Iris-fixated phakic intraocular lenses (pIOLs) are available for a wide range of refractive errors and in two diameters.1 The Artisan and Artiflex pIOLs (also known as Verisyse and Veriflex, respectively, in the United States; OPHTEC BV, Groningen, The Netherlands) are primarily used for correction of refractive errors in patients who are not suitable candidates for laser refractive surgeries. However, other interesting applications such as improving visual acuity in adult amblyopic eyes2 and keratoconus3 have been reported.
As an intraocular implant, safety features of pIOLs have always been a topic of interest. Although primary short-term trials did not demonstrate significant endothelial cell loss (SECL),4,5 later studies found long-term reduction in endothelial cell counts.6–12 The reduction was reported to be as high as 11.3%,12 14.0%,6 and 15.1%13 after a 5-year follow-up period.
Preoperative endothelial cell density (ECD) and anterior chamber depth (ACD) are two primary predictive factors of long-term endothelial cell safety.1 For this reason, a reasonable reservoir of endothelial cells is needed before surgery. A minimum preoperative ECD of 2,800 cells/mm2 for patients younger than 25 years, 2,650 cells/mm2 for age 26 to 30 years, 2,400 cells/mm2 for age 31 to 35 years, 2,200 cells/mm2 for age 36 to 45 years, and 2,000 cells/mm2 for those older than 45 years is recommended by the manufacturer.14 With regard to the ACD, although a minimum ACD of 3.20 mm was recommended by the manufacturer,14,15 values of 2.6 to 3.20 mm have been used by most studies as the cut-off point for implanting an iris-fixated pIOL.1,3,6,8,9,11,13,16 For investigators and clinicians interested in designing a new study or implanting iris-fixated pIOLs, the controversy between the recommendations and inclusion criteria of the studies is confusing. Furthermore, concern rises when patients with an ACD even greater than 3.20 mm experience notable long-term ECL.6,7,12 These observations suggest that recommended safe ACD for pIOL implantation should be reevaluated.
The purpose of this study was to determine any correlation between ACD and long-term change of ECD in patients who underwent pIOL implantation. We also looked for an optimal cut-off value for ACD.
Patients and Methods
This study was performed in compliance with the principles of the Declaration of Helsinki and approved by the Magrabi Hospital Institutional Review Board, Jeddah, Saudi Arabia. Potential participants were retrospectively selected from patients who underwent iris-fixated pIOL implantation for correcting myopia and/or astigmatism in Magrabi Eye Hospital between February 2001 and April 2007. Of the patients, all of those who had follow-up between February 2012 and July 2018 and had completed at least 9 years of follow-up were evaluated. Inclusion and exclusion criteria at the time of preoperative evaluation are tabulated in Table 1. Patients who experienced any ocular surgery, eye trauma, or chronic ocular conditions (eg, glaucoma or chronic uveitis) after pIOL implantation were excluded. Information including uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent (MRSE), ACD (measured from corneal epithelium to anterior pole of crystalline lens), aqueous depth (AQD, measured from corneal endothelium to anterior pole of crystalline lens), central corneal ECD, and pachymetry were recorded from the preoperative evaluation and the last follow-up visit. ECD was measured with an automated non-contact specular microscope (Tomey EM-3000; Tomey Corporation, Nagoya, Japan) preoperatively and the Nidek CEM-530 (Nidek Corporation, Tokyo, Japan) on the last follow-up visit. Three consecutive central automated measurements were obtained and the one with the best quality was used. The Orbscan II (Bausch & Lomb, Rochester, NY) or IOLMaster 500 (Carl Zeiss AG, Oberkochen, Germany) was used for the measurement of ACD and AQD on the first visit, which provides significant accuracy and agreement.17–19
Inclusion and Exclusion Criteria
Patients underwent implantation with the Artisan Myopia (model 204 or 206 with 6- and 5-mm optic diameter, respectively; overall length 8.5 mm), Artisan Toric (5-mm optic diameter, overall length 8.5 mm), or Artiflex (foldable, 6-mm optic diameter, overall length 8.5 mm) IOL, all manufactured by OPHTEC BV. Model 206 was used for lens powers up to −15.00 diopters (D) and model 206 for lens powers between −15.00 and −23.50 D. The pIOLs were positioned in the anterior chamber of the eyes and fixed to the mid-periphery of the iris. All procedures were performed by the same experienced surgeon (AME), using the same technique described previously.20
For better identification of risk factors associated with the long-term endothelial cell changes, SECL on the last follow-up visit was defined as loss of more than 30% of endothelial cells compared to the baseline and/or ECD of 1,500 cells/mm2 or less and/or corneal edema.
The primary outcome measure was to determine the long-term correlation between ECD change and preoperative ACD. Secondary outcome measures were to identify potential risk factors for SECL and to find the optimal cut-off value for preoperative ACD in patients who underwent pIOL implantation.
Excel software (Microsoft Corporation, Redmond, WA) was used for data collection and performing descriptive analysis. SPSS for Windows software (version 17; SPSS, Inc., Chicago, IL) was used for data analysis. All continuous variables are reported as mean ± standard deviation (SD) and range. Snellen visual acuity was converted to logMAR units for analysis. A predicted physiologic decline of 0.6% per year was applied to the last follow-up ECD values.21,22 All of the comparisons were performed after this adjustment. Due to the severe corneal edema/decompensation, obtaining the ECD on the last follow-up visit was not possible in 10 eyes. Excluding those eyes from the study would induce a significant bias to our results. Previous studies revealed that significant corneal edema/decompensation develops when the density of central corneal endothelial cells drops below 300 to 700 cells/mm2.23–25 Accordingly, we considered an endothelial cell count at last follow-up visit of 500 cells/mm2 for those eyes.
The paired t test was used for comparison of continuous variables preoperatively and on the last follow-up visit. The one-way analysis of variance test was used to compare three different groups of ACD. A post-hoc test (Tukey test) was used to confirm whether the differences between groups were significant. The Pearson correlation coefficient (r) was applied to determine the correlation between percentage of ECL and preoperative ACD and AQD values. Odds ratios (ORs) and 95% confidence intervals (CIs) were obtained from multiple logistic regression models to identify risk factors for SECL. Receiver operating characteristic (ROC) curve analysis was used to obtain optimum cut-off points for ACD and AQD. A P value of less than .05 was considered statistically significant.
Ninety eyes of 57 patients were enrolled. Preoperative characteristics of the eyes are summarized in Table 2. Thirty-one (54%) patients were women and 26 (46%) were men. The pIOLs were placed bilaterally in 33 (58%) patients and unilaterally in 24 (42%) patients. The mean follow-up time was 11.7 ± 2.0 years (range: 9.1 to 17.3 years). Three types of pIOLs were implanted: Artisan Myopia in 69 (77%) eyes, Artisan Toric in 7 (8%) eyes, and Artiflex in 14 (15%) eyes. Sixty-six (73%) lenses had an optic diameter of 6 mm and 24 (27%) had an optic diameter of 5 mm.
On the last visit, the mean sphere was −0.54 ± 1.34 D (range: −5.00 to +1.50 D) and the mean cylinder was −1.40 ± 0.89 D (range: −4.00 to 0.00 D). CDVA and UDVA were 20/29 ± 20/33 (range: 20/400 to 20/16) and 20/57 ± 20/60 (range: 20/2000 to 20/16), respectively. More information is displayed in Figure 1.
(A) Postoperative distance visual acuity. (B) Difference between uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) (Snellen lines). (C) Spherical equivalent refractive accuracy. (D) Refractive cylinder. D = diopters
The mean ECD on the last visit was 1,751 ± 730 cells/mm2 (range: 500 to 3,307 cells/mm2). Compared to the baseline data, the mean ECD change was −894 ± 732 cells/mm2 (range: −2,281 to 389 cells/mm2). The mean percentage of this change was −26.7% ± 27.6% (range: −75.1% to 16.8%) (P < .001).
Of the 90 eyes, 32 (36%) eyes reached SECL criteria. The mean preoperative ACD was 3.14 ± 0.13 mm (range: 3.00 to 3.49 mm) in eyes with SECL and 3.62 ± 0.28 mm (range: 3.00 to 4.20 mm) in those without SECL (P < .001). The mean preoperative AQD was 2.60 ± 0.13 mm (range: 2.40 to 2.90 mm) in the eyes that met SECL criteria and 3.10 ± 0.27 mm (range: 2.50 to 3.60 mm) in those that did not (P < .001). The differences between age, IOL type, IOL diameter, MRSE, and preoperative pachymetry were not statistically significant between eyes that experienced SECL and those that did not (P > .05).
To better determine the association between preoperative ACD values and the long-term ECD change, eyes were divided into three groups based on the preoperative ACD values: 3.20 mm or less, 3.21 to 3.49 mm, and 3.50 mm or greater (Figure 2). The mean ECD change from baseline was −53.5% ± 19.1% (range: −75.1% to −5.2%) in the 3.20 mm or less group, −26.0% ± 26.6% (range: −74.1% to 0.9%) in the 3.21 to 3.49 mm group, and −5.2% ± 8.7% (range: −21.3% to 16.8%) in the 3.50 mm or greater group. The differences between groups were statistically significant (P < .001). SECL was present in none of the eyes in the 3.50 mm or greater group, 29% (6 of 21) in the 3.21 to 3.49 mm group, and 84% (26 of 31) in the 3.20 mm or less group. The differences between the groups in terms of reaching SECL criteria were also significant on post-hoc test (P < .001). Of the 10 eyes with corneal edema, 6 had an ACD of 3.20 mm or greater and the remaining 4 belonged to the 3.21 to 3.49 mm group. Further characteristics of the three groups are described in Table 3.
Mean central corneal endothelial cell density preoperatively and on the last visit based on the anterior chamber depth.
Characteristics of the Eyes on the Last Follow-up Visit Based on the Preoperative ACD
Multivariate analysis was performed to detect major risk factors associated with SECL. Whereas the definition of ACD includes the value of AQD, we performed two separate multivariable analyses and every time we considered either ACD or AQD in the analysis. We included potential risk factors such as MRSE, IOL diameter (5 or 6 mm), IOL type (Artisan Myopia, Artisan Toric, or Artiflex), preoperative pachymetry, and age (as a continuous variable and also when considered as younger or older than 30 years) in both analyses that were performed with ACD and AQD. Shallower preoperative ACD (OR [95% CI] = 12.50 [3.83 to 41.75]; P < .001) and shallower preoperative AQD (OR [95% CI] = 7.87 [1.83 to 34.48]; P < .006] were significant risk factors for SECL, separately. For each 100-µm decrease in ACD and AQD, the odds of SECL occurring increases 12.50 and 7.87 times, respectively. A strong negative correlation was found between preoperative ACD value and percentage of ECL (r = −0.70; P < .001). The negative correlation between preoperative AQD value and percentage of ECL was also strong (r = −0.65; P < .001). Eyes with shallower ACD or AQD experienced more ECL (Figure 3). ROC curve analysis was performed to obtain the optimal ACD cut-off value to avoid SECL. ROC curve revealed that at a cut-off value of 3.35 mm, sensitivity was 83% and specificity was 91%. At a cut-off value 3.50 mm, sensitivity was 62% and specificity was 100%. At a cut-off value of 3.15 mm, sensitivity and specificity were 98% and 50%, respectively. We also performed ROC curve analysis to find optimal numbers for the preoperative AQD value. Sensitivity was 88% and specificity was 81% for 2.75 mm, and sensitivity was 79% and specificity was 85% for 2.81 mm.
Correlation between preoperative anterior chamber depth (ACD) and endothelial cell density (ECD) change. A strong negative correlation is seen between preoperative ACD and percentage of ECD change over 11.8 ± 2.0 years (range: 9.1 to 17.3 years) (r = −0.70; P < .001).
Some of the patients experienced adverse effects. The pIOL explantation was performed in 30 (33%) eyes. The pIOLs were removed from 8 (9%) eyes due to the SECL (ECD of 1,500 cells/mm2 or less without clinical edema) after 10.3 ± 1.1 years (range: 9.1 ± 11.6 years) of implantation, from 6 (7%) eyes because of development of senile cataract without SECL after 11.6 ± 1.7 years (range: 9.5 ± 13.5 years), from 6 (7%) eyes due to development of cataract and SECL (ECD of 1,500 cells/mm2 or less without clinical edema) after 11.6 ± 2.5 years (range: 9.5 ± 16.3 years), and from 10 (11%) eyes by reason of SECL (corneal edema) after 12.1 ± 2.0 years (range: 9.3 to 15.1 years). For the last 10 eyes, Descemet's stripping automated endothelial keratoplasty (DSAEK) was performed. The mean follow-up time after DSAEK was 1.6 ± 1.4 years (range: 0.2 to 5.0 years) and the mean ECD on the last visit after DSAEK was 1,842 ± 909 cells/mm2 (range: 954 to 2,964 cells/mm2) (Figure 4).
(A) Right eye of a 52-year-old patient with Artiflex (OPHTEC BV, Groningen, The Netherlands) implantation who was lost to follow-up and presented 12 years after surgery with gradually decreased vision (UDVA: 20/100). Preoperative data (before phakic intraocular lens [pIOL] implantation): UDVA: counting fingers; manifest refraction: − 6.25 −0.25 × 10; CDVA: 20/20; ACD: 3.20 mm; AQD: 2.60 mm; ECD: 2,686 cells/mm2. Post pIOL implantation data: UDVA: 20/22; manifest refraction: 0.00 −0.50 × 055; CDVA: 20/20. (B) Same eye, 5 months after Artiflex removal combined with phacoemulsification, posterior chamber IOL implantation, and Descemet stripping automated endothelial keratoplasty (DSAEK). UDVA: 20/100; manifest refraction: −1.50 −1.00 × 45; CDVA: 20/25; ECD: 1,952 cells/mm2. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; ACD = anterior chamber depth; ECD = endothelial cell density; AQD = aqueous depth
In the current study, shallower ACD and AQD were strongly correlated with greater ECL in patients with implanted pIOLs. Our results demonstrated that shallower ACD and AQD are significant risk factors for encountering corneal endothelial cell loss after pIOL implantation. We also proposed cut-off points for preoperative ACD and AQD to reduce facing significant loss of corneal endothelial cells in the long term.
Endothelial safety of pIOLs has been controversial. In 2000, the European Multi-Center Study sponsored by the manufacturer (OPHTEC BV) reported that the primary decline in endothelial cells would be stabilized to the normal physiologic level 3 years after surgery.5 The U.S. Food and Drug Administration OPHTEC Study in 2004 did not report SECL after a 2-year follow-up.4 However, the results from subsequent long-term studies changed this perspective. Shajari et al.11 implanted pIOLs and reported a mean ECL of 11% ± 12% (range: 38% to 11%) after the fourth year. Saxena et al.8 followed up patients after pIOL implantation for 7 years and reported a significant correlation between shallower anterior chamber and ECL. The correlation in their study became evident after 3 years of follow-up and remained significant up to 7 years. Recently, Jonker et al.7 reported a linear decline in ECD with total loss of 16.6% in the Artisan Myopia group and 21.4% in the Artisan Toric group from 6 months to 10 years of implantation. We found a significant ECD change of −26.7% ± 27.6% (range: −75.1% to 16.8%) over the mean follow-up time of 11.7 ± 2.0 years. Other studies reported ECL of 11.3%,12 14.0%,6 and 15.1%13 after a 5-year follow-up. Although linear decrease in ECD has been reported after pIOL implantation,7 the difference in reported numbers can be explained by the longer follow-up time in our patients. Other possible explanations include different baseline ECD, different baseline ACD, using various machines for measurements, adjusting or not adjusting physiologic loss in the reports, and different surgical methods.
Bouheraoua et al.13 introduced a model to predict annual ECL after pIOL implantation. The pIOLs were implanted in eyes with ACD of 3.0 mm or greater and patients were followed up for 5 years. Adding information from previous studies to their model, the authors proposed the mean yearly loss of 3.9% in the first year and 1.7% per year after the first year. The mean annual ECL in our patients was 2.28%, which was close to the model introduced by Bouheraoua et al. However, our study emphasized that the annual loss was strongly influenced by the preoperative ACD when it was 4.4% in eyes with an ACD of 3.20 mm or less and 0.4% in eyes with an ACD of 3.50 mm or greater (Table 3).
Shallower ACD and AQD were significant risk factors for SECL in our study. Primary ECD also plays a major part in long-term safety. When the pIOL was approved by the U.S. Food and Drug Administration in 2004,15 a minimum ECD of 3,550 cells/mm2 was recommended for age 21 to 25 years, 3,175 cells/mm2 for age 26 to 30 years, and 2,225 cells/mm2 for age 41 to 45 years. To the best of our knowledge, none of the available clinical studies followed those values. The reason that clinicians do not follow the age-adjusted recommendations is unclear to us. One possibility is that the recommended numbers were set too high and seemed sophisticated. The safety ECD value used by most of the studies was 2,000 to 2,300 cells/mm2 for all ages.1,5,6,8–11,13,26,27 In the latest recommendation on the manufacturer's web site (the IRIS brochure),14 different numbers have been proposed. Those numbers included a minimum preoperative ECD of 2,800 cells/mm2 for patients younger than 25 years, 2,650 cells/mm2 for 26 to 30 years, 2,400 cells/mm2 for 31 to 35 years, 2,200 cells/mm2 for 36 to 45 years, and 2,000 cells/mm2 for older than 45 years. Even considering these lower numbers, only one study followed the recommendations.7 This fact enhances the importance of considering greater ACD values to compensate for lower ECD threshold used by many clinicians.
The other fact that should be taken into account when considering a safe value is that the ACD is not constant. Sekundo et al.28 reported that the peripheral ACD decreases up to 17% in some eyes during accommodation. In addition, Schöpfer et al.29 demonstrated a significant ACD change in eyes with pIOL implantation depending on the head position. In their study, ACD became 78 µm shallower during forward movement of the head. Furthermore, ACD begins to reduce with age.30,31 Although the minimum ACD of 3.0 mm for Artisan and 3.20 mm for Artiflex is suggested by the manufacturer,14 our experience showed that the ACD of 3.0 mm or greater used in our study is not a safe value for pIOL implantation. Our ROC curve analysis proposed an ACD value of 3.35 mm to be safe with reasonable sensitivity and specificity. We believe that an ACD of 3.35 mm or greater is a safe value, whereas a minimum ECD of 2,200 cells/mm2 is considered for inclusion criteria.
AQD is another value that can be used for safety purposes of pIOL implantation. It can be precisely measured by current non-contact devices such as the Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany), IOLMaster (Carl Zeiss AG, Oberkochen, Germany), and Galilei (Ziemer Ophthalmics, Port, Switzerland). Unlike the concept of ACD, which includes the value of corneal thickness, AQD is an internal measurement and represents the actual space for the pIOL. Some studies used AQD as opposed to ACD for the inclusion of the patients.2,7,32,33 To the best of our knowledge, no other study suggested the optimal AQD for iris-fixated pIOL implantation. Our results revealed that with a preoperative AQD of 2.75 mm, sensitivity and specificity for detecting SECL were 88% and 81%, respectively, which makes this number a remarkable cut-off point.
Our study had some limitations. Because of the nature of this study, it suffered from all limitations of a retrospective non-randomized study. The long follow-up period (range: 9.1 to 17.3 years) made us replace some of our devices because of the improvement in technology and half-life of the machines. For this reason, we needed to use two different specular microscopes over the course of the study. However, there is strong agreement between the two specular microscopes that we used.34
We demonstrated that there is significant negative correlation between ACD and ECL in patients with pIOLs. Eyes with shallower ACD and AQD are at greater risk for SECL. We believe that the current recommendation for the safe value of ACD should be reconsidered. Based on the results of this study, when the minimum ECD of 2,200 cells/mm2 is used, we suggest an ACD of 3.35 mm or greater for implanting iris-fixated pIOLs. Besides ACD, for the first time, we proposed an AQD of 2.75 mm as a safe cut-off value.
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- Jonker SMR, Berendschot TTJM, Ronden AE, Saelens IEY, Bauer NJC, Nuijts RMMA. Long-term endothelial cell loss in patients with Artisan myopia and Artisan toric phakic intraocular lenses: 5- and 10-year results. Ophthalmology. 2018;125:486–494. doi:10.1016/j.ophtha.2017.08.011 [CrossRef]
- Saxena R, Boekhoorn SS, Mulder PGH, Noordzij B, van Rij G, Luyten GPM. Long-term follow-up of endothelial cell change after Artisan phakic intraocular lens implantation. Ophthalmology. 2008;115:608–613. doi:10.1016/j.ophtha.2007.05.036 [CrossRef]
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- Artisan® Phakic IOL Facts You Need to Know About Implantation of the Artisan® Phakic IOL (−5 TO −20 D) for the correction of myopia (nearsightedness). Patient information brochure. 2004. https://www.accessdata.fda.gov/cdrh_docs/pdf3/P030028d.pdf. Accessed March 16, 2018.
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Inclusion and Exclusion Criteria
|Myopia between −5.00 and −20.00 D||History of additional eye surgery|
|Central ACD of ⩾ 3 mm||History of eye trauma|
|Age ⩾ 18 years||Cataract|
|Documented stable refraction for 1 year||Preexisting macular or retinal disease|
|Astigmatism up to 6.00 D||Chronic eye conditions such as glaucoma and uveitis|
|CDVA ⩾ 20/40|
|Scotopic pupil size > 5 or 6 mm based on the lens model|
|Ability to consent to the procedure in writing|
|Characteristic||Mean ± SD||Range|
|Age (y)||30.3 ± 8.3||18.0 to 53.0|
|Refraction sphere (D)||−10.15 ± 5.69||−23.00 to 0.00|
|Refraction cylinder (D)||−1.59 ± 1.15||−6.00 to 0.00|
|MRSE (D)||−10.95 ± 5.73||−24.50 to −2.00|
|ACD (mm)||3.45 ± 0.33||3.00 to 4.20|
|Pachymetry (mm)||538 ± 37||460 to 615|
|AQD (mm)||2.91 ± 0.33||2.40 to 3.60|
|IOL power sphere (D)||−11.33 ± 5.70||−23.00 to 0.00|
|IOL power cylinder (D)||−4.21 ± 1.18||−6.00 to −3.00|
|CDVA||20/35 ± 20/39||20/40 to 20/20|
|Central ECD (cells/mm2)||2,645 ± 200||2,212 to 3,533|
Characteristics of the Eyes on the Last Follow-up Visit Based on the Preoperative ACD
|Preoperative ACD (mm)||SECL||Follow-up Time (Mean ± SD) (y)||Mean ECD Change/Year||Cumulative Mean ECD Change (Mean ± SD)a||95% CI for Cumulative ECD|
|⩽ 3.20||26 (84%)||5 (16%)||12.1 ± 2.2 (range: 9.2 to 16.5)||−4.4%||−53.5% ± 19.1% (range: −75.5% to −5.2%)||−60.5% to −46.5%|
|3.21 to 3.49||6 (29%)||15 (71%)||11.3 ± 1.8 (range: 9.2 to 15.9)||−2.3%||−26.0% ± 26.6% (range: −74.1% to 0.9%)||−38.1% to −13.8%|
|⩾ 3.50||0 (0%)||38 (100%)||11.7 ± 2.0 (range: 9.1 to 17.3)||−0.4%||−5.2% ± 8.7% (range: −21.3% to 16.8%)||−8.1% to −2.3%|
|All eyes||32 (36%)||58 (64%)||11.7 ± 2.0 (range: 9.1 to 17.3)||−2.28%||−26.7% ± 27.6% (range: −75.1% to 16.8%)||−32.5% to −20.9%|