Journal of Refractive Surgery

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The Kelman Duet Phakic Intraocular Lens: 1-year Results

Jorge L Alió, MD, PhD; David Piñero, OD; Gonzalo Bernabeu, MD; Ahmed Galal, MD, PhD; José Manuel Vargas, MD; Mahmoud M Ismail, MD, PhD

Abstract

ABSTRACT

PURPOSE: To evaluate the efficacy and safety of the Kelman Duet phakic intraocular lens (PIOL) for correction of moderate and high myopia.

METHODS: Kelman Duet PIOLs were implanted in 169 eyes of 110 patients with moderate or high myopia. In all cases, implantation of the lens was feasible through an incision of less than 2.5 mm without complications. Uncorrected visual acuity (UCVA), manifest refraction, best spectacle-corrected visual acuity (BSCVA), intraocular pressure, central corneal endothelial change, and complications were recorded preoperatively and during 12 months of follow-up.

RESULTS: Following PIOL implantation, 23 (13.61%) eyes required LASIK retreatment for the correction of residual astigmatic refractive error and were excluded from the refractive analysis. Best spectacle-corrected visual acuity remained the same or improved in 95.04% of eyes, 81.30% of eyes (100) were within ±1.00 diopter (D) of emmetropia, and 57.72% (71) were within ±0.50 D. Intraocular pressure increased slightly in the first 4 weeks postoperatively but stabilized to the preoperative level by 3 months. Mean endothelial cell ioss at 12 months was 5.43%. Oval pupils developed in 10.1% of eyes. Haptic exchange or reposition was performed in 7.76% of cases.

CONCLUSIONS: The Kelman Duet PIOL was safe and effective for the correction of moderate to high myopia in this study with 1-year follow-up and offered the advantage of using a 2. 5-mm or less incision width. Accurate haptic sizing remains a challenge and haptic exchange to correct haptic size mismatching is possible. [J Refract Surg. 2007;23:868-879.]

Abstract

ABSTRACT

PURPOSE: To evaluate the efficacy and safety of the Kelman Duet phakic intraocular lens (PIOL) for correction of moderate and high myopia.

METHODS: Kelman Duet PIOLs were implanted in 169 eyes of 110 patients with moderate or high myopia. In all cases, implantation of the lens was feasible through an incision of less than 2.5 mm without complications. Uncorrected visual acuity (UCVA), manifest refraction, best spectacle-corrected visual acuity (BSCVA), intraocular pressure, central corneal endothelial change, and complications were recorded preoperatively and during 12 months of follow-up.

RESULTS: Following PIOL implantation, 23 (13.61%) eyes required LASIK retreatment for the correction of residual astigmatic refractive error and were excluded from the refractive analysis. Best spectacle-corrected visual acuity remained the same or improved in 95.04% of eyes, 81.30% of eyes (100) were within ±1.00 diopter (D) of emmetropia, and 57.72% (71) were within ±0.50 D. Intraocular pressure increased slightly in the first 4 weeks postoperatively but stabilized to the preoperative level by 3 months. Mean endothelial cell ioss at 12 months was 5.43%. Oval pupils developed in 10.1% of eyes. Haptic exchange or reposition was performed in 7.76% of cases.

CONCLUSIONS: The Kelman Duet PIOL was safe and effective for the correction of moderate to high myopia in this study with 1-year follow-up and offered the advantage of using a 2. 5-mm or less incision width. Accurate haptic sizing remains a challenge and haptic exchange to correct haptic size mismatching is possible. [J Refract Surg. 2007;23:868-879.]

Laser in situ keratomileusis (LASIK) and photorefractive keratectomy have become common surgical options for the correction of myopia. However, in cases of high myopia, these keratorefractive techniques are associated with an increased risk of corneal ectasia1"3 and a significant loss of visual quality.4"7 For these reasons, phakic intraocular lenses (PIOLs) recently have increased in popularity.8 Several reports have confirmed the efficacy and predictability of PIOLs in correcting high myopia,9"16 but historically, concerns have existed regarding long-term safety. Some studies on PIOLs have documented the potential effect of first-generation PIOLs on the corneal endothelium as well as a potential for developing intraocular problems.12141517"20 However, modern designs of PIOLs have been shown not to damage anterior segment structures, especially the corneal endothelium, and have maintained intraocular pressure (IOP), while also offering optical advantages over other refractive procedures.9,11,16,21,22

Phakic intraocular lenses are a promising alternative for high refractive error correction. Phakic intraocular lens implantation offers well-defined advantages as a refractive surgical technique because of its simplicity, potential reversibility, and precision, as well as the high degree of achieved optical quality.23 24 They maintain the original prolate shape of the cornea and do not alter the corneal geometry, in contrast to keratorefractive procedures. Corneal procedures are subject to wound healing and biomechanics, both of which influence the precision and stability of the results. Additionally, as keratorefractive procedures, PIOLs preserve accommodation (the natural lens is not extracted, which provides the accommodative function) and therefore are suitable for younger patients, in contrast with crystalline lens surgery.

Figure 1. The optic and haptic of the Kelman Duet lens.Figure 2. Appearance of a Kelman Duet lens implanted correctly.

Figure 1. The optic and haptic of the Kelman Duet lens.

Figure 2. Appearance of a Kelman Duet lens implanted correctly.

The development of modern microsurgery and viscoelastics, in conjunction with the improvement in surgical knowledge and skills regarding the use of intraocular lenses made of flexible materials, has contributed to the increasing popularity and use of PIOLs. Modern PIOLs also have the benefit of the latest technological developments in lens design and manufacturing. Another advantage of these lenses is their potential for safe explantation, enabling refractive surgeons to perform other intraocular procedures such as cataract surgery,25 with similar results to those obtained in unoperated eyes.

Phakic intraocular lenses can be grouped into three basic types: anterior chamber angle-fixated, anterior chamber iris-fixated, and posterior chamber lenses. All three types of PIOLs have been modified since 1989. The first-generation of the angle-supported PIOL was associated with several complications, especially high endothelial cell loss and pupil ovalization.19 Modern designs such as the recent foldable models have minimized these problems. Angle-supported PIOLs are implanted using a simple surgical technique and produce good refractive results, as previous studies have reported.10,16,21,23,24

The Kelman Duet Implant (Tekia Ine, Irvine, Calif) is a two-part, angle-supported PIOL that is implantable through a small incision (Fig 1). The main advantage of this specific kind of lens is the exchangeability of both the lens haptic and optic (Fig 2). It is known that the human myopic eye may experience optical and refractive changes such as progressive myopia, presbyopia, or changes in lens asphericity throughout the life span. Exchangeability of the optic is an option that allows the implant to be adapted for these future refractive changes. This fact is one of the most important improvements in design provided by the Kelman Duet lens. Another positive advantage of this lens is the possibility of selecting the appropriate size of the haptic depending on the anatomic characteristics of the anterior segment. This enables a specific complication of angle-supported PIOLs (ie, pupil ovalization due to inadequate selection of the size of the lens) to be solved.

In a previous report,26 we published the promising results of a pilot study on the Kelman Duet lens, with separate implantation of the haptic and optic through a sub-2.5-mm incision (incision width less than 2.5 mm). This multicenter and collaborative study evaluates the 1-year clinical and refractive results of the Kelman Duet PIOL for the correction of high myopia.

PATIENTS AND METHODS

IMPLANT DESCRIPTION

The Kelman Duet lens is a two-part, angle-supported PIOL consisting of the haptic and optic (see Fig 1). Both parts are independent and implantable through a sub2. 5-mm incision. The polymethylmethacrylate haptic has three points of support and provides smooth contact with the angle structures. Different sizes are available (12.0, 12.5, and 13.0 mm) and angulations vary from 11.1? to 9.6? depending on the total size of the haptic. The optic used in this clinical study is made of silicon and has a total diameter of 6 mm. It has two tabs that enable perfect fitting to the haptic frame. The optic is available in 1 -diopter (D) increments in optic power. The periphery area of the optic has a glare-preventing shield to avoid light reflexes in dim light conditions.

Study Design and Population

This prospective, consecutive, nonrandomized, collaborative study was started in September 2001 and was preceded by a successful pilot study reported previously.26 The coordination center of this international multicenter study was the Vis sum/Insti tuto Oftalmol?gico de Alicante, Alicante, Spain (110 implantations). The other two participating centers were the Magrabi Eye Hospital, Cairo, Egypt (9 implantations) and CEOVAL, Valencia, Venezuela (50 implantations). Three surgeons (J.L.A., J.M.V., M.M.I.) from the different centers performed Kelman Duet implantation using the same protocol with clinical monitoring during the first cases. This initial monitoring was performed by one of the surgeons at the coordinating center (J.L.A.).

During the study period, 169 eyes of 110 patients were implanted with the Kelman Duet PIOL, with minimum 12-month follow-up. Patient age ranged from 18 to 45 years. Mean preoperative spherical equivalent refraction was -14.26?4.54 D (range: -8.00 to -26.00 D). In all cases, the target postoperative refraction was emmetropia. Preoperative best spectacle-corrected visual acuity (BSCVA) was 0.68?0.25 (range: 0.10 to 1.20).

All patients were informed about the surgery, its risks and benefits, and provided written informed consent. Exclusion criteria were nonstable myopia (ie, any refractive change within the past 2 years), age <18 years for any degree of myopia, anterior chamber depth <3.0 mm (measured from the corneal endothelium), central corneal endothelial cell density of at least 2000 cells/mm2, BSCVA higher than 0.1, lens opacities, active corneal disease, glaucoma or ocular hypertension, history of uveitis, anterior or posterior synechiae, diabetic retinopathy, and a history of retinal detachment.

Pre- and postoperative measurements were performed at the different centers using the same protocols and the same instruments, except for corneal endothelial change. Because different protocols were used at each center to determine corneal endothelial changes, only data from the coordinating center were included in this analysis. Preoperative examination included uncorrected visual acuity (UCVA), manifest and cycloplegic refraction, BSCVA, slit-lamp microscopy, Goldmann tonometry, ultrasonic pachymetry (DHG500 US pachymeter; DHG Technology Ine, Exton, Pa), biometry (IOL Master, Carl Zeiss M?dit?e, Jena, Germany), white-to- white corneal diameter, corneal topography (CSO CM02; CSO, Firenze, Italy), corneal endothelial study, and fundus examination.

The size of the haptic, as recommended by the manufacturer, was selected using the following criteria: haptic diameter = white-to-white horizontal diameter + 0.5 mm.

SURGICAL TECHNIQUE

All surgeries were performed following the same surgical protocol under either topical or local anesthesia. One drop of 1% pilocarpine (Isoptocarpine; Alcon Cusi, Barcelona, Spain) was instilled into the eye 30 minutes before surgery. The theoretical details involved in the surgical use of this PIOL were reported previously in the pilot study26 and were not changed for the current study.

POSTOPERATIVE FOLLOW-UP

Patients were examined 1 day, 1 week, and 1, 3, 6, and 12 months postoperatively. On the first postoperative day, a detailed slit-lamp examination was performed to evaluate the lens position, pupil shape, and integrity of the anterior segment structures. At the remaining postoperative examinations, UCVA, manifest refraction, BSCVA, slit-lamp microscopy with special attention to pupil shape, IOP, fundus examination, and subjective patient satisfaction (eg, satisfaction with the surgery and night vision disturbances as halos or glare) were recorded.

Endothelial changes after implantation of the PIOL were studied using only the data from the coordinating center (110 eyes) to avoid technological bias in endothelial cell count analysis. Corneal endothelial study was performed at the central cornea by the same surgeon (G.B.A.) using the endothelial cell meter Konan SP5500 (Konan Camera Research Institute, Hyogo, Japan) preoperatively and at 3 and 12 months after surgery. To perform the endothelial cell study, a previously reported protocol was followed16,21,28 and was based on the analysis of 100 to 150 cells at the central cornea.

Table

TABLE 1Refractive Characteristics of 146 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*Figure 3. Change in postoperative spherical equivalent refraction (SE) after implantation with the Kelman Duet phakic intraocular lens. Error bars = + standard deviation.Figure 4. Intended spherical equivalent refraction (SE) versus achieved correction at 12 months after implantation with the Kelman Duet phakic intraocular lens.

TABLE 1

Refractive Characteristics of 146 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*

Figure 3. Change in postoperative spherical equivalent refraction (SE) after implantation with the Kelman Duet phakic intraocular lens. Error bars = + standard deviation.

Figure 4. Intended spherical equivalent refraction (SE) versus achieved correction at 12 months after implantation with the Kelman Duet phakic intraocular lens.

STATISTICAL ANALYSIS

Statistical analysis was performed using SPSS software version 10.1 (SPSS, Chicago, 111). Normality of the data analyzed was confirmed by the Kolmogorov-Smirnov test. When parametric analysis could be applied, Student t test for paired data was used for comparison, and differences were considered statistically significant when the probability value was <.05. However, when nonparametric tests were needed, the Wilcoxon rank sum test with the same level of significance was applied to assess the significance of differences between pre- and postoperative data.

Following the standard criteria, the efficacy index was calculated as the ratio of postoperative UCVA to preoperative BSCVA, and the safety index as the ratio of postoperative BSCVA to preoperative BSCVA.

RESULTS

A total of 169 eyes of 110 patients were implanted with the Kelman Duet lens. Twenty- three (13.61%) of these eyes were retreated with LASIK to eliminate residual cylindrical refractive error. These eyes were excluded from analysis of the final refractive outcomes because the optical properties of the cornea were modified during follow-up.

Figure 5. Predictability results at 12 months after implantation with the Kelman Duet phakic intraocular lens. All parameters were recorded for all eyes only at the preoperative visit. Data for some of the postoperative visits are missing because the patient did not follow up. Total number of eyes: preoperative = 146, 1 month = 146, 3 months = 128, 6 months = 131, and 12 months = 123.Figure 6. Cumulative postoperative uncorrected visual acuity (UCVA) at 12 months after implantation with the Kelman Duet phakic intraocular lens versus cumulative preoperative best spectacle-corrected visual acuity (BCVA).

Figure 5. Predictability results at 12 months after implantation with the Kelman Duet phakic intraocular lens. All parameters were recorded for all eyes only at the preoperative visit. Data for some of the postoperative visits are missing because the patient did not follow up. Total number of eyes: preoperative = 146, 1 month = 146, 3 months = 128, 6 months = 131, and 12 months = 123.

Figure 6. Cumulative postoperative uncorrected visual acuity (UCVA) at 12 months after implantation with the Kelman Duet phakic intraocular lens versus cumulative preoperative best spectacle-corrected visual acuity (BCVA).

REFRACTIVE OUTCOMES

Refractive results are shown in Table 1. Mean preoperative spherical equivalent refraction was ? 15.01?4.53 D (range: ?8.75 to ?26.00 D). Mean postoperative spherical equivalent refraction was ? 0.58?0.86 D (range: +1.37 to -3.62 D) at 1 month and -0.51?0.79 D (range: +1.25 to -4.50 D) at 1 year (Fig 3). At 1 month, the reduction in spherical equivalent refraction was statistically significant (P</001, t test for paired data, 95% confidence interval [CI] for the mean difference, -15.44 to -13.99).

At 12 months, spherical equivalent refraction was within ±0.50 D in 57.72% of eyes (71) and within ±1.00 D in 81.30% of eyes (100). (Spherical equivalent refraction was recorded in only 123 eyes at 12 months.) At 12 months, the refraction of piano was reached in 20.54% of cases. Figures 4 and 5 summarize the results of predictability.

At the last postoperative visit, UCVA was 20/40 or better in 108 (83.72%) eyes and 20/20 or better in 37 (28.68%) eyes (Fig 6). Best spectacle-corrected visual acuity improved by 2 or more Snellen lines in 68 (56.20%) eyes (Fig 7). No eye lost 2 or more Snellen lines of BSCVA.

The efficacy index was 1.18 ?0.43 at 6 months and 1.19?0.40 at 12 months; this difference was not statistically significant (P=. 179, Wilcoxon test for paired data). The safety index was 1.46?0.51 at 6 months and 1.37?0.46 at 12 months; this difference also was not statistically significant (P=. 825, Wilcoxon test for paired data).

INTRAOCULAR PRESSURE

Intraocular pressure increased in the early postoperative period and returned to preoperative levels at 3 months (Fig 8). Mean preoperative IOP was 14.50 ?2.74 mmHg and increased to 19.65 ? 7.49 mmHg at 1 week postoperatively; this difference was statistically significant (P<.001, Wilcox on test for paired data). One month postoperatively, mean IOP was still significantly higher than preoperatively (P<.001, WiIcoxon test for paired data).

Figure 7. Change in best spectacle -corrected visual acuity (BCVA) at 12 months after Implantation with the Kelman Duet phakic intraocular lens.TABLE 2Endothelial Morphometric Findings in 110 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*

Figure 7. Change in best spectacle -corrected visual acuity (BCVA) at 12 months after Implantation with the Kelman Duet phakic intraocular lens.

TABLE 2

Endothelial Morphometric Findings in 110 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*

CORNEAL ENDOTHELIUM

Endothelial morphometric data are shown in Table 2. Only the endothelial data from the coordinating center were analyzed because it was measured using the same accurate instrument (Konan SP5500) to be able to draw reliable conclusions for the purpose of this study. No statistically significant differences were found between preoperative and 3-month postoperative endothelial cell density (P=. 169, 95% CI -30.04 to 165.35, t test for paired data). There was no statistically significant reduction between 3 and 12 months postoperatively (P=.052, 95% CI -0.73 to 164.13, t test for paired data). However, preoperative endothelial density was higher than the 1-year postoperative measurement (P=.02, 95% CI 65.75 to 274.99, t test for paired data). Therefore, although there was a decrease in preoperative endothelial cell density and 3-month postoperative measurements, and between 3-month and 6-month postoperative measurements, the difference was not statistically significant for either time period. However, when preoperative and 12 -month postoperative measurements were compared, the total decrease in cell density is statistically significant. As in any study concerning the endothelial cell loss in PIOLs, longer follow-up is necessary to confirm this observation.

Additionally, there were statistically significant differences between coefficients of variation before and after surgery (P=.02, 95% CI 4.60 to 19.14 for preoperative to 3 months postoperative and P=. 06, 95% CI 2.82 to 15.81 for preoperative to 12 months postoperative, t test for paired data). However, no statistically significant difference was found between postoperative coefficients of variation (P=.151, 95% CI -6.36 to 1.03, t test for paired data).

Table

TABLE 3Short- and Long-term Complications in 169 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*

TABLE 3

Short- and Long-term Complications in 169 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*

Loss of endothelial cell density was ^15% in 19 (17.27%) eyes. Of these cases, pupil ovalization occurred in 8 (42.11%) eyes and the lens appeared decentered at the anterior segment in 6 (31.58%) eyes. In 4 (50.0%) of the eyes with pupil ovalization, the haptic was exchanged to improve the situation.

COMPLICATIONS

Surgery was completed successfully in all eyes with no intraoperative complications. The surgery was performed with no sutures. Postoperatively, no lens opacification, chronic increased IOP, or pupillary block occurred, and none of the lenses had to be explanted during the follow-up period. Short-term (3 months postoperatively) and long-term (12 months postoperatively) complications are shown in Table 3.

Initial Postoperative Period. These are complications related to the surgery and to the early postoperative period. Only 1 (0.59%) eye experienced synechiae between the iris and the optic of the lens in the early postoperative period; this was resolved by widening the iridotomy. Endothelial cell density loss was >20% in this eye. Additionally, significant flare reaction occurred in 1 (0.59%) eye at 1 month postoperatively but was resolved with injection of intracameral triamcinolone acetonide. This was necessary because the use of topical prednisolone did not resolve the inflammation. A cycloplegic also was prescribed to avoid synechiae and to alleviate the symptoms.

Mild and severe levels of pupil ovalization (Fig 9) were present in 17 (10.06%) eyes. Normally, this phenomenon is produced by inadequate adjustment of the total length of the haptic to the internal intertrabecular distance of the eye (Fig 10). For this reason, haptic exchange was performed in 9 (5.33%) eyes and haptic repositioning was performed in 3 (1.78%) eyes. Mild decentration of the lens could be appreciated by slit-lamp microscopy in 9 (5.33%) eyes. Night vision disturbances such as halos or glare were a significant complaint in 11.24% of eyes (19) at 1 month, but this frequency decreased to 4.73% of eyes (8) at 3 months postoperatively.

Figure 8. Change in intraocular pressure (IOP) after implantation with the Kelman Duet phakic intraocular lens. Error bars = ± standard deviation.Figure 9. Pupil ovalization after implantation with the Kelman Duet phakic intraocular lens.

Figure 8. Change in intraocular pressure (IOP) after implantation with the Kelman Duet phakic intraocular lens. Error bars = ± standard deviation.

Figure 9. Pupil ovalization after implantation with the Kelman Duet phakic intraocular lens.

Complications After 12 Months of Follow-up. In this study, complications that appeared during the last period of follow-up (1 year) are considered to be longterm complications. At 12 months postoperatively, no severe complications were present. The percentage of cases with pupil ovalization was similar to that at 3 months postoperatively. Haptic exchange was performed through sub-2.5-mm incisions in all cases that required exchange. Pupil ovalization was solved in all but one case in which haptic exchange possibly was performed late and iris ischemia was already present. Lens decentration was apparent in 11 (6.51%) eyes at 12 months postoperatively. Halos and glare were disturbing phenomena in 2 (1.18%) eyes. No retinal complications were noted.

Figure 10. Very high frequency ultrasound microscopie image showing the position of an implanted Kelman Duet lens with respect to the anterior segment structures (decente red) with the edges of the lens very near to the corneal endothelium.

Figure 10. Very high frequency ultrasound microscopie image showing the position of an implanted Kelman Duet lens with respect to the anterior segment structures (decente red) with the edges of the lens very near to the corneal endothelium.

DISCUSSION

The surgical correction of high myopia is a controversial issue. A better quality of vision compared with LASIK is achieved by implanting an anterior chamber PIOL in these cases. However, many questions remain about the long-term potential risks to the anterior segment structures. Phakic intraocular lenses must be located in a relatively small anatomic space, the anterior segment of the eye. These lenses should be well positioned, with adequate stability, so as not to damage the corneal endothelium and the anterior lens capsule.23 Therefore, accurate sizing and positioning are critical for a successful outcome.

Anterior chamber lenses provide excellent optical results,9111516'22 but many postoperative complications have been observed with several initial designs (especially the first generation). The following complications have been reported after implantation of an anterior chamber PIOL: significant endothelial cell density loss,17"19 pupillary block,10,29 iritis,10,21'30 endophthalmitis,31 vitreous hemorrhages,32 choroidal neovascularization,33,34 retinal detachment,2135 and ischemic optic neuropathy.36 Except for a case of significant inflammation reaction detected in our series, none of these complications have been observed during 12 months of follow-up. These results parallel the adequate tolerance to angle-supported PIOLs reported in previous studies.21,2237

Pupil ovalization is a common complication typical of angle-supported PIOLs.10,15,16,21 This problem has been associated with incorrect sizing of the phakic lens and areas of sectorial iris atrophy and ischemia.21,24,38 When ovalization occurs along the axis of the haptic footplate, the most probable cause is an unbalanced distribution of compression forces against the iris root that induces ischemic and inflammatory changes with iris retraction. The Kelman Duet lens has the potential to solve cases of pupil ovalization by exchanging the haptic of the lens postoperatively. The frequency of ovalization in this study was similar to that reported in studies of other types of angle-supported lenses (Table 4). However, the possibility of exchanging the haptic has facilitated the solution of pupil ovalization in several cases, and this feature is offered only by the Kelman Duet lens. The process of haptic exchange is as easy as the initial implantation using a bimanual technique; the haptic is disengaged from the optic and mobilized from underneath the optic without touching it and then the new haptic is introduced through the incision and placed correctly. In this study, the incision size remained sub-2.5-mm in all cases that required haptic exchange.

Pupil ovalization is a complication related to insufficient preoperative knowledge of the anterior segment anatomy. We must consider that the classic white-towhite distance, measured at the preoperative visit, is a poor predictor of the internal dimensions of the anterior segment. Specifically, the correlation of whiteto-white measurement to anterior chamber diameter or sulcus size is poor.39,40 This led us to choose an incorrect size of the phakic lens in some cases. For this reason, it is important to analyze the anterior segment structures and dimensions to achieve a good outcome after PIOL implantation. This is critical when the lens implanted is angle-supported because an oversized or undersized lens could lead to different complications, particularly pupil ovalization.

Table

TABLE 4Complications Reported in Studies Using Angle-supported Phakic Intraocular Lenses (PIOLs)TABLE 5Refractive Outcomes at 12-Month Follow-up Reported in Studies Using Phakic Intraocular Lenses (PIOLs)

TABLE 4

Complications Reported in Studies Using Angle-supported Phakic Intraocular Lenses (PIOLs)

TABLE 5

Refractive Outcomes at 12-Month Follow-up Reported in Studies Using Phakic Intraocular Lenses (PIOLs)

There are different methods that provide information regarding the configuration of the anterior segment and can delineate the exact dimensions of the space where the lens will be placed. Such methods include very high frequency (100 MHz) ultrasound biometry (Artemis; Ultralink LLC, St Petersburg, FIa), anterior segment optical coherence tomography (OCT scan; Carl Zeiss M?dit?e), high-frequency 50 MHz ultrasound microscopy (UBM 840; Zeiss-Humphrey Ine, Dublin, Calif), or Scheimpflug imaging. Therefore, further analysis of the anterior segment with any of these methods is crucial in the preoperative examination for PIOL candidates. Only in this way can an adequate PIOL be implanted for the anatomic condition of each eye, thereby optimizing the outcome and avoiding complications. Decentration of the PIOL was present in a small percentage of cases and may have been the result of incorrect preoperative lens size selection. We are referring exclusively to cases of decentration related to an unbalance of supporting forces of the lens due to inappropriate size or incorrect positioning. In three such cases, lens decentration was resolved by rotating the lens. In another two eyes with larger decentration and additional pupil ovalization, the problem was resolved by changing the dimensions of the haptic.

Table

TABLE 6Loss in Postoperative Corneal Endothelium Density Reported in Studies Using Phakic Intraocular Lenses (PIOLs)

TABLE 6

Loss in Postoperative Corneal Endothelium Density Reported in Studies Using Phakic Intraocular Lenses (PIOLs)

Photic phenomena with PIOLs depend on centrati on, the relationship between the pupil and optical zone, pupil deformity, PIOL design, and the refractive index.10 In our study, night vision disturbances such as halos or glare were a relatively frequent complaint in the early postoperative period. At 12 months postoperatively, significant halos or glare were present in only 2 (1.18%) cases. This finding is significantly lower than that reported in several studies with different types of angle-supported lenses (Table 4). One of the possible reasons for this excellent outcome is the larger effective optical zone (5.5 mm) provided by the Kelman Duet lens in comparison to the PIOL models (5.0 mm) implanted in previous studies. The low incidence of decentration (6.51%) of this lens also could be a factor that contributes to this excellent optical result.

Predictability of refractive results was good and comparable to or higher than that obtained in other studies (Table 5). As shown in Figure 4, there was a slight tendency to residual myopia. In addition, 77.27% (18) of the eyes that required LASIK retreatment had myopic astigmatism. The spherical correction could be improved by optimizing the calculations for obtaining the ideal lens power to be implanted.

The efficacy and safety indexes at 12 months for the Kelman Duet PIOL were high and showed an excellent optical result. The Kelman Duet PIOL has a similar safety index when compared with previous PIOL models but a higher efficacy index (Table 5). At 12 months, BSCVA improved by two or more Snellen lines in 56.20% of eyes, which means that BSCVA improved by more than one Snellen line in more than half of the cases in this study. In addition, the refractive results remained stable, with spherical equivalent refraction, efficacy, and safety indexes being maintained during the postoperative period (Table 1).

Changes in IOP are shown in Figure 8. In the immediate postoperative period, IOP increased significantly in some cases. At 3 months postoperatively, IOP returned to the preoperative level and remained constant until the final examination. This change correlates with findings reported for other PIOLs.9"1116'21 We believe this is a multifactorial phenomenon. The initial postoperative increase in IOP is related to surgical factors (ie, viscoelastic remains at the anterior chamber), whereas medium-term (10 days) elevation logically is due to the effect of topical steroid treatment.

At 12 months postoperatively, the mean loss of endothelial cell density was 5.43%. This implies a statistically significant reduction in endothelial density, but this finding is similar to the loss of endothelial cell density reported in recent studies with the new generation of anterior chamber PIOLs (Table 6). Phakic intraocular lenses may compromise the corneal endothelium for longer periods of time, and this finding must be viewed with caution until a study with long-term follow-up is available that confirms the safety of the lens for the corneal endothelium. Currently, the results of this study compare favorably to other PIOLs.

Damage to the endothelium while inserting the lens can occur prior to the unfolding of the implant, although damage will most likely occur during unfolding. The variability of this kind of damage depends largely on the surgeon's experience and should be accepted as inevitable. On the other hand, cell loss could happen by intermittent mechanical contact of the endothelium with the edges of the lens. This factor must be prevented by ensuring a minimum distance of 1.5 mm between the endothelium and the edge of the myopic optic,23 which will prevent a massive loss of endothelial cell density and continuous damage to the corneal integrity. The design of the Kelman Duet minimizes this risk by not flexing the lens against the peripheral endothelium.26 Pupil ovalization, as suggested in previous reports,24 appears to be a risk factor for the development of significant endothelial cell loss. In this study, almost half of the eyes with severe endothelial loss had associated pupil ovalization. It is possible that an incorrect position of the lens (associated frequently with pupil ovalization) may allow an intermittent and continuous touching of the endothelium with mechanical damage. If the lens is decentered or does not have the appropriate size (which is what happens with pupil ovalization), then the lens does not adopt a correct position and different portions of the lens could be nearer to the endothelium. For example, the lens could be displaced anteriorly and the edges of the lens may be close to or even touching the endothelium, thereby inducing more damage.

Finally, it is important to comment on the advantages of the optic exchangeability. The optical properties of the lens can be modified without changing the support of the lens because the haptic is not removed. If an angle-supported haptic behaves correctly in the eye, it is not worth changing it. It means that there is good support inside the eye for an additional optic to compensate for the defocus of the ocular system. If the haptic has adapted to the intraocular media (with no pupil ovalization, decentration, or inflammation reactions), it makes no sense to change the overall structure of the lens. We must take into account that several complications with the angle-supported lenses come from the inappropriate properties of the haptic. In our series, no optic exchange was necessary; however, optic exchange could be an excellent option, for example, for those eyes in which progression of myopia occurs or is expected. Removal of the optic also is quite simple and basically is accomplished by reversing the insertion maneuver. Hence, the surgeon can adapt the optic to the visual needs of the patient at any point in time in the patient's visual evolution, such as inserting a multifocal optic when presbyopia develops. This advantage has not been offered previously by any PIOL.

With the Kelman Duet lens, exchange of the optic or haptic elements is performed through a sub-2.5-mm incision; this feature is not offered by any other PIOL design, including posterior chamber PIOL designs. This potential exchangeability through such a small incision is a unique feature of this PIOL and requires further evaluation to prove its practicality in patients implanted with the Kelman Duet lens.

This study further supports our previous preliminary study26 regarding the Kelman Duet lens. This PIOL provides excellent refractive safety, efficacy, and predictability, with good intraocular stability 1 year after implantation. It offers the opportunity, by means of haptic exchange, to solve possible complications due to improper selection of the PIOL haptic size. Future application of this PIOL to address myopia or presbyopia associated with spherical error may be possible through the ability to exchange the haptic.

The lens provides excellent optical results for the correction of medium, high, and extreme myopia and offers the opportunity to make a refractive adjustment by changing the optic if necessary. Severe complications are rare, although a preoperative assessment of the anterior segment configuration is important for good selection of the lens size. The majority of problems derived from the implantation of PIOLs are the result of an incorrect relation between the PIOL size and the anterior chamber size.

The Kelman Duet PIOL offers a new alternative for phakic implants in refractive surgery, with distinct advantages for the patient and surgeon to optimize anatomical, refractive, and visual needs. The potential of exchangeability of the lens optic and haptic is relevant. All of the patients in our study who underwent implantation will reach a presbyopic age, and at that time, the optic can be changed to a multifocal optic. The exchangeability already has proven effective in this study for those cases in which pupil ovalization was resolved by exchanging the haptic. With any other lens, full explantation would have been necessary with the possibility of consequent risk for the intraocular structures.

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TABLE 1

Refractive Characteristics of 146 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*

Figure 3. Change in postoperative spherical equivalent refraction (SE) after implantation with the Kelman Duet phakic intraocular lens. Error bars = + standard deviation.

Figure 4. Intended spherical equivalent refraction (SE) versus achieved correction at 12 months after implantation with the Kelman Duet phakic intraocular lens.

TABLE 3

Short- and Long-term Complications in 169 Eyes That Underwent Implantation With the Kelman Duet Phakic Intraocular Lens*

TABLE 4

Complications Reported in Studies Using Angle-supported Phakic Intraocular Lenses (PIOLs)

TABLE 5

Refractive Outcomes at 12-Month Follow-up Reported in Studies Using Phakic Intraocular Lenses (PIOLs)

TABLE 6

Loss in Postoperative Corneal Endothelium Density Reported in Studies Using Phakic Intraocular Lenses (PIOLs)

10.3928/1081-597X-20071101-02

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