Myopic shift from the predicted refraction after sulcus fixation of PMMA posterior chamber intraocular lenses

Transcription

1 Myopic shift from the predicted refraction after sulcus fixation of PMMA posterior chamber intraocular lenses Hüseyin Bayramlar, MD; Ibrahim F. Hepsen, MD; Harun Yilmaz, MD ABSTRACT RÉSUMÉ Background: To evaluate the refractive results of sulcus-fixated polymethylmethacrylate (PMMA) posterior chamber intraocular lenses (PC IOLs) after cataract surgery with and without posterior capsule complications. Methods:The charts of patients who had undergone cataract surgery were reviewed, and eyes that had received sulcus-fixated PMMA PC IOLs were included in the study. Postoperative refraction, predicted postoperative refraction for in-the-bag IOL with the same diopter, intraoperative posterior capsular complications and vitrectomy, axial eye length, incision type (corneal or scleral), and surgery type were recorded and analyzed.the difference between actual postoperative refraction and predicted refraction for the in-the-bag lens was calculated for each patient. Results: Of 143 patients (84 men and 59 women), 162 eyes with a sulcus-fixated posterior chamber intraocular lens were investigated. Mean age was 63.7 ± 12.1 years. A mean myopic shift of 1.02 ± 0.96 D from the predicted in-the-bag refraction was found. There were no significant differences between eyes with or without vitreous loss vitrectomy (p = 0.8), eyes with scleral or corneal incisions (p = 0.11), and eyes having phacoemulsification or extracapsular cataract extraction (p = 0.93). In terms of axial length, there were no significant differences between long, normal, or short eyes (p = 0.85). Interpretation: Sulcus fixation of a PMMA IOL originally planned for in-thebag fixation caused approximately 1.00 D myopic shift in this study.we recommend that when sulcus fixation is necessary PMMA IOL power should be approximately 1.25 to 1.50 D less than the power for in-thebag fixation. Axial length, incision type, vitreous loss and use of vitrectomy, and type of the surgery do not appear to alter the postoperative refraction significantly in eyes with sulcus fixation. Contexte : Cette étude avait pour objet d évaluer les résultats réfractifs de la fixation dans le sulcus des LIO de polyméthylméthacrylate (PMMA) implantées dans la capsule postérieure, après une chirurgie de la cataracte, avec ou sans complication. Méthodes : Après examen des dossiers des patients qui avaient subi une chirurgie de la cataracte, on a retenu aux fins de l étude les yeux qui avaient reçu une LIO From the Inonu University, Turgut Özal Medical Center, Department of Ophthalmology, Malatya, Turkey Originally received May 5, 2005 Accepted for publication Nov. 14, 2005 Correspondence to: Dr. Hüseyin Bayramlar, Inonu University, Turgut Özal Medical Center, Department of Ophthalmology, Ataturk Mh, 14. Cd. Sena Ap. 47/7, Sehitkamil, Gaziantep, 27060, Turkey; This article has been peer-reviewed. Can J Ophthalmol 2006;41: Myopic shift after sulcus fixation Bayramlar et al

2 PMMA dans la chambre postérieur avec fixation dans le sulcus. L analyse a porté sur la réfraction postopératoire obtenue, la réfraction postopératoire prévue pour la fixation capsulaire avec même dioptrie, les complications peropératoires dans la capsule postérieure, la longueur de l axe visuel, le genre d incision (cornéenne ou sclérale) et le type d opération. L écart entre la réfraction postopératoire obtenue et la réfraction prévue pour la fixation capsulaire a été calculé pour chaque patient. Résultats : L on a étudié 162 yeux ayant reçu une lentille intraoculaire dans la chambre postérieure avec fixation dans le sulcus, chez 143 patients (84 hommes et 59 femmes). La moyenne d âge était de 63,7 ± 12,1 ans. L on a constaté un écart moyen de myopie de 1,02 ± 0,96 D en regard de la réfraction capsulaire prévue. Il n y avait pas d écart significatif entre les yeux avec ou sans perte de vitrée vitrectomie (p = 0,8), selon la nature sclérale ou cornéenne des incisions (p = 0,11) et la méthode d extraction de la cataracte (phacoémulsification ou extracapsulaire) (p = 0,93). Quant à la longueur de l axe visuel, il n y avait pas d écart significatif, qu elle soit longue, normale ou courte (p = 0,85). Interprétation : La fixation dans le sulcus d une LIO PMMA prévue pour fixation capsulaire a entraîné un écart myopique d environ 1,00 D, selon cette étude. Nous recommandons que, lorsque la fixation dans le sulcus s avère nécessaire, la puissance de LIO PMMA soit d environ 1,25 à 1,50 D inférieure à celle prévue pour fixation capsulaire. La longueur de l axe visuel, le type d incision, la perte de vitrée, le recours à la vitrectomie ou le genre de chirurgie ne semblent pas altérer la réfraction postopératoire de façon significative chez les yeux où la fixation se fait dans le sulcus. In-the-bag fixation of an intraocular lens (IOL) has been accepted as the preferred method for lens implantation, and yet there are few studies comparing in-the-bag and sulcus-fixated lenses. 1,2 During cataract surgery, capsular complications such as zonular dialysis, posterior capsule rupture, vitreous loss, or unsuccessful capsulorrhexis may prevent inthe-bag fixation of an IOL. In these cases, the IOL is usually implanted into the ciliary sulcus. Since a sulcus-fixated IOL is more anteriorly located than the intended in-the-bag fixation, resultant postoperative refraction shows a myopic shift from the predicted value. In such cases, surgeons generally subtract, empirically, 0.50 to 1.00 D from the predicted IOL power calculated preoperatively for in-the-bag fixation. However, there are few reports in the literature addressing this issue. 3 5 Recently, Suto et al reported that a significant myopic shift ( 0.78 D) from the predicted refraction occurred after sulcus fixation of the same acrylic IOL. 3 They concluded that the IOL power should be 1.00 D less for sulcus fixation than for in-the-bag fixation in eyes with a normal axial length. 3 Although foldable IOLs are the usual type of lens being implanted in developed countries, polymethylmethacrylate (PMMA) IOLs have been implanted extensively in many other countries because these IOLs are less expensive and their long-term safety has been proven over 50 years. In this study, we aimed to evaluate refractive outcomes of sulcus-fixated PMMA IOLs in eyes with and without posterior capsule complications in which in-the-bag fixation was not possible. METHODS The charts of patients who had undergone cataract surgery at our institution between 1998 and March 2004 were screened and patients having sulcusfixated PMMA IOLs were included into the study. The reason for sulcus fixation in these eyes was frequently posterior capsular rupture, and occasionally inability to do a successful capsulorrhexis. Phacoemulsification or extracapsular cataract extraction (ECCE) had been done through a corneal or scleral tunnel incision. All operations were primary IOL implantation; secondary lens implantations were not included. In cases with vitreous loss, a vitrectorassisted anterior vitrectomy was performed. The lens power used in the sulcus implantation was reduced from that originally calculated preoperatively for use in the bag. The lens power used in our calculations to compare the theoretical refraction of lens-in-the-bag CAN J OPHTHALMOL VOL. 41, NO. 1,

3 with the actual postoperative refraction was the same as that used in the sulcus implantation. Corneal incisions were closed with a 10-0 nylon suture; scleral ones with 8-0 absorbable polyglactine suture, or remained sutureless. The eyes were implanted with 2 models of intraocular lens: Alcon LC80BD (Alcon Laboratuvarlari, Istanbul, Turkey) and Nederlens PC 163 UV (Nederlens BV, Sidderburen, Netherlands). Both models of IOL were one-piece monoblock, C- looped PMMA posterior chamber (PC) IOLs. Alcon LC80BD has 5 anterior angulation. Its optic diameter is 6.25 mm and total diameter 13.0 mm. Manufacturer s suggested A constant is Nederlens PC 163 UV has 10 anterior angulation. Its optic diameter is 6.0 mm and total diameter 13.0 mm. Manufacturer s suggested A constant is We recorded incision type (corneal or scleral), axial eye length, postoperative refraction, predicted refraction for the same diopter in-the-bag IOL, and vitreous loss. The difference between actual postoperative refraction and predicted refraction for in-the-bag lens was calculated for each patient. The eyes were classified into 3 groups on the basis of axial length. Eyes with an axial length less than 21 mm were classed as short eyes, eyes with 21 to mm as normal, and eyes with 24 mm or longer as long eyes. We optimized the A constant for each model of lens for use in our clinic. An empirical study was performed with in-the-bag placement of both models. Postoperative refraction was measured at 3 months and a reverse calculation performed to obtain the optimized A constant. These optimized A constants were used for calculating refraction in eyes with sulcus implantation of IOLs. Subsequently, the refractive shift was calculated for each eye. Refractive and keratometric measurements were made with an Auto Refracto Keratometer KR-8100 (Topcon Inc., Tokyo, Japan). Axial lengths were measured while the patient was seated in an upright position, using B-scan ultrasonography in standardized A-mode with applanation technique (Biovision International, Clermont-Ferrand, France). A value of 1550 m/s was set for sound velocity. Ten axial length measurements were taken and the mean value was used for calculations. Biometric calculation of the IOL was performed with the SRK 2 linear regression formula. 4 The A constant recommended by the manufacturer was selected for each eye. Spherical equivalent value was assessed at least 3 months after sulcus fixation for refractive measurements. Refractive differences from the predicted refraction that exceeded ± 3.00 D were excluded from the study considering that these values may have been the result of biometric error or decentralization or tilt of the IOL rather than the result of implantation site. Data from eyes known to have decentralized or tilted IOLs were also excluded on the basis of the notes in the charts. The statistical analyses were done with SPSS 11.0 statistical software in Windows XP. The group distribution was tested with Kolmogorov Smirnov test (nonparametric test). For all groups distributed normally, parametric tests were used. A p value less than 0.05 was considered statistically significant. RESULTS Of 143 patients (84 men and 59 women), 162 eyes with sulcus-fixated PMMA PC IOLs were included into the study. The mean age of the patients was 63.7 ± 12.1 (range 18 90) years. The Alcon LC80BD lens was used in 97 eyes, and the Nederlens PC 163 UV lens in 65 eyes. Mean predicted refraction was ± 0.82 D, and mean postoperative spherical equivalent was 0.87 ± 1.20 D (p < 0.001, paired t test). Overall, a mean myopic shift of 1.02 ± 0.96 D from the predicted in-the-bag refraction was found after sulcus fixation. There was no significant difference between the eyes with and without vitreous loss vitrectomy. There was also no significant difference between the eyes having phacoemulsification and ECCE (p = 0.8). In terms of axial length, there was no significant difference between long, normal, and short eyes (p = 0.85, Kruskal Wallis analysis of variance). There was also no significant difference between the eyes with scleral and corneal incisions (p = 0.11). Table 1 shows the mean differences in spherical equivalents and the statistical test results in terms of vitreous loss vitrectomy, type of incision, type of surgery, and axial eye length. INTERPRETATION We found in this study that sulcus fixation of a PMMA IOL planned for in-the-bag fixation caused a myopic shift of approximately 1.00 D. There are few reports in the literature addressing this issue. 2,3 Suto et al reported a 0.78 D myopic shift from the predicted refraction after sulcus fixation of the same IOL. 3 One of the basic differences between Suto s study and ours is the type of IOL material. To our 80 CAN J OPHTHALMOL VOL. 41, NO. 1, 2006

4 knowledge, our report is the first investigating the refractive results of sulcus-fixated PMMA IOLs. It is possible that the greater myopic shift in our study occurred because an acrylic IOL may take a more posterior place in a vitrectomized eye than does a PMMA lens. Suto and coauthors used one type of surgery (phacoemulsification) and one model of IOL (Acrysof, Alcon) in eyes with normal axial length of 30 patients selected for bilateral cataract surgery. 3 Their patients had sulcus fixation in one eye and in-the-bag fixation in the fellow eye. Hence the inclusion criteria were markedly distinct. Although the present study is more heterogeneous, it has a larger number of patients. We included eyes having both phacoemulsification and ECCE, corneal and scleral incisions, with and without vitreous loss, and eyes with short, normal, and long axial lengths because we thought that these extended inclusion criteria would be useful for a better understanding of the influence of possible contributors to refractive differences. We found that none of them influenced the extent of the postoperative myopic shift. Suto et al concluded that the IOL power should be 1.00 D less for sulcus fixation than for in-the-bag fixation in eyes with a normal axial length. 3 Hayashi et al suggested a 0.50 D reduction in the intended power for sulcus fixation. 2 According to our study, the IOL power should be reduced by approximately 1.25 to 1.50 D from that of in-the-bag fixation. Apart from the IOL material, other possibilities accounting for this difference include various surgical techniques and incision types, and different lens manufacturers. Vitreous loss and the use of vitrectomy do not appear to cause a marked change in postoperative refraction in eyes with sulcus-fixated instead of inthe-bag IOLs, according to our study. On a theoretical basis, it would be reasonable to predict some difference between the eyes with and without vitreous loss; but in our study, we did not observe this result. To our knowledge, there are no reports on that topic in the literature. It is known that the change in IOL power is affected by axial length, since the relative depth of the anterior chamber correlates moderately with axial length. Consequently, one could reasonably expect that the short eyes would show more errors in refraction postoperatively, and that the differences in axial length would influence the differences in refraction. Table 1 Difference between predicted spherical equivalent for in-the-bag intraocular lens and actual spherical equivalent after sulcus fixation In their study, Suto et al empirically suggest a 1.50 to 2.00 D reduction for short eyes and a 0.50 D or no reduction for long eyes, although they did not include short and long eyes in their study. 3 We did not find a significant difference, however, between the refractive shift of the normal, short, and long eyes, in spite of the small number of short eyes. The reason that there was no difference between the refractive shift of a sulcus-placed lens versus an inthe-bag lens in normal, short, and long eyes may be that the anterior segment size does not correlate exactly with axial length. 6 We are aware that many confounding factors can affect postoperative refractive results, for example, biometric errors, manufacturers errors, axial eye length, corneal astigmatism, or surgeon-related factors. On the other hand, we believe this study provides useful information on the myopic shift in sulcus-fixated PC IOLs. Further studies investigating the same variables in larger patient populations will be helpful to better understand the extent of the myopic shift of sulcus-fixated lenses. REFERENCES Difference in SE,* diopters Axial length < 21 mm 0.99 ± Axial length mm 1.03 ± Axial length > 24 mm 0.98 ± With vitreous loss 1.05 ± Without vitreous loss 1.00 ± Corneal incision 0.90 ± Scleral incision 1.14 ± Phacoemulsification 1.00 ± ECCE 1.02 ± All eyes 1.02 ± <0.001 Note: Difference in SE = actual spherical equivalent predicted spherical equivalent; ECCE = extracapsular cataract extraction. 1. Apple DJ, Reidy JJ, Googe JM, et al. A comparison of ciliary sulcus and capsular bag fixation of posterior chamber intraocular lenses. J Am Intraocul Implant Soc 1985;11: n p CAN J OPHTHALMOL VOL. 41, NO. 1,

5 2. Hayashi K, Hayashi H, Nakao F, Hayashi F. Intraocular lens tilt and decentration, anterior chamber depth, and refractive error after trans-scleral suture fixation surgery. Ophthalmology 1999;106: Suto C, Hori S, Fukuyama E, Akura J. Adjusting intraocular lens power for sulcus fixation. J Cataract Refract Surg 2003; 29: Sanders DR, Retzlaff JA, Kraff MC, Gimbel HV, Raanan MG. Comparison of the SRK/T formula and other theoretical and regression formulas. J Cataract Refract Surg 1990;16: Osher RHJ. Adjusting intraocular lens power for sulcus fixation. J Cataract Refract Surg 2004;30: Holladay JT, Gills JP, Leidlen J, Cherchio M. Achieving emmetropia on extremely short eyes with two piggyback posterior chamber intraocular lenses. Ophthalmology 1996;103: Key words: sulcus fixation, polymethylmethacrylate, intraocular lens, spherical equivalent 82 CAN J OPHTHALMOL VOL. 41, NO. 1, 2006