- Email: [email protected]
Improved Refractive Outcome for Ciliary Sulcus-Implanted Intraocular Lenses
Improved Refractive Outcome for Ciliary Sulcus-Implanted Intraocular Lenses Rahul Dubey, BSc (Med), MBBS (Hons), MMed,1 Wayne Birchall, FRANZCO,2 John Grigg, MBBS, FRANZCO, FRACS1 Objective: To investigate the ideal correction of intraocular lens (IOL) power for sulcus implantation. Design: Retrospective, comparative case series. Participants: The records of 679 patients undergoing cataract surgery from June 2007 to June 2008 were reviewed. Intervention: Eyes in this series underwent phacoemulsification and IOL implantation with local anesthesia. Patients in our study population had their IOL power reduced by 0.5 or 1 diopter (D) from that calculated by the SRK-T formula for in-the-bag implantation. The IOL implanted was the foldable 3-piece acrylic Acrysof MA60AC (Alcon Laboratories Inc., Fort Worth, TX). Main Outcome Measures: In each case, the difference between actual spherical equivalent (SE) refraction and that predicted by biometry using the SRK-T formula was calculated. Results: Posterior capsule tears requiring implantation of IOL in the ciliary sulcus occurred in 36 eyes. When comparing eyes in which the power was reduced by 0.5 D with those in which the reduction was 1.0 D, those with a power reduction of 1.0 D had significantly less unexpected error (0.49 vs. 1.01 D SE). After stratifying eyes by axial length (AL), we found higher unexpected refractive error in short eyes (⬍22 mm AL). Likewise, eyes with a predicted IOL power ⬎25 D had a greater postoperative refractive error. Conclusions: This is the first comparative clinical review examining adjustment of power of the sulcusimplanted IOL. We found that the IOL power should be adjusted according to the measured AL and predicted IOL power. For patients with a predicted IOL power from 18 to 25 D, power should be reduced by at least 1 D; for lenses ⬎25 D, power should be reduced by 1.5 to 2 D. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. Ophthalmology 2012;119:261–265 © 2012 by the American Academy of Ophthalmology.
Posterior capsular (PC) tear is the most common complication of phacoemulsification cataract surgery.1–3 Posterior capsular tears occur at different rates depending on both patient and surgeon factors. The rate is approximately 0.76%4 for experienced surgeons and 1.75% to 4%3,5 for junior surgeons. Therefore, the phacoemulsification surgeon learning curve6 is a significant risk factor for PC tears. In view of the incidence of complications, however rare, it is important to have a systematic approach to optimizing visual outcome. This is critical for the patient but also for the opportunity to train new surgeons in phacoemulsification. After capsular tear, implantation of the intraocular lens (IOL) in the ciliary sulcus provides an excellent anatomic option.7 To achieve a final visual outcome including refraction in the range discussed preoperatively with the patient requires an adjustment based on the effect of the new anatomic location of the IOL. The sulcus-implanted IOL has a more anterior effective lens position. The effective power of the IOL therefore increases; thus, the spherical equivalent (SE) shows a myopic shift from the preoperative predicted value. The power of the new IOL must be changed to reflect the new location. The extent of the influence of a change in IOL position is also predicted to alter with differences in axial length (AL).8 Currently there is little consensus on how much the power must be changed.9 –14 © 2012 by the American Academy of Ophthalmology Published by Elsevier Inc.
We compared the refractive outcome when the IOL power was reduced by 0.5 or 1 diopter (D) before implantation in the sulcus. We aimed to identify the preferred adjustment in IOL power for sulcus fixation and thus achieve a visual outcome close to the preoperative expectation of both the patient and the surgeon.
Patients and Methods We conducted a literature search using MEDLINE, EMBASE, and PubMed for the keywords phacoemulsification, posterior capsule rupture, complication, and sulcus. All studies had their abstracts reviewed by R.D., and a bibliographic search of relevant published articles was conducted. Institutional review board and ethics committee approval was obtained. Ethics approval included investigation of the complication rate and its relationship to the experience of the surgeon. We conducted a retrospective chart review of all patients admitted for phacoemulsification cataract surgery at the Sydney Eye Hospital, New South Wales, Australia, between June 2007 and June 2008. We included all patients who had posterior capsule rupture during cataract surgery, and sulcus fixation of an IOL was selected as the method of optical correction. All patients underwent a comprehensive eye examination preoperatively, including measurement of best-corrected visual acuity, refraction, and intraocular pressure. The presence or absence of diabetes, hypertension, and pseudoexfoliation, and the degree of myopia ISSN 0161-6420/12/$–see front matter doi:10.1016/j.ophtha.2011.07.050
261
Ophthalmology Volume 119, Number 2, February 2012 were recorded. Lens opacity was classified as cortical, posterior subcapsular, nuclear sclerosis, or a combination based on slit-lamp examination and graded per the Lens Opacities Classification System III classification.15 The IOL power was calculated preoperatively using biometry measured with a noncontact partial coherence interferometer (IOL Master; Carl Zeiss Meditec, Jena, Germany). Routine phacoemulsification was performed through a 2.5- to 3-mm corneal incision. After the posterior capsule ruptured, an assessment was made as to the amount of cortical and nuclear lens fragments remaining. The individual surgeon determined the most appropriate means of removing the residual lens material. Any vitreous in the anterior segment was removed via an anterior vitrectomy. The state of the lens capsule bag was assessed. In patients in whom there was sufficient anterior capsule support, an IOL was inserted in the ciliary sulcus. Patients in our study population had their IOL power reduced by 0.5 or 1 D from the IOL power calculated by the SRK-T16 formula for in-the-bag implantation. The decision to reduce IOL power was made at the discretion of the operating surgeon. These cases form the basis of this study. The IOL available on tender to the unit for sulcus implantation was the foldable 3-piece acrylic IOL MA60AC (Alcon Laboratories Inc., Fort Worth, TX), which has a 6.0-mm optic and a loop-to-loop diameter of 13 mm. A standardized postoperative assessment form was completed, including best-corrected visual acuity and postoperative refraction at 3 months (at least 2 weeks after removal of any corneal sutures) and any postoperative complications. Automated refractive and keratometric measurements were made with a refractometer/keratometer KR-8100 (Topcon Inc., Tokyo, Japan). We recorded the power of IOL chosen preoperatively for capsular bag implantation and the associated predicted postoperative spherical equivalent refraction (SER), the power of IOL actually implanted in the ciliary sulcus, postoperative SER, AL, and vitreous loss. The difference between actual and predicted postoperative SER was calculated for each patient and termed the “refractive shift.” Patients were excluded from the study if there was an accompanying secondary procedure (e.g., trabeculectomy). Statistical analyses were performed with SPSS 11.0 (SPSS Inc., Chicago, IL). Chi-square and t tests were used to compare the study groups. A P value less than 0.05 was considered statistically significant.
Table 2. Patient Characteristics and Postoperative Results Characteristic
Result
Mean AL Mean planned IOL power (D) Mean sulcus fixed IOL power (D) Mean predicted refraction (SE) Mean actual refraction after sulcus IOL with a 0.5 or 1 D reduction in power (SE)
23.55 ⫾ 1.15 23.36 ⫾ 1.45 22.55 ⫾ 1.35 ⫺0.45 ⫾ 0.23 ⫺1.16 ⫾ 0.47
AL ⫽ axial length; D ⫽ diopter; IOL ⫽ intraocular lens; SE⫽ spherical equivalent.
conversion of the tear into a stable round capsulorrhexis. Sulcus fixation of the IOL was selected in 36 patients. An anterior chamber IOL was placed in 1 patient when the IOL was not adequately supported by the ciliary sulcus. There were 367 male patients (54.1%) and 312 female patients (45.9%) with a mean age of 74.5⫾10.6 (range 44 –94) years (Table 1). In the sulcus fixation group, the mean predicted postsurgical refraction was ⫺0.45 D SE and the mean planned IOL power was 23.36 D. The mean power of the actual implanted IOL was 22.55 D, and the mean actual refraction was ⫺1.16 D SE (Table 2). The mean “refractive shift” toward myopia was lower after a 1 D IOL power reduction than after a 0.5 D reduction (Fig 1). There
Results Of 679 eyes in 679 patients, 46 eyes had a PC tear. Placement of the IOL in the capsular bag was possible in 9 patients, with Table 1. Risk Factors for Posterior Capsular Tear in Complicated versus Uncomplicated Eyes
Variable Age (yrs) Male/female Consultant/senior trainee/ junior trainee AL ⬎25 mm (%) Pseudoexfoliation (%) Diabetes mellitus (%) Systemic hypertension (%)
PC Tear Group (n ⴝ 36)
Uncomplicated Surgery Group (n ⴝ 633)
P Value
77.9 ⫾ 6.4 14/22 6/10/20
71.3 ⫾ 8.8 347/286 101/376/156
⬍0.05* ⬍0.05* ⬍0.05*
8.3 31.6 55.5 27.7
3.4 12.9 17.9 21.4
⬍0.05* ⬍0.05* ⬍0.05* 0.08*
AL ⫽ axial length; PC ⫽ posterior capsular. *Chi-square test for frequency values.
262
Figure 1. Diagram demonstrating the unexpected myopia (SE) after sulcus implantation of an IOL lens with 1 D power less than that calculated for in-the-bag fixation. Compared with when the lens power was reduced by 0.5 D, reduction by 1 D results in an improved refractive outcome. D ⫽ diopter; IOL ⫽ intraocular lens; SE ⫽ spherical equivalent.
Dubey et al 䡠 Adjusting IOL Power for Sulcus Implantation Table 3. Difference between Predicted Spherical Equivalent for In-the-Bag Intraocular Lens and Actual Spherical Equivalent after Sulcus Fixation
AL ⬍22 mm AL 22–25 mm AL ⬎25 mm
IOL Power Reduced by 0.5 D
No.
1.82 ⫾ 0.47 0.86 ⫾ 0.29 0.42 ⫾ 0.31
7 10 5
IOL Power Reduced by 1.0 D
No.
P Value
1.01 ⫾ 0.32 0.38 ⫾ 0.20
3 11
⬍0.05* ⬍0.05*
AL ⫽ axial length; D ⫽ diopters; IOL ⫽ intraocular lens. *Paired t tests for mean values.
was a significant association among the AL, amount of postoperative refractive shift, and postoperative SER (Table 3). The mean refractive shift, and thus the degree of postoperative myopia, was greater for eyes classified with short AL ⬍22 mm (⫺1.82 D) than eyes classified with normal AL 22 to 26 mm (⫺0.86 D) or long AL ⬎26 mm (⫺0.42 D). This difference was apparent in eyes having had their lens power reduced by 0.5 or 1 D for sulcus implantation. For both IOL power groups, the mean refractive shift was greater after 0.5 D IOL power reduction than after a 1 D reduction. Patients with a higher calculated power for their IOL (⬎25 D) had a significantly higher myopic postoperative refractive error than those with lower IOL powers (18 –25 D). The mean refractive shift was higher in the ⬎25 D planned IOL power group (⫺1.41 D) than in the 18 –25 D planned IOL power group (⫺0.67 D) (Table 4). This difference was apparent in eyes with their lens power reduced by 0.5 or 1 D for sulcus implantation. For both IOL power groups, the mean refractive shift was greater after 0.5 D IOL power reduction than after 1 D reduction. Comparison of the mean refractive shift between patients who had their IOL power reduced by 0.5 D and patients whose IOL power was reduced by 1 D shows less myopic refractive shift in the latter (Fig 1). There was a significant association between the AL and the amount of postoperative refractive error (Table 3). Eyes classified as short (AL ⬍22 mm) had a higher postoperative refractive error than those classified as normal (AL 22–26 mm) or long (AL ⬎26 mm). Patients with a high (⬎25 D) calculated power for their IOL had a significantly larger postoperative refractive error. The mean difference in SE was higher in the ⬎25 D planned IOL power group (⫺1.41 D SE) than in the ⬍25 D planned IOL power group (⫺0.67 D SE) (Table 4). This occurred despite having had their lens power reduced by 0.5 or 1 D before implantation in the sulcus.
Discussion Phacoemulsification surgery is a safe and effective procedure. However, there are situations in which complications are more likely to occur. First, patient and cataract characteristics, such as age, male gender, presence of glaucoma, diabetic retinopathy, hypermature cataract, AL ⬎26 mm, and pseudoexfoliation, have been shown to be significant risk factors.4 Second, surgical skill level and experience are determinants of the risk of complications. Once a complication occurs, the challenge is to minimize the effects on the patient’s final visual outcome.17 If managed correctly, the visual outcomes for patients are not compromised.3 In this situation, there is a need for a systematic approach to optimize visual outcomes when sulcus implantation of the IOL is required. During complicated cataract surgery with PC rupture, the IOL may be placed in the capsular bag, a 3-piece IOL may be placed in the ciliary sulcus, or an IOL may be placed in the anterior chamber.18 Sulcus fixation may be selected in the presence of an intact anterior capsule when there is insufficient posterior capsule support for placement in the capsular bag.18 This is the surgical philosophy at our institution (Sydney Eye Hospital). The aim of this study is to determine how to adjust the power of the sulcus-implanted IOL to improve the postoperative refractive outcome. Refractive and visual acuity outcomes after sulcus placement have been rarely studied. The IOL is placed in the sulcus, which is more anteriorly located than the capsule bag; therefore, the effective power of the optic increases. Theoretically, to achieve the same postoperative refraction, a lower-power IOL would be required for sulcus placement. Both transverse displacement and tilt of an implanted lens are more likely to occur with sulcus fixation19 and may also cause myopic shift, but this is relatively small compared with the effect of longitudinal positional errors. Refractive errors are related linearly to the magnitude of longitudinal displacement and to the square of the magnitude of tilt or transverse displacement.20 It has been previously calculated that a ⫺1.4 D spherical refractive error would result from forward displacement of a 21 D IOL (calculated to produce postoperative emmetropia) by 1 mm.21 In addition, the size of these errors increase for thicker (i.e., higher dioptric powered) lenses because of a greater effectivity for a
Table 4. Difference between Predicted Spherical Equivalent for In-the-Bag Intraocular Lens and Actual Spherical Equivalent after Sulcus Fixation IOL Power Reduced by 0.5 D
No.
IOL Power Reduced by 1.0 D
No.
P Value
0.11 ⫾ 0.21 0.67 ⫾ 0.38 1.41 ⫾ 0.53
3 13 6
0.37 ⫾ 0.14 0.8 ⫾ 0.21
10 4
⬍0.05* ⬍0.05*
Predicted IOL power ⬍18 D Predicted IOL power 18–25 D Predicted IOL power ⬎25 D D ⫽ diopters; IOL ⫽ intraocular lens. *Paired t tests for mean values.
263
Ophthalmology Volume 119, Number 2, February 2012 thick lens.8 An additional adjustment should therefore be made for IOLs with higher powers. Surgeons are generally advised to subtract, empirically, 0.5 to 1.0 D from the predicted IOL power calculated preoperatively for in-the-bag fixation. Significant confusion exists as to the correct amount of power reduction to achieve the best possible refractive outcome postoperatively. There are guidelines available that are theoretic,22 based on the IOL power as the major determinant of postoperative refractive outcome. Studies have also been based on computer simulation, which have again shown that power should be reduced by 0.510 or 1.0 D.11 Published clinical research data directly comparing these 2 approaches are lacking. In our study, surgeons subtracted 0.5 or 1 D from the power calculated for in-the-bag fixation. The decision was made on the basis of the clinical judgment of the surgeon. Individual surgeons have formulated their preference on the basis of the conventional teaching delivered at conference presentations since the 1990s.14 At that time, an adjustment of 0.5 D for sulcus fixation was recommended. Newer literature that is based on theoretic and computer simulation recommends a reduction of 1.0 D in IOL power when sulcus fixation is selected.11 Our study seems to be the first to assess the refractive outcome when the power of the IOL was actually reduced (by 0.5 or 1 D) for ciliary sulcus fixation. The studies in the literature examine the effect of IOL implantation in the ciliary sulcus rather than the outcome of adjusting the IOL power for ciliary sulcus implantation. We have shown that, although a reduction in IOL power of 1 D generally resulted in less postoperative myopia than a reduction of 0.5 D, some eyes (shorter AL, higher calculated IOL power) are still left with a significantly myopic refraction. Therefore, on the basis of our results, we would recommend the following refinement of IOL power adjustments to minimize postoperative myopia after complicated cataract surgery with PC rupture requiring ciliary sulcus fixation of the IOL: For planned IOL power ⬍18 D, power should be reduced by 0.5 D. For planned IOL power from 18 to 25 D, power should be reduced by at least 1 D. For planned IOL power ⬎25 D ⫾ eyes with an AL ⬍22 mm, power should be reduced by 1.5 to 2 D. (A range is given to allow for greater reduction for higher-power planned lenses or shorter ALs.) In conclusion, although the aim will usually be to achieve a postoperative refraction close to that chosen for a particular eye (which may not necessarily be emmetropia), even in complicated cases, a low degree of myopia is generally preferable to hyperopia. In the study population, application of these recommendations would be unlikely to result in a hyperopic postoperative refraction. Many factors can confound the accurate determination of IOL power and the accurate measurement of postoperative refractive results. This study provides useful information in guiding decision making when adjusting the
264
power of an IOL to be implanted in the ciliary sulcus to minimize an unexpected refractive shift.
References 1. Zaidi FH, Corbett MC, Burton BJ, Bloom PA. Raising the benchmark for the 21st century—the 1000 cataract operations audit and survey: outcomes, consultant-supervised training and sourcing NHS choice. Br J Ophthalmol 2007;91:731– 6. 2. Desai P, Minassian DC, Reidy A. National Cataract Surgery Survey 1997-8: a report of the results of the clinical outcomes. Br J Ophthalmol 1999;83:1336 – 40. 3. Dubey R, Chan K, Lertsumitkul S, et al. Cataract surgery outcomes in NSW, Australia. Asian J Ophthalmol. Asian J Ophthalmol 2011;12:124 –9. 4. Narendran N, Jaycock P, Johnston RL, et al. The Cataract National Dataset electronic multicentre audit of 55,567 operations: risk stratification for posterior capsule rupture and vitreous loss. Eye (Lond) 2009;23:31–7. 5. Jaycock P, Johnston RL, Taylor H, et al. The Cataract National Dataset electronic multi-centre audit of 55,567 operations: updating benchmark standards of care in the United Kingdom and internationally. Eye (Lond) 2009;23: 38 – 49. 6. Randleman JB, Wolfe JD, Woodward M, et al. The resident surgeon phacoemulsification learning curve. Arch Ophthalmol 2007;125:1215–9. 7. Wagoner MD, Cox TA, Ariyasu RG, et al, Ophthalmic Technology Assessment Committee Anterior Segment Panel. Intraocular lens implantation in the absence of capsular support: a report by the American Academy of Ophthalmology. Ophthalmology 2003;110:840 –59. 8. Olsen T. Calculation of intraocular lens power: a review. Acta Ophthalmol Scand 2007;85:472– 85. 9. Knox Cartwright NE, Aristodemou P, Sparrow JM, Johnston RL. Adjustment of intraocular lens power for sulcus implantation [letter]. J Cataract Refract Surg 2011;37:798 –9; author reply 799 – 800. 10. Spokes DM, Norris JH, Ball JL. Refinement of lens power selection for sulcus placement of intraocular lens [letter]. J Cataract Refract Surg 2010;36:1436 –7. 11. Suto C, Hori S, Fukuyama E, Akura J. Adjusting intraocular lens power for sulcus fixation. J Cataract Refract Surg 2003; 29:1913–7. 12. Bayramlar H, Hepsen IF, Yilmaz H. Myopic shift from the predicted refraction after sulcus fixation of PMMA posterior chamber intraocular lenses. Can J Ophthalmol 2006;41: 78 – 82. 13. 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;106:878 – 82. 14. Osher RH. Adjusting intraocular lens power for sulcus fixation [letter]. J Cataract Refract Surg 2004;30:2031; author reply 2031. 15. Chylack LT Jr, Wolfe JK, Singer DM, et al, Longitudinal Study of Cataract Study Group. The Lens Opacities Classification System III. Arch Ophthalmol 1993;111:831– 6. 16. Sanders DR, Retzlaff JA, Kraff MC, et al. Comparison of the SRK/T formula and other theoretical and regression formulas. J Cataract Refract Surg 1990;16:341– 6.
Dubey et al 䡠 Adjusting IOL Power for Sulcus Implantation 17. Frost NA, Sparrow JM, Strong NP, Rosenthal AR. Vitreous loss in planned extracapsular cataract extraction does lead to a poorer visual outcome. Eye (Lond) 1995;9:446 –51. 18. Gimbel HV, Sun R, Ferensowicz M, et al. Intraoperative management of posterior capsule tears in phacoemulsification and intraocular lens implantation. Ophthalmology 2001;108: 2186 –9; discussion 2190 –2. 19. Atchison DA. Refractive errors induced by displacement of intraocular lenses within the pseudophakic eye. Optom Vis Sci 1989;66:146 –52.
20. Atchison DA. Optical design of intraocular lenses. III. On-axis performance in the presence of lens displacement. Optom Vis Sci 1989;66:671– 81. 21. Giers U, Epple C, Schutte E. Flattening of the anterior chamber and myopic results in sulcus fixation of posterior chamber lenses [in German]. Klin Monbl Augenheilkd 1989;195: 353–5. 22. East Valley Ophthalmology (doctor-hill.com) IOL Power Calculations: Bag vs. Sulcus IOL Power. Available at: http://www. doctor-hill.com/iol-main/bag-sulcus.htm. Accessed March 5, 2011.
Footnotes and Financial Disclosures Originally received: April 8, 2011. Final revision: July 27, 2011. Accepted: July 27, 2011. Available online: December 23, 2011.
Manuscript no. 2011-550.
1
Save Sight Institute, Discipline of Ophthalmology Sydney Medical School, The University of Sydney, Sydney Eye Hospital Campus, Sydney, Australia.
2
Whangarei Hospital, Northland District Health Board, Whangarei, New Zealand.
This material is under consideration for presentation at the American Academy of Ophthalmology Annual Meeting, October 2011. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. Correspondence: Rahul Dubey, BSc (Med), MBBS (Hons), MMed, The University of Sydney, Department of Ophthalmology, Sydney Eye Hospital, Save Sight Institute, 8 Macquarie Street, Sydney, NSW 2000 Australia. E-mail: [email protected].
265
Posterior capsular (PC) tear is the most common complication of phacoemulsification cataract surgery.1–3 Posterior capsular tears occur at different rates depending on both patient and surgeon factors. The rate is approximately 0.76%4 for experienced surgeons and 1.75% to 4%3,5 for junior surgeons. Therefore, the phacoemulsification surgeon learning curve6 is a significant risk factor for PC tears. In view of the incidence of complications, however rare, it is important to have a systematic approach to optimizing visual outcome. This is critical for the patient but also for the opportunity to train new surgeons in phacoemulsification. After capsular tear, implantation of the intraocular lens (IOL) in the ciliary sulcus provides an excellent anatomic option.7 To achieve a final visual outcome including refraction in the range discussed preoperatively with the patient requires an adjustment based on the effect of the new anatomic location of the IOL. The sulcus-implanted IOL has a more anterior effective lens position. The effective power of the IOL therefore increases; thus, the spherical equivalent (SE) shows a myopic shift from the preoperative predicted value. The power of the new IOL must be changed to reflect the new location. The extent of the influence of a change in IOL position is also predicted to alter with differences in axial length (AL).8 Currently there is little consensus on how much the power must be changed.9 –14 © 2012 by the American Academy of Ophthalmology Published by Elsevier Inc.
We compared the refractive outcome when the IOL power was reduced by 0.5 or 1 diopter (D) before implantation in the sulcus. We aimed to identify the preferred adjustment in IOL power for sulcus fixation and thus achieve a visual outcome close to the preoperative expectation of both the patient and the surgeon.
Patients and Methods We conducted a literature search using MEDLINE, EMBASE, and PubMed for the keywords phacoemulsification, posterior capsule rupture, complication, and sulcus. All studies had their abstracts reviewed by R.D., and a bibliographic search of relevant published articles was conducted. Institutional review board and ethics committee approval was obtained. Ethics approval included investigation of the complication rate and its relationship to the experience of the surgeon. We conducted a retrospective chart review of all patients admitted for phacoemulsification cataract surgery at the Sydney Eye Hospital, New South Wales, Australia, between June 2007 and June 2008. We included all patients who had posterior capsule rupture during cataract surgery, and sulcus fixation of an IOL was selected as the method of optical correction. All patients underwent a comprehensive eye examination preoperatively, including measurement of best-corrected visual acuity, refraction, and intraocular pressure. The presence or absence of diabetes, hypertension, and pseudoexfoliation, and the degree of myopia ISSN 0161-6420/12/$–see front matter doi:10.1016/j.ophtha.2011.07.050
261
Ophthalmology Volume 119, Number 2, February 2012 were recorded. Lens opacity was classified as cortical, posterior subcapsular, nuclear sclerosis, or a combination based on slit-lamp examination and graded per the Lens Opacities Classification System III classification.15 The IOL power was calculated preoperatively using biometry measured with a noncontact partial coherence interferometer (IOL Master; Carl Zeiss Meditec, Jena, Germany). Routine phacoemulsification was performed through a 2.5- to 3-mm corneal incision. After the posterior capsule ruptured, an assessment was made as to the amount of cortical and nuclear lens fragments remaining. The individual surgeon determined the most appropriate means of removing the residual lens material. Any vitreous in the anterior segment was removed via an anterior vitrectomy. The state of the lens capsule bag was assessed. In patients in whom there was sufficient anterior capsule support, an IOL was inserted in the ciliary sulcus. Patients in our study population had their IOL power reduced by 0.5 or 1 D from the IOL power calculated by the SRK-T16 formula for in-the-bag implantation. The decision to reduce IOL power was made at the discretion of the operating surgeon. These cases form the basis of this study. The IOL available on tender to the unit for sulcus implantation was the foldable 3-piece acrylic IOL MA60AC (Alcon Laboratories Inc., Fort Worth, TX), which has a 6.0-mm optic and a loop-to-loop diameter of 13 mm. A standardized postoperative assessment form was completed, including best-corrected visual acuity and postoperative refraction at 3 months (at least 2 weeks after removal of any corneal sutures) and any postoperative complications. Automated refractive and keratometric measurements were made with a refractometer/keratometer KR-8100 (Topcon Inc., Tokyo, Japan). We recorded the power of IOL chosen preoperatively for capsular bag implantation and the associated predicted postoperative spherical equivalent refraction (SER), the power of IOL actually implanted in the ciliary sulcus, postoperative SER, AL, and vitreous loss. The difference between actual and predicted postoperative SER was calculated for each patient and termed the “refractive shift.” Patients were excluded from the study if there was an accompanying secondary procedure (e.g., trabeculectomy). Statistical analyses were performed with SPSS 11.0 (SPSS Inc., Chicago, IL). Chi-square and t tests were used to compare the study groups. A P value less than 0.05 was considered statistically significant.
Table 2. Patient Characteristics and Postoperative Results Characteristic
Result
Mean AL Mean planned IOL power (D) Mean sulcus fixed IOL power (D) Mean predicted refraction (SE) Mean actual refraction after sulcus IOL with a 0.5 or 1 D reduction in power (SE)
23.55 ⫾ 1.15 23.36 ⫾ 1.45 22.55 ⫾ 1.35 ⫺0.45 ⫾ 0.23 ⫺1.16 ⫾ 0.47
AL ⫽ axial length; D ⫽ diopter; IOL ⫽ intraocular lens; SE⫽ spherical equivalent.
conversion of the tear into a stable round capsulorrhexis. Sulcus fixation of the IOL was selected in 36 patients. An anterior chamber IOL was placed in 1 patient when the IOL was not adequately supported by the ciliary sulcus. There were 367 male patients (54.1%) and 312 female patients (45.9%) with a mean age of 74.5⫾10.6 (range 44 –94) years (Table 1). In the sulcus fixation group, the mean predicted postsurgical refraction was ⫺0.45 D SE and the mean planned IOL power was 23.36 D. The mean power of the actual implanted IOL was 22.55 D, and the mean actual refraction was ⫺1.16 D SE (Table 2). The mean “refractive shift” toward myopia was lower after a 1 D IOL power reduction than after a 0.5 D reduction (Fig 1). There
Results Of 679 eyes in 679 patients, 46 eyes had a PC tear. Placement of the IOL in the capsular bag was possible in 9 patients, with Table 1. Risk Factors for Posterior Capsular Tear in Complicated versus Uncomplicated Eyes
Variable Age (yrs) Male/female Consultant/senior trainee/ junior trainee AL ⬎25 mm (%) Pseudoexfoliation (%) Diabetes mellitus (%) Systemic hypertension (%)
PC Tear Group (n ⴝ 36)
Uncomplicated Surgery Group (n ⴝ 633)
P Value
77.9 ⫾ 6.4 14/22 6/10/20
71.3 ⫾ 8.8 347/286 101/376/156
⬍0.05* ⬍0.05* ⬍0.05*
8.3 31.6 55.5 27.7
3.4 12.9 17.9 21.4
⬍0.05* ⬍0.05* ⬍0.05* 0.08*
AL ⫽ axial length; PC ⫽ posterior capsular. *Chi-square test for frequency values.
262
Figure 1. Diagram demonstrating the unexpected myopia (SE) after sulcus implantation of an IOL lens with 1 D power less than that calculated for in-the-bag fixation. Compared with when the lens power was reduced by 0.5 D, reduction by 1 D results in an improved refractive outcome. D ⫽ diopter; IOL ⫽ intraocular lens; SE ⫽ spherical equivalent.
Dubey et al 䡠 Adjusting IOL Power for Sulcus Implantation Table 3. Difference between Predicted Spherical Equivalent for In-the-Bag Intraocular Lens and Actual Spherical Equivalent after Sulcus Fixation
AL ⬍22 mm AL 22–25 mm AL ⬎25 mm
IOL Power Reduced by 0.5 D
No.
1.82 ⫾ 0.47 0.86 ⫾ 0.29 0.42 ⫾ 0.31
7 10 5
IOL Power Reduced by 1.0 D
No.
P Value
1.01 ⫾ 0.32 0.38 ⫾ 0.20
3 11
⬍0.05* ⬍0.05*
AL ⫽ axial length; D ⫽ diopters; IOL ⫽ intraocular lens. *Paired t tests for mean values.
was a significant association among the AL, amount of postoperative refractive shift, and postoperative SER (Table 3). The mean refractive shift, and thus the degree of postoperative myopia, was greater for eyes classified with short AL ⬍22 mm (⫺1.82 D) than eyes classified with normal AL 22 to 26 mm (⫺0.86 D) or long AL ⬎26 mm (⫺0.42 D). This difference was apparent in eyes having had their lens power reduced by 0.5 or 1 D for sulcus implantation. For both IOL power groups, the mean refractive shift was greater after 0.5 D IOL power reduction than after a 1 D reduction. Patients with a higher calculated power for their IOL (⬎25 D) had a significantly higher myopic postoperative refractive error than those with lower IOL powers (18 –25 D). The mean refractive shift was higher in the ⬎25 D planned IOL power group (⫺1.41 D) than in the 18 –25 D planned IOL power group (⫺0.67 D) (Table 4). This difference was apparent in eyes with their lens power reduced by 0.5 or 1 D for sulcus implantation. For both IOL power groups, the mean refractive shift was greater after 0.5 D IOL power reduction than after 1 D reduction. Comparison of the mean refractive shift between patients who had their IOL power reduced by 0.5 D and patients whose IOL power was reduced by 1 D shows less myopic refractive shift in the latter (Fig 1). There was a significant association between the AL and the amount of postoperative refractive error (Table 3). Eyes classified as short (AL ⬍22 mm) had a higher postoperative refractive error than those classified as normal (AL 22–26 mm) or long (AL ⬎26 mm). Patients with a high (⬎25 D) calculated power for their IOL had a significantly larger postoperative refractive error. The mean difference in SE was higher in the ⬎25 D planned IOL power group (⫺1.41 D SE) than in the ⬍25 D planned IOL power group (⫺0.67 D SE) (Table 4). This occurred despite having had their lens power reduced by 0.5 or 1 D before implantation in the sulcus.
Discussion Phacoemulsification surgery is a safe and effective procedure. However, there are situations in which complications are more likely to occur. First, patient and cataract characteristics, such as age, male gender, presence of glaucoma, diabetic retinopathy, hypermature cataract, AL ⬎26 mm, and pseudoexfoliation, have been shown to be significant risk factors.4 Second, surgical skill level and experience are determinants of the risk of complications. Once a complication occurs, the challenge is to minimize the effects on the patient’s final visual outcome.17 If managed correctly, the visual outcomes for patients are not compromised.3 In this situation, there is a need for a systematic approach to optimize visual outcomes when sulcus implantation of the IOL is required. During complicated cataract surgery with PC rupture, the IOL may be placed in the capsular bag, a 3-piece IOL may be placed in the ciliary sulcus, or an IOL may be placed in the anterior chamber.18 Sulcus fixation may be selected in the presence of an intact anterior capsule when there is insufficient posterior capsule support for placement in the capsular bag.18 This is the surgical philosophy at our institution (Sydney Eye Hospital). The aim of this study is to determine how to adjust the power of the sulcus-implanted IOL to improve the postoperative refractive outcome. Refractive and visual acuity outcomes after sulcus placement have been rarely studied. The IOL is placed in the sulcus, which is more anteriorly located than the capsule bag; therefore, the effective power of the optic increases. Theoretically, to achieve the same postoperative refraction, a lower-power IOL would be required for sulcus placement. Both transverse displacement and tilt of an implanted lens are more likely to occur with sulcus fixation19 and may also cause myopic shift, but this is relatively small compared with the effect of longitudinal positional errors. Refractive errors are related linearly to the magnitude of longitudinal displacement and to the square of the magnitude of tilt or transverse displacement.20 It has been previously calculated that a ⫺1.4 D spherical refractive error would result from forward displacement of a 21 D IOL (calculated to produce postoperative emmetropia) by 1 mm.21 In addition, the size of these errors increase for thicker (i.e., higher dioptric powered) lenses because of a greater effectivity for a
Table 4. Difference between Predicted Spherical Equivalent for In-the-Bag Intraocular Lens and Actual Spherical Equivalent after Sulcus Fixation IOL Power Reduced by 0.5 D
No.
IOL Power Reduced by 1.0 D
No.
P Value
0.11 ⫾ 0.21 0.67 ⫾ 0.38 1.41 ⫾ 0.53
3 13 6
0.37 ⫾ 0.14 0.8 ⫾ 0.21
10 4
⬍0.05* ⬍0.05*
Predicted IOL power ⬍18 D Predicted IOL power 18–25 D Predicted IOL power ⬎25 D D ⫽ diopters; IOL ⫽ intraocular lens. *Paired t tests for mean values.
263
Ophthalmology Volume 119, Number 2, February 2012 thick lens.8 An additional adjustment should therefore be made for IOLs with higher powers. Surgeons are generally advised to subtract, empirically, 0.5 to 1.0 D from the predicted IOL power calculated preoperatively for in-the-bag fixation. Significant confusion exists as to the correct amount of power reduction to achieve the best possible refractive outcome postoperatively. There are guidelines available that are theoretic,22 based on the IOL power as the major determinant of postoperative refractive outcome. Studies have also been based on computer simulation, which have again shown that power should be reduced by 0.510 or 1.0 D.11 Published clinical research data directly comparing these 2 approaches are lacking. In our study, surgeons subtracted 0.5 or 1 D from the power calculated for in-the-bag fixation. The decision was made on the basis of the clinical judgment of the surgeon. Individual surgeons have formulated their preference on the basis of the conventional teaching delivered at conference presentations since the 1990s.14 At that time, an adjustment of 0.5 D for sulcus fixation was recommended. Newer literature that is based on theoretic and computer simulation recommends a reduction of 1.0 D in IOL power when sulcus fixation is selected.11 Our study seems to be the first to assess the refractive outcome when the power of the IOL was actually reduced (by 0.5 or 1 D) for ciliary sulcus fixation. The studies in the literature examine the effect of IOL implantation in the ciliary sulcus rather than the outcome of adjusting the IOL power for ciliary sulcus implantation. We have shown that, although a reduction in IOL power of 1 D generally resulted in less postoperative myopia than a reduction of 0.5 D, some eyes (shorter AL, higher calculated IOL power) are still left with a significantly myopic refraction. Therefore, on the basis of our results, we would recommend the following refinement of IOL power adjustments to minimize postoperative myopia after complicated cataract surgery with PC rupture requiring ciliary sulcus fixation of the IOL: For planned IOL power ⬍18 D, power should be reduced by 0.5 D. For planned IOL power from 18 to 25 D, power should be reduced by at least 1 D. For planned IOL power ⬎25 D ⫾ eyes with an AL ⬍22 mm, power should be reduced by 1.5 to 2 D. (A range is given to allow for greater reduction for higher-power planned lenses or shorter ALs.) In conclusion, although the aim will usually be to achieve a postoperative refraction close to that chosen for a particular eye (which may not necessarily be emmetropia), even in complicated cases, a low degree of myopia is generally preferable to hyperopia. In the study population, application of these recommendations would be unlikely to result in a hyperopic postoperative refraction. Many factors can confound the accurate determination of IOL power and the accurate measurement of postoperative refractive results. This study provides useful information in guiding decision making when adjusting the
264
power of an IOL to be implanted in the ciliary sulcus to minimize an unexpected refractive shift.
References 1. Zaidi FH, Corbett MC, Burton BJ, Bloom PA. Raising the benchmark for the 21st century—the 1000 cataract operations audit and survey: outcomes, consultant-supervised training and sourcing NHS choice. Br J Ophthalmol 2007;91:731– 6. 2. Desai P, Minassian DC, Reidy A. National Cataract Surgery Survey 1997-8: a report of the results of the clinical outcomes. Br J Ophthalmol 1999;83:1336 – 40. 3. Dubey R, Chan K, Lertsumitkul S, et al. Cataract surgery outcomes in NSW, Australia. Asian J Ophthalmol. Asian J Ophthalmol 2011;12:124 –9. 4. Narendran N, Jaycock P, Johnston RL, et al. The Cataract National Dataset electronic multicentre audit of 55,567 operations: risk stratification for posterior capsule rupture and vitreous loss. Eye (Lond) 2009;23:31–7. 5. Jaycock P, Johnston RL, Taylor H, et al. The Cataract National Dataset electronic multi-centre audit of 55,567 operations: updating benchmark standards of care in the United Kingdom and internationally. Eye (Lond) 2009;23: 38 – 49. 6. Randleman JB, Wolfe JD, Woodward M, et al. The resident surgeon phacoemulsification learning curve. Arch Ophthalmol 2007;125:1215–9. 7. Wagoner MD, Cox TA, Ariyasu RG, et al, Ophthalmic Technology Assessment Committee Anterior Segment Panel. Intraocular lens implantation in the absence of capsular support: a report by the American Academy of Ophthalmology. Ophthalmology 2003;110:840 –59. 8. Olsen T. Calculation of intraocular lens power: a review. Acta Ophthalmol Scand 2007;85:472– 85. 9. Knox Cartwright NE, Aristodemou P, Sparrow JM, Johnston RL. Adjustment of intraocular lens power for sulcus implantation [letter]. J Cataract Refract Surg 2011;37:798 –9; author reply 799 – 800. 10. Spokes DM, Norris JH, Ball JL. Refinement of lens power selection for sulcus placement of intraocular lens [letter]. J Cataract Refract Surg 2010;36:1436 –7. 11. Suto C, Hori S, Fukuyama E, Akura J. Adjusting intraocular lens power for sulcus fixation. J Cataract Refract Surg 2003; 29:1913–7. 12. Bayramlar H, Hepsen IF, Yilmaz H. Myopic shift from the predicted refraction after sulcus fixation of PMMA posterior chamber intraocular lenses. Can J Ophthalmol 2006;41: 78 – 82. 13. 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;106:878 – 82. 14. Osher RH. Adjusting intraocular lens power for sulcus fixation [letter]. J Cataract Refract Surg 2004;30:2031; author reply 2031. 15. Chylack LT Jr, Wolfe JK, Singer DM, et al, Longitudinal Study of Cataract Study Group. The Lens Opacities Classification System III. Arch Ophthalmol 1993;111:831– 6. 16. Sanders DR, Retzlaff JA, Kraff MC, et al. Comparison of the SRK/T formula and other theoretical and regression formulas. J Cataract Refract Surg 1990;16:341– 6.
Dubey et al 䡠 Adjusting IOL Power for Sulcus Implantation 17. Frost NA, Sparrow JM, Strong NP, Rosenthal AR. Vitreous loss in planned extracapsular cataract extraction does lead to a poorer visual outcome. Eye (Lond) 1995;9:446 –51. 18. Gimbel HV, Sun R, Ferensowicz M, et al. Intraoperative management of posterior capsule tears in phacoemulsification and intraocular lens implantation. Ophthalmology 2001;108: 2186 –9; discussion 2190 –2. 19. Atchison DA. Refractive errors induced by displacement of intraocular lenses within the pseudophakic eye. Optom Vis Sci 1989;66:146 –52.
20. Atchison DA. Optical design of intraocular lenses. III. On-axis performance in the presence of lens displacement. Optom Vis Sci 1989;66:671– 81. 21. Giers U, Epple C, Schutte E. Flattening of the anterior chamber and myopic results in sulcus fixation of posterior chamber lenses [in German]. Klin Monbl Augenheilkd 1989;195: 353–5. 22. East Valley Ophthalmology (doctor-hill.com) IOL Power Calculations: Bag vs. Sulcus IOL Power. Available at: http://www. doctor-hill.com/iol-main/bag-sulcus.htm. Accessed March 5, 2011.
Footnotes and Financial Disclosures Originally received: April 8, 2011. Final revision: July 27, 2011. Accepted: July 27, 2011. Available online: December 23, 2011.
Manuscript no. 2011-550.
1
Save Sight Institute, Discipline of Ophthalmology Sydney Medical School, The University of Sydney, Sydney Eye Hospital Campus, Sydney, Australia.
2
Whangarei Hospital, Northland District Health Board, Whangarei, New Zealand.
This material is under consideration for presentation at the American Academy of Ophthalmology Annual Meeting, October 2011. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. Correspondence: Rahul Dubey, BSc (Med), MBBS (Hons), MMed, The University of Sydney, Department of Ophthalmology, Sydney Eye Hospital, Save Sight Institute, 8 Macquarie Street, Sydney, NSW 2000 Australia. E-mail: [email protected].
265