1 - p 125-137
doi: 10.1097/j.jcrs.0000000000000002
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When it comes to the correction of high myopia and hyperopia, the advent of phakic intraocular lens (pIOL) implantation and its improvements in methods and materials were a breakthrough. Inspired by Harold Ridley, Kees Binkhorst, Svyatoslav Fyodorov, and Klaas Otter, among other pioneers in the field of IOLs, Jan Worst introduced an IOL that attached to the iris. In 1978, he implanted the first iris-claw lens for aphakia after cataract surgery. In 1984, an opaque iris-claw lens was implanted in a phakic eye for pupil occlusion to relieve complaints of intractable diplopia. During an ophthalmology meeting in 1986, Worst developed the idea of a “contact lens in the eye.”A On November 2, 1986, Worst and Fechner implanted the first-generation biconcave iris-fixated pIOL (ref. 209) in a myopic eye of −20 diopter (D).A The name of the iris-fixated pIOL was changed from Worst iris-claw or lobster-claw lens to Artisan lens. This name was chosen to honor the special skills of Dr. Worst.1 Despite the positive visual and refractive results, unacceptable complications occurred and the biconcave Artisan was discontinued.1,2 In 1991, a convex-concave–shaped design (ref. 206) to create more distance from the edge of the iris-fixated pIOL to the corneal endothelium was introduced and has been implanted successfully since. The first iris-fixated pIOL for the correction of hyperopia (ref. 203) was released in 1993 and first implanted by Krumeich in April 1993, and Worst in early 1994. In 1997, an iris-fixated pIOL for myopia was developed, with a larger optic diameter (ref. 204) to reduce optic phenomena such as glare and halos.

The modified convex-concave–shaped Artisan iris-fixated pIOL (Ophtec) has been in use since 1998. In 2004, the U.S. Food and Drug Administration approved the use of the Artisan and the identical Verisyse (Abbott Medical Optics, Inc.), and the Artisan/Verisyse iris-fixated IOL has found global acceptance. The iris-fixated pIOL is available in refractive powers ranging from −3.0 to −23.5 D in 1.0 D increments before 1997, and after 1997 in 0.5 D increments. The Artisan Small (ref. 202), which was made available in the year 2000 for eyes with proportionally reduced dimensions of the anterior chamber, is no longer available.

Since the iris-fixated pIOL has been marketed for more than 25 years, an assessment of the long-term effects after implantation of this pIOL for refractive errors seems called for. In this systematic review and meta-analysis, we searched the literature for articles on the middle- and long-term effects (from 2 to 10 years) of the iris-fixated pIOL, to provide a clear picture of the results and risks of implantation.

METHODS

We applied the tenets of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement. The databases PubMed, EMBASE, Web of Science, and Cochrane Library were searched; no time limit was used for the search. Figure 1 shows the eligibility and exclusion criteria. The 4 databases were last searched on the following dates:

  1. PubMed on August 3, 2018, yielding 539 references;
  2. Web of Science (Thomson Reuters) on August 28, 2018, yielding 476 references;
  3. EMBASE on August 28, 2018, yielding 586 references;
  4. Cochrane Library on August 28, 2018, yielding 42 references.
Figure 1
Figure 1:
Eligibility and exclusion criteria (IF-pIOL = iris-fixated phakic intraocular lens).

Although foldable iris-fixated pIOLs (ie, Artiflex/Veriflex) were an exclusion criterion, the terms “Artiflex” and “Veriflex” were included in the search to avoid missing any relevant articles. Search strings can be found in Appendix 1 (see Supplemental Digital Content 1, available at http://links.lww.com/JRS/A1). The search strategy was developed by an information specialist in consultation with the researchers. No restrictions were placed on the levels of evidence required for inclusion in the search because it was expected that most studies would be of observational nature.

All 1643 references were then uploaded in a citation manager (EndNote X7) for organization purposes. After checking for and removing duplicates, a total of 750 unique references remained. The title and abstract of every unique publication were analyzed. Two researchers (G.R., A.I.) independently screened and selected the articles retrieved by the search, the results were compared, and disagreements were resolved by discussion; if necessary, a third party was invited to the discussion. References that met any of the established exclusion criteria were excluded. The assessment of the full texts and bibliographies of 137 articles resulted in 32 studies being included in this review and meta-analysis.3–35 Relevant articles in which complications were reported as case series but no incidence could be calculated are not listed in the Results section but are still included in the Discussion section.35–37

The bibliography of each eligible reference was searched manually for additional articles that may not have been identified previously by our systematic search. No further articles were found at this stage. However, 1 additional reference that was not included in the databases was found through a simple web search.30 See Figure 2 for the selection process. All relevant information was extracted from each reference and recorded in the spreadsheet software (Microsoft Excel 2010; Microsoft Corp.). Statistics for pooled estimates were performed in IBM SPSS Statistics for Windows software (version 23, IBM Corp.). Studies in which eyes underwent additional corneal refractive surgery were reviewed but were excluded from the meta-analysis for refractive and visual acuity outcome measures. Data on visual acuity were converted to logarithmic of the minimum angle of resolution for calculation purposes. Charts and figures were assembled using either SPSS or Excel.

Figure 2
Figure 2:
Selection process (IF-pIOL = iris-fixated phakic intraocular lens).

RESULTS

The selected studies comprised 5523 myopic eyes and 162 hyperopic eyes. The sample sizes in the articles range from 26 to 1140 myopic eyes and from 14 to 136 hyperopic eyes. Twenty-nine articles describe the results after iris-fixated pIOL implantation in myopic eyes.3–18,20–32 Four articles describe the results after iris-fixated pIOL implantation in hyperopic eyes.19,20,32,33

In most of the studies, not all participating patients reached the last follow-up visit, and the number of examined patients varies from one follow-up period to another. The mean age at the time of iris-fixated pIOL implantation ranges from 22 to 51 years in the myopic study groups and from 32 to 44 years in the hyperopic study groups.

All 32 studies were reviewed and are summarized in the Appendices (see Supplemental Digital Content 1 to 5, available at http://links.lww.com/JRS/A1, http://links.lww.com/JRS/A2, http://links.lww.com/JRS/A3, http://links.lww.com/JRS/A4, and http://links.lww.com/JRS/A5). In two studies, a significant percentage of eyes had additional corneal refractive surgery32,33 and were excluded from the pooled estimate calculations for refractive outcome and visual acuity.

Type of Iris-Fixated pIOL

Of all studies selected, 1 study included only the Artisan 6/8.5,30 and 2 studies included only the Artisan 5/8.5.3,23 Four studies report on results after the implantation of the Artisan Hyperopia,19,20,32,33 and 1 study included the Artisan Myopia Small 5/7.5.14

Refractive Outcome

Refractive outcome may be presented as changes in the manifest refractive spherical equivalent (MRSE) and deviation in the MRSE from the targeted refraction.

Changes in the MRSE

Fifteen studies with a total of 1400 eyes report on changes in the MRSE in myopic eyes. Two studies do not specify the follow-up period of the reported MRSE data. The preoperative pooled MRSE ranges from −18.9 to −10.4 D (median −13.3 D), and the postoperative pooled median MRSE ranges from −0.8 to −0.4 D at various follow-up times (see Table 1). The MRSE per study is summarized in Appendix 2 (see Supplemental Digital Content 2, available at http://links.lww.com/JRS/A2).

Table 1
Table 1:
Pooled estimates of changes in the MRSE preimplantation vs postimplantation of an iris-fixated phakic IOL in myopic eyes.

Two studies report on changes in the MRSE in hyperopic eyes. In the study by Guell et al.,32 41.4% of the eyes were treated with a combined pIOL implantation and additional corneal refractive surgery. In the study by Saxena et al.,19 the preoperative MRSE was 6.80 D, and the postoperative MRSE was 0.10 D at 3-year follow-up (see Table 2).

Table 2
Table 2:
Changes in the MRSE in hyperopic eyes preimplantation vs postimplantation of an iris-fixated phakic IOL in hyperopic eyes.

Changes in the MRSE during follow-up periods are described as being not significant. However, only a limited number of studies have statistically proven this.4,12,13,15–17,23,28,31 Changes in the MRSE per study are graphically plotted against time in Figure 3.

Figure 3
Figure 3:
Scatterplot of published data on change in the manifest refractive spherical equivalent.

Deviation in the MRSE From Target Refraction

Fourteen studies with a total of 1602 eyes report on the percentage of myopic eyes within 1.0 D of the targeted refraction. Ten studies report on the deviation in the postoperative MRSE from emmetropia; 4 studies report on the deviation from the intended (calculated) correction.

The percentage of eyes within 1.0 D of emmetropia ranges from 55% to 98%. The overall pooled median of eyes within 1.0 D of emmetropia is 94% (all follow-up periods). A slightly smaller range of 65% to 93% of eyes are within 1.0 D of the intended correction. The overall pooled median of eyes within 1.0 D of the intended correction is 78.8% (all follow-up periods). See Tables 3 and 4 and Appendix 2 (see Supplemental Digital Content 2, available at http://links.lww.com/JRS/A2). Two studies report on hyperopic eyes combined with additional corneal refractive surgery.32,33 Details are given in Appendix 2 (see Supplemental Digital Content 2, available at http://links.lww.com/JRS/A2).

Table 3
Table 3:
Pooled estimates of the MRSE within the range of emmetropia in myopic eyes (%).
Table 4
Table 4:
Pooled estimates of the MRSE within the range of intended correction in myopic eyes (%).

Visual Acuity

Uncorrected (UDVA) and corrected (CDVA) distance visual acuity, safety index (SI), and efficacy index (EI) are common parameters to assess the effect of the iris-fixated pIOL on visual acuity; details are in Appendix 3 (see Supplemental Digital Content 3, available at http://links.lww.com/JRS/A3).

UDVA and Efficacy

Data on UDVA are commonly reported as the cumulative percentage of eyes within a visual acuity range. Efficacy can be described as the percentage of eyes achieving a postoperative UDVA of 20/40 and 20/20 or better. The pooled median of the percentage of myopic eyes with a UDVA of 20/40 or better is 87% and 82% at 2- and 5-year follow-up, respectively. The pooled median of the percentage of myopic eyes with a UDVA of 20/20 or better was 35% and 21% at 2- and 5-year follow-up, respectively (see Table 5).

Table 5
Table 5:
Pooled estimates of UDVA in myopic eyes.

The EI reflects the ratio between the preoperative CDVA and postoperative UDVA: (mean postoperative UDVA)/(mean preoperative CDVA). The pooled median EI at 2, 5, and 10 years is 0.90, 1.02, and 0.80, respectively (Table 6). Efficacy indices have a wide range from 0.43 to 1.03; only Silva et al.17 describe an EI of below 0.8. They note a slight undercorrection immediately postoperatively but give no explanation.

Table 6
Table 6:
Pooled estimates of the efficiency index and safety index in myopic eyes.

Only Qasem et al.33 report on a small number of hyperopic eyes, with 100% having a UDVA of 20/30 or better at 2- and 3-year follow-up and 28.6% of eyes having additional corneal refractive surgery after iris-fixated pIOL implantation. Efficacy indices are 0.81 and 0.9 at 2 and 5 years, respectively, as reported by Guell et al.,32 with 41.4% of eyes having additional corneal refractive surgery after implantation.

CDVA and Safety

Data on CDVA are often reported as the change in visual acuity preimplantation vs postimplantation; 14 studies report on changes in CDVA in myopic eyes (Table 7). All studies report that more than 91% of myopic eyes have a stable or a gain in CDVA. The pooled median postoperative CDVA increased compared with the preoperative CDVA to 0.05, 0.02, and 0.12 logarithmic angle of minimum resolution units at 2, 5, and 10 years of follow-up, respectively, which equals 0.89, 0.96, and 0.76 Snellen (Table 8). Nine studies report on a loss of 2 or more lines of CDVA in up to 4.5% of the eyes.4,5,7,12,13,15,27,28,33 The primary reason for a loss of 2 or more CDVA lines is cataract (9 eyes) (Table 7).

Table 7
Table 7:
Safety in myopic eyes, change in lines of CDVA.
Table 8
Table 8:
Pooled estimates of CDVA in myopic eyes.

The SI is defined as the ratio of (mean postoperative CDVA)/(mean preoperative CDVA). All reported safety indices for myopic eyes are above 1.0. The pooled median SI at 2, 5, and 10 years of follow-up is 1.19, 1.10, and 1.10, respectively (see Table 6).

Although no specific number is given by Qasem et al.,33 no hyperopic eye lost a line of CDVA. Saxena et al.19 describe a CDVA of 0.75 at 3-year follow-up, with 50% of hyperopic eyes having a stable or a gain in CDVA. A SI of 0.95 and 1.25 is reported by Guell et al.32 at 2- and 5-year follow-up, respectively.

EC Loss

Most studies report on EC change from baseline. Other articles report on EC change from 6 months to 1 year after implantation, attempting to describe chronic EC change by excluding the acute EC loss induced by surgery. Some articles only report the yearly percentage of EC loss, some only on absolute EC counts, and others on both. Details per study are in Appendix 4 (see Supplemental Digital Content 4, available at http://links.lww.com/JRS/A4).

Various conclusions on EC change are drawn by the different authors, ranging from a gain in EC10,23,31 to no significant EC change or a significant EC change over the follow-up period. For the pooled estimates of absolute EC change given in this article, a linear decrease in EC over time is assumed, as in the reviewed articles. Saxena et al.21 and Qasem et al.33 (2- and 3-year follow-up) are excluded from the pooled estimates because the reported EC change in these studies included different types of iris-fixated pIOLs.

Twenty-three articles on myopic eyes report on EC change in the period of 2 to 4 years after implantation, ranging from a small gain of 0.26% to a loss of 14.58%.3–7,9–13,15–18,21,22,24,27–30,32 Twelve articles on myopic eyes report on EC change in the period of 5 to 7 years after implantation, with a range of 0% to 15.6% EC loss.6,7,12,16–18,21,23,26,29,30,33 Four studies report on a follow-up period of longer than 7 years, with EC loss ranging from 4.9% to 22.5%.6,23,26,30 The number of eyes examined at given follow-up periods per study ranges from 6 to 293. Pooled estimates for the percentage of the annual EC change per follow-up period are presented in Table 9. The overall median annual EC loss is 60 cells/mm2 (ranging from −96 to 144 cells/mm2). Figure 4 shows a stem-and-leaf plot of the overall annual EC loss and median annual EC change per study.

Table 9
Table 9:
Pooled estimates of EC change in myopic eyes.
Figure 4
Figure 4:
Stem-and-leaf plot annual EC change (ACD = anterior chamber depth; EC = endothelial cell).

Two studies on hyperopic eyes report on EC change in the period of 2 to 4 years, ranging from 5.4% to 11.7%.19,32 The number of examined eyes ranges from 10 to 35. Pooled estimates for the percentage of the annual EC change per follow-up period are presented in Table 10. In Figure 5, absolute EC counts are plotted against time for both groups. The overall median annual EC loss is 65.5 cells/mm2 (ranging from 44 to 93 cells/mm2; see also Figure 4).

Table 10
Table 10:
Pooled estimates of endothelial cell change in hyperopic eyes.
Figure 5
Figure 5:
Scatterplot of reported absolute endothelial cell changes.

A variable minimum anterior chamber depth (ACD) was used as a selection criterion, ranging from 2.6 to 3.2 mm across the various studies. There seems to be no difference in EC loss between the studies that adopted a minimum ACD of 3.0 mm or smaller compared with studies adopting a minimum ACD of greater than 3.0 mm (Figure 4). This may be explained by the fact that the mean ACD is above 3.11 mm in all studies (ranging from 3.11 to 3.87 mm).

Secondary Surgical Intervention

The need for secondary surgical intervention after the iris-fixated pIOL implantation is summarized in Tables 11 and 12 as well as in Figure 6 and specified in more detail in Appendix 5 (see Supplemental Digital Content 1, available at http://links.lww.com/JRS/A5).

Table 11
Table 11:
Secondary surgical intervention in myopic eyes.
Table 12
Table 12:
Secondary surgical intervention in hyperopic eyes.
Figure 6
Figure 6:
Reasons for secondary surgical intervention (ACRS = additional corneal refractive surgery; IF-pIOL = iris-fixated phakic intraocular lens).

A total of 23 studies report on secondary surgical intervention in myopic eyes, with a total of 3636 myopic eyes. Secondary surgical intervention was needed in 0% to 27.1% of the myopic eyes. Four studies report on secondary surgical intervention in hyperopic eyes, with a total of 217 eyes. Secondary surgical intervention was needed in 2.2% to 46% of the hyperopic eyes.

Repositioning

Repositioning of the iris-fixated pIOL may be necessary due to inadequate surgical fixation or due to inadequate fixation after trauma. Overall, pIOL repositioning or re-enclavation was reported in a total of 59 myopic eyes, of which 23 were due to posttraumatic causes.3,5,12,13,15,16,22,27,31,32

IOL Exchange

Iris-fixated pIOL exchange was performed in a total of 20 myopic eyes and in 2 hyperopic eyes reported in 6 studies due to refractive undercorrection or overcorrection.3,12,22,27,30,31 In 4 eyes, the pIOL was exchanged because of a pupil diameter exceeding the optic diameter/glare or halo complaints.27,31

Correction of Residual Refractive Error

An undesirable amount of residual refractive error can be corrected by exchanging the iris-fixated pIOL either for an iris-fixated pIOL of different dioptric powers or for a different iris-fixated pIOL model. Another way of correcting residual refractive error is to combine the iris-fixated pIOL implantation with additional corneal refractive surgery, which was performed in 114 myopic eyes and 21 hyperopic eyes.3,23,31,32

IOL Explantation

The main reason for explantation of the iris-fixated pIOL in the myopic eye study was due to the formation of significant visual cataract.3,8,17,18,23,27,30,31 Patients were between 46 and 62 years at the time of cataract extraction with iris-fixated pIOL removal. Almost all cataracts described were of the nuclear sclerotic type.11,17,18,27,32 Cataract formation is overall described as having no direct causative relationship with the iris-fixated pIOL implantation. Only 1 study describes a case that can be attributed to the surgical procedure, acute glaucoma followed by crystalline lens opacification.22

Iris-fixated pIOL explantation due to excessive EC loss ranged from 0% to 0.9%.3,6,8,16,31 Explantation after traumatic causes was reported in 7 eyes.3,15,27 In 3 myopic eyes, the pIOL was explanted because of an inflammatory response.27

Iris-fixated pIOL explantation due to glare/halo complaints or a pupil diameter exceeding the optic diameter was described in 3 eyes.3,17,27 The need for retinal repair is reported to be in the range of 0% to 2.4%.15,16,27,32,33 The main reason for explantation in hyperopic eyes is the formation of posterior synechiae and pigment cell deposits.19,20

Other Complications

A concern with AC pIOLs is the development of secondary glaucoma due to pigment dispersion, pupillary block, or an uncontrollable inflammatory response. Pigment dispersion is likely to be caused by abnormal pressure on the iris.20,38 Baïkoff et al.20 describe that of a total of 273 implanted iris-fixated pIOLs (137 myopic and 136 hyperopic eyes), 9 eyes developed pigment dispersion, 8 (5.9%) of which were in hyperopic patients. Although ACs in all eyes were deep enough and irides that were considered too convex were excluded, they found a significant difference in crystalline lens anatomy between the hyperopic and myopic eyes. Saxena et al.19 report a percentage as high as 15% with pigment dispersion in hyperopic eyes.

To prevent pupillary block, an iridotomy or iridectomy is placed in eyes with iris-fixated pIOLs. There were cases of pupillary block reported in which no iridotomy or iridectomy was placed or the original iridotomy was closed.27 There was also 1 case of malignant glaucoma for which filtration surgery was needed.15 However, overall, increased intraocular pressure is uncommon in the long term.

Transient intraocular pressure elevation is mostly described as an early phenomenon arising from corticosteroid use in the early postoperative period. Optic phenomena such as glare and halo complaints can be related to surgical factors of poor centration or cases in which the pupil diameter exceeded the optic.3 Glare/halos were reported to be within a range of 0% to 22.2%. Of the highest percentage reported by Landesz et al.,11 only 2 of 8 patients were disturbed enough by the halos at night that they sometimes used pilocarpine. Moshirfar et al.22 and Titiyal et al.16 report 2.7% and 3.9% of glare/halo complaints at 2- and 4-year follow-up, respectively. Tahzib et al.23 scored optic phenomena with a valued questionnaire at 10-year follow-up and reported low scores. Optic phenomena seem to decrease over time and rarely require further action.5,7,16

DISCUSSION

The aim of this systematic review and meta-analysis was to gather all relevant data from the literature on the middle- and long-term effects after implantation of the convex-concave–shaped rigid iris-fixated pIOL (Artisan/Veriseye) for the correction of myopia and hyperopia. After a systematic search, 32 articles were selected and data were collected, reviewed, and summarized in pooled estimates.

Refractive Results

A fair to excellent refractive outcome and high stability of the SE over time has been demonstrated by the articles included in this review. Although a wide range of 55% to 98% of eyes is reported to have a deviation within 1.0 D from the targeted refraction, a clear majority of the studies report a mean MRSE within 1.0 D of emmetropia at the last follow-up, without any significant change in the SE over time. When interpreting the results on the deviation of the postoperative SE of targeted refraction, it is important to consider that pure predictability reflects the accuracy of the Van der Heijde formula combined with the surgically induced changes in refraction and is best determined in the period of 3 to 6 months after implantation.24 When describing long-term data on the SE within a certain range, we can only speak of refractive stability because refractive changes due to other reasons might have occurred over time (eg, cataract, progressive elongation of the axial length, and corneal changes).

Visual Outcome

Overall visual outcomes of the iris-fixated pIOL are encouraging, with stable safety indices of above 1.0 in myopic eyes up to 5 years after implantation. Thus, most eyes have a stable or a gain in CDVA. This outcome can be explained by the image magnification effect on the retina with a pIOL in place compared to refractive correction with spectacles, being partly due to the high optical and surface quality of the pIOL.39,40 Safety indices in hyperopic eyes are reported to be lower than those in myopic eyes. This can be explained by the retinal minification effect after pIOL implantation compared with spectacles. Most studies report less than 1% of the eyes losing 2 or more lines of CDVA. In eyes with a loss of 2 or more Snellen lines of CDVA, the authors claim that the main reasons are age-related cataract formation or the nature of myopic eye disease and not directly related to the implantation of the iris-fixated pIOL. In terms of efficacy, a significant gain in UDVA preimplantation vs postimplantation is reported by all authors, with all pooled estimates of the EI being above 0.8.

Corneal Endothelium

Accelerated EC loss has been, and still is, a great concern after any type of intraocular surgery, especially with the implantation of any type of AC IOL. Multiple pIOLs have been withdrawn from the market because of an unacceptable EC loss. The extent of EC change varies widely among the different studies involving the iris-fixated pIOL, ranging from a loss to a gain in ECs. The general trend, demonstrates a decrease in the EC density over time, with a comparable result between the myopic and hyperopic eyes. Pooled estimates reveal an annual decrease of 60 cells/mm2 in myopic eyes and 65.5 cells/mm2 in hyperopic eyes.

In clinical trials, corneal specular microscopy (CSM) is used to noninvasively study the EC layer of the cornea. The evaluation of the corneal ECs with CSM is susceptible to various errors. Internal CSM errors may arise from different sources, such as the accuracy of operator–software interaction, software imprecision, specular reflection limitations generating low-quality images, versatility for acquiring endothelial images, and sampling processes.41 It has also been shown that different brands of CSM cannot be interchanged reliably.42–44 Protocols to evaluate the corneal endothelium are not consistent among the studies included in this review and are mostly not described in detail. The long follow-up time generates additional errors in which changes, updates, or repairs of CSMs may have taken place, and new insights into how to perform and evaluate the corneal endothelium might lead to updates and adjustments in evaluation methods. Other reasons for a wide range of EC change may be due to surgical experience, patient selection criteria, characteristics of the patient population (eg, race and distribution of age in cohorts), the method of calculating and reporting EC change, a selection bias, the multicenter nature of the study, or reasons still unknown. There is no definite explanation for the wide range reported by the various authors. It may be multifactorial, and in this case, the extent to which each factor may contribute to the wide range in EC change also remains unknown. This fact emphasizes the need for regular follow-up visits and well-controlled prospective and comparative studies and studies with a long follow-up period. Guidelines on how to perform accurate analysis of the corneal endothelium and how to minimize the variability of CSM measurements should be encouraged.41,45

Cataract Formation

Most cataracts reported after iris-fixated pIOL implantation in myopic eyes were of the nuclear type and were the main reason for iris-fixated pIOL explantation. In hyperopic eyes implanted with iris-fixated pIOLs, cataract formation has not been described, but the study population is far smaller and the follow-up time far shorter compared with studies concerning myopic eyes. In their meta-analysis, Chen et al. report an incidence of cataract formation after Artisan/Verisyse pIOL implantation of 1.11% and 0.32% in myopic and hyperopic eyes, respectively, with half of the new onset of cataracts being of the nuclear sclerotic type.34 The mean time to cataract development was 37.65 months. Alio et al.35 describe the reasons for the explantation of various types of pIOLs in one of the largest consecutive case series. They report that almost half of the cases of iris-fixated pIOL explantation were due to nuclear cataract formation. The mean time between iris-fixated pIOL implantation and cataract development was 9.19 years, and the time between iris-fixated pIOL implantation and explantation was 9.55 years. Menezo et al.37 also report a case series of 7 out of 231 eyes (3%) that developed nuclear cataract after the implantation of an iris-fixated pIOL after a mean period of 4.7 years and, in which cataract extraction was performed, after a mean period of 11.4 years. Although 20% of the eyes were reported as being implanted with the older type of the biconcave Worst–Fechner iris-fixated pIOL, the type of cataract formation and time to cataract extraction is comparable to Alio et al. and the articles analyzed in this review.

Cataract formation is a potential complication of any surgical intraocular procedure, although a direct relationship between cataract formation and the iris-fixated pIOL has not been clearly shown. In cases in which iris-fixated pIOLs are implanted in highly myopic eyes, it is unclear whether cataract formation is due to the implantation procedure (complexity of the procedure and surgical experience) or related to the pIOL itself (material, metabolic effects, and intermittent touch), patient risk factors (trauma, medications, other diseases, and genetic predisposition), or high myopia. Data reported in long-term follow-up studies appear to support author claims that cataract development does appear to be directly related to iris-fixated pIOL implantation. Evidence in long-term, population-based follow-up studies has been provided to support the hypothesis that myopia and hyperopia itself may increase the risk of cataract development, especially of the nuclear type, compared with emmetropic eyes.46,47 However, more in-depth studies are needed to prove such statements and to clarify what factors contribute, and to what extent, to possibly earlier cataract development after pIOL implantation.

Glare/Halo

Optical phenomena, such as glare and halo may be caused by various factors such as a scotopic pupil size that exceeds the size of the lens optic, false light through a too large or not adequately located peripheral iridectomy or iridotomy, or a lens that is not stable and/or not adequately centered over the pupil entrance. The surgical procedure of enclavating an iris-fixated pIOL requires skill and practice and has a steep learning curve. A certain amount of enclavated iris tissue is required to ensure proper, stable, and well-centered enclavation. Greater surgical experience increases the ability to accurately enclavate the proper amount of the iris and center the iris-fixated pIOL over the pupil, which will lower the rate of re-enclavations.3,48 Although no standardized method is used to evaluate these subjective visual complaints in the various studies, optic phenomena seem to decrease over time and rarely require secondary surgical intervention.5,7,16

Other Complications

The factors mentioned as contributing to an increased risk of spontaneous subluxation include the quality and quantity of enclavated iris tissue at the initial implantation, the amount of iris manipulation during surgery, iris color, anatomy and architecture, and the amount of atrophy and depigmentation at the enclavation site.16,36,48 In addition to the articles studied in this review, Moran et al.36 have published a retrospective case series in which 2% of 609 eyes required re-enclavation with a follow-up of 11 years after Artisan or Artiflex implantation, which globally seems in line with the articles included in this review.

Reported rates of the need for retinal repair are low, ranging between 0% and 1.3%. However, there is no consistent protocol among the studies reviewed concerning prophylactic treatment of the retina; in one study, prophylactic panretinal laser photocoagulation was performed in all treated eyes.15 A higher risk for retinal detachment after pIOL implantation has been associated with an axial length of greater than 30 mm.35,49 In comparison with refractive clear lens exchange (RCLE), an alternative option to correct high refractive errors, Nanavaty and Daya50 state that pIOL implantation for the correction of myopic refractive errors may be a safer option than RCLE because retinal detachment in myopic eyes is a concern after RCLE, with incidences reported up to 8%.

Other complications, such as secondary glaucoma or other retinal problems, are rarely reported in myopic eyes. In hyperopic eyes though, severe pigment dispersion seems to present a problem, with an incidence rate of up to 15%.19 Moreover, the main reason for iris-fixated pIOL explantation in hyperopic eyes is the formation of pigment deposits and posterior synechiae formation. In a short-term study on iris-fixated pIOL implantation in primary and secondary hyperopia, Alio et al.38 also reported that 5% of eyes developed posterior synechiae. It is believed that a convex-shaped iris increases the incidence of pigment dispersion.20,38 To decrease the risk Baïkoff et al.20 suggested adding the objective measurement of a crystalline lens rise to the safety criteria, instead of using the subjective observation of a convex iris configuration. Prospective or comparative studies to verify a reduction in the incidence of severe pigment dispersion in hyperopic eyes when considering the crystalline lens rise are unfortunately not available.

In conclusion, most articles in the literature present the results on myopic eyes with a medium-term follow-up of 2 to 4 years. Only a few studies present the results from a follow-up of 7 years or longer.

Main findings of our meta-analysis are:

  1. Visual and refractive results after the implantation of an iris-fixated pIOL for the correction of myopia are positive.
  2. The complication rate is low. Age-related cataract is the main reason for iris-fixated pIOL explantation. Endothelial cell loss seems acceptable, or perhaps better said incalculable, although the range of EC change is too wide to draw firm conclusions.
  3. Great care should be taken when considering implanting an iris-fixated pIOL in hyperopic eyes because complication rates, particularly pigment dispersion, might be higher than those in myopic eyes.
  4. More well-designed long-term studies are needed, especially in hyperopic eyes.

To provide more evidence for the long-term safety of the iris-fixated pIOL and other IOLs, and to enable proper comparison of different pIOLs and other methods to correct refractive errors, we advocate for standardized reporting methods for refractive surgery data. Initiatives proposed by journal authors and editors to achieve uniformity should be supported.26,51,52

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