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Refractive error with optimum intraocular lens power calculation after glaucoma filtering surgery
Refractive error with optimum intraocular lens power calculation after glaucoma filtering surgery Hsin-Yuan Tan, MD, Shiu-Chen Wu, MD Purpose: To assess the possibility of deriving an optimum intraocular lens (IOL) power after previous successful trabeculectomy. Setting: Chang Gung Memorial Hospital, Linko, Taiwan. Methods: The retrospective study included 1 eye of 22 patients who had cataract surgery after successful trabeculectomy performed by 1 surgeon. Twenty-two eyes that had cataract surgery only performed by the same surgeon were paired as a control group. The IOL power was calculated by the Sanders-Retzlaff-Kraff regression analysis formula based on the data derived after trabeculectomy. The postoperative refractive error at least 1 month after cataract surgery was recorded, and the difference was analyzed by a paired t test and 2-sample t test. Results: Cataract surgery combined with trabeculectomy resulted in a mean spherical equivalent of ÿ0.33 diopter 6 1.58 (SD). This was not significantly different from the predicted refractive error or the result in the control group (PO.05). Conclusion: Although the fluctuation in pseudophakic axial length measurement after glaucoma filtering surgery was logical, a predictable pseudophakic refractive outcome was derived clinically once the intraocular pressure stabilized after trabeculectomy. J Cataract Refract Surg 2004; 30:2595–2597 ª 2004 ASCRS and ESCRS
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ombined trabeculectomy and cataract removal is increasingly being performed in appropriate cases.1 Patients who do not have significant cataract at the time of the glaucoma procedure are inappropriate candidates for combined surgery. When pseudophakic rehabilitation is undertaken, the accuracy of intraocular lens (IOL) power calculation is essential. However, there is a larger spread in pseudophakic refractive error, which tends to be more myopic. The
Accepted for publication March 23, 2004. From the Department of Ophthalmology, Chang Gung Memorial Hospital, Linko, Taiwan. Presented at the 41st Annual Meeting of the Ophthalmological Society of Taiwan, Taipei, Taiwan, November 2000. None of the authors has a financial or proprietary interest in any material or method mentioned. Reprint requests to Shiu-Chen Wu, MD, Department of Ophthalmology, Chang Gung Memorial Hospital, No. 5, Fu-Shin Street, Kwuei-Shang Shiang, TaoYuan, Taiwan. E-mail: shiuchen@adm. cgmh.org.tw. ª 2004 ASCRS and ESCRS Published by Elsevier Inc.
documented fluctuation in axial length measurements after glaucoma and anterior segment surgery, especially in young patients and those with myopia, postoperative hypotony, and exposure to antimetabolites,2 led to the suggestion that IOL power calculation should be based on axial length measurements taken before trabeculectomy is performed. To explore this, we performed a retrospective review of our clinical experience concerning possible pseudophakic refractive errors in patients who had cataract surgery after trabeculectomy. The IOL power was calculated based on data obtained after trabeculectomy.
Patients and Methods The retrospective study comprised patients from Chang Gung Memorial Hospital, Linko, Taiwan, from 1995 through 2000. Measurements were collected from 22 patients who had phacoemulsification cataract surgery via a clear corneal or scleral tunnel incision after successful trabeculectomy. All operations were performed by the same surgeon 0886-3350/04/$-see front matter doi:10.1016/j.jcrs.2004.05.016
PSEUDOPHAKIC REFRACTIVE ERROR AFTER TRABECULECTOMY
(S.C.W.). Ophthalmic examinations before cataract surgery were visual acuity, refractive status, intraocular pressure (IOP), slitlamp biomicroscopy, direct ophthalmoscopy, and A-scan biometry. Calculation of IOL power was by the Sanders-Retzlaff-Kraff regression analysis formula. A minimum of 1 month after surgery, visual acuity, refractive status, and IOP measurements were recorded. Antiglaucoma medication given before or after cataract surgery was recorded. Twenty-two patients who received only phacoemulsification performed by the same surgeon were paired as the control group. The difference between the actual refraction and the predicted value and between refraction in the control group was analyzed by a paired t test and 2-sample t test, respectively.
Results Of the 22 patients having phacoemulsification after successful trabeculectomy, 8 were men and 14 were women. The mean age at the time of surgery was 67.2 years (range 37 to 89 years). The reasons for the surgeries were primary open-angle glaucoma (n Z 7), primary angle-closure glaucoma (n Z 14), and secondary glaucoma (n Z 1). No patient received adjuvant antimetabolite treatment. The mean IOP before trabeculectomy under maximum antiglaucoma medication was 24.1 mm Hg 6 6.3 (SD). The trabeculectomies and cataract surgeries were separated by 6 months to 10 years. The mean IOP after trabeculectomy but before cataract surgery was 12.4 6 3.0 mm Hg. Three cases required topical antiglaucoma medication after trabeculectomy. The best spectacle-corrected visual acuity before cataract surgery ranged from hand motions at 20 cm to 20/100. The mean IOL power chosen (corrected A-constant Z 118.5) was 22.4 6 3.3 diopters (D) and the mean predicted spherical equivalent (SE), ÿ0.09 6 0.57 D. The mean interval between cataract surgery and postoperative follow-up was 5.6 months (range 1 to 25 months). After cataract surgery, the mean IOP was 11.5 6 2.9 mm Hg. Four cases required topical antiglaucoma medication to maintain the IOP within the normal range. The mean difference between IOP before cataract surgery and IOP after cataract surgery was ÿ0.7 6 3.8 mm Hg. The postoperative best corrected visual acuity ranged from counting fingers at 10 cm to 20/20, and the mean SE was ÿ0.33 6 1.58 D. The postoperative SE was not statistically different from the predicted SE (PO.05, paired t test) or from the SE in 2596
the control group (mean ÿ0.20 6 0.86 D) (PO.05, 2-sample t test).
Discussion Successful pseudophakic rehabilitation after glaucoma filtering surgery requires accurate IOL power calculation. Axial length measurement may be crucial when a regression analysis formula is used for this calculation. However, axial length can change after trabeculectomy2–4 and nonpenetrating glaucoma filtering surgery.4 Decreases in axial length of 0.15 to 0.91 mm have been reported.2,5,6 The decrease may positively correlate with the significant IOP reduction that results from external outflow of aqueous humor through a surgical fistula.5,6 A thickened choroid accompanying low IOP might also influence axial length measurement.7 Cashwell and Martin2 noted a larger spread in pseudophakic refractive error, which tended to be more myopic, as well as a fluctuation in axial length after glaucoma and anterior segment surgery. It was concluded that IOL power calculation should be based on the axial length measurement taken before trabeculectomy. However, pretrabeculectomy axial length measurements are not always available when cataract surgery occurs some time later. In our study, the pseudophakic refractive errors in patients whose IOL power calculations were derived from the posttrabeculectomy axial length measurement were not statistically significantly different than the predicted refractive status or refraction in the control group. Explanations include decreased hypotony after trabeculectomy and IOP fluctuations before and after cataract surgery. Another study2 documented 12 patients with complications of low IOP after trabeculectomy who presented with significant changes in axial length (ÿ0.842 mm) compared to patients who were free of complications. Unfortunately, the study did not report the IOP change after cataract surgery. This parameter may be the crucial determining factor in the fluctuation in axial length measurement and pseudophakic refractive error after cataract surgery. Several studies,8–12 including ours, have documented a variable, but minimal, effect of phacoemulsification on IOP after trabeculectomy. The data is equivocal, with a reported slight increase, a decrease, or no change. In our study, the mean difference between
J CATARACT REFRACT SURG—VOL 30, DECEMBER 2004
PSEUDOPHAKIC REFRACTIVE ERROR AFTER TRABECULECTOMY
IOP before and after cataract surgery was ÿ0.7 6 3.8 mm Hg. Therefore, the corresponding fluctuation in axial length measurements before and after cataract surgery should theoretically be less significant if IOP stabilizes after trabeculectomy. Fluctuation in IOP and axial length measurements before and after cataract surgery might be expected to be less significant than before trabeculectomy and after cataract surgery once the IOP becomes stable after trabeculectomy. Thus, it is reasonable to expect less significant pseudophakic refractive error with cataract surgery when the IOP stabilizes after trabeculectomy. The disparity in the axial length change in our patients who received cataract surgery after glaucoma filtering surgery was logical. Nonetheless, preoperative lens measurements can give a predictable refractive outcome after the IOP stabilizes.
References 1. Tanito M, Ohira A, Chihara E. Surgical outcome of combined trabeculotomy and cataract surgery. J Glaucoma 2001; 10:302–308 2. Cashwell LF, Martin CA. Axial length decrease accompanying successful glaucoma filtration surgery. Ophthalmology 1999; 106:2307–2311 3. Kook MS, Kim HB, Lee SU. Short-term effect of mitomycin-C augmented trabeculectomy on axial length and corneal astigmatism. J Cataract Refract Surg 2001; 27: 518–523
4. Brown SVL. Discussion of the article by Cashwell and Martin: Axial length decrease accompanying successful glaucoma filtration surgery. Ophthalmology 1999; 106: 2311 ¨ , Ates H, Andac¸ K, Deli B. Axial length ¨ retmen O 5. U changes accompanying successful nonpenetrating glaucoma filtration surgery. Ophthalmologica 2003; 217: 199–203 6. Dickens MA, Cashwell LF. Long-term effect of cataract extraction on the function of an established filtering bleb. Ophthalmic Surg Lasers 1996; 27:9–14 7. Byrne SF, Green RL. Ultrasound of the Eye and Orbit. St Louis, MO, Mosby Year Book, 1992; 79–80 8. Casson RJ, Riddell CE, Rahman R, et al. Long-term effect of cataract surgery on intraocular pressure after trabeculectomy; extracapsular extraction versus phacoemulsification. J Cataract Refract Surg 2002; 28:2159– 2164 9. Tong JT, Miller KM. Intraocular pressure change after sutureless phacoemulsification and foldable posterior chamber lens implantation. J Cataract Refract Surg 1998; 24:256–262 10. Derbolav A, Vass C, Menapace R, et al. Long-term effect of phacoemulsification on intraocular pressure after trabeculectomy. J Cataract Refract Surg 2002; 28:425–430 11. Manoj B, Chako D, Khan MY. Effect of extracapsular cataract extraction and phacoemulsification performed after trabeculectomy on intraocular pressure. J Cataract Refract Surg 2000; 26:75–78 12. Mietz H, Andresen A, Welsandt G, Krieglstein GK. Effect of cataract surgery on intraocular pressure in eyes with previous trabeculectomy. Graefes Arch Clin Exp Ophthalmol 2001; 239:763–769
J CATARACT REFRACT SURG—VOL 30, DECEMBER 2004
2597
C
ombined trabeculectomy and cataract removal is increasingly being performed in appropriate cases.1 Patients who do not have significant cataract at the time of the glaucoma procedure are inappropriate candidates for combined surgery. When pseudophakic rehabilitation is undertaken, the accuracy of intraocular lens (IOL) power calculation is essential. However, there is a larger spread in pseudophakic refractive error, which tends to be more myopic. The
Accepted for publication March 23, 2004. From the Department of Ophthalmology, Chang Gung Memorial Hospital, Linko, Taiwan. Presented at the 41st Annual Meeting of the Ophthalmological Society of Taiwan, Taipei, Taiwan, November 2000. None of the authors has a financial or proprietary interest in any material or method mentioned. Reprint requests to Shiu-Chen Wu, MD, Department of Ophthalmology, Chang Gung Memorial Hospital, No. 5, Fu-Shin Street, Kwuei-Shang Shiang, TaoYuan, Taiwan. E-mail: shiuchen@adm. cgmh.org.tw. ª 2004 ASCRS and ESCRS Published by Elsevier Inc.
documented fluctuation in axial length measurements after glaucoma and anterior segment surgery, especially in young patients and those with myopia, postoperative hypotony, and exposure to antimetabolites,2 led to the suggestion that IOL power calculation should be based on axial length measurements taken before trabeculectomy is performed. To explore this, we performed a retrospective review of our clinical experience concerning possible pseudophakic refractive errors in patients who had cataract surgery after trabeculectomy. The IOL power was calculated based on data obtained after trabeculectomy.
Patients and Methods The retrospective study comprised patients from Chang Gung Memorial Hospital, Linko, Taiwan, from 1995 through 2000. Measurements were collected from 22 patients who had phacoemulsification cataract surgery via a clear corneal or scleral tunnel incision after successful trabeculectomy. All operations were performed by the same surgeon 0886-3350/04/$-see front matter doi:10.1016/j.jcrs.2004.05.016
PSEUDOPHAKIC REFRACTIVE ERROR AFTER TRABECULECTOMY
(S.C.W.). Ophthalmic examinations before cataract surgery were visual acuity, refractive status, intraocular pressure (IOP), slitlamp biomicroscopy, direct ophthalmoscopy, and A-scan biometry. Calculation of IOL power was by the Sanders-Retzlaff-Kraff regression analysis formula. A minimum of 1 month after surgery, visual acuity, refractive status, and IOP measurements were recorded. Antiglaucoma medication given before or after cataract surgery was recorded. Twenty-two patients who received only phacoemulsification performed by the same surgeon were paired as the control group. The difference between the actual refraction and the predicted value and between refraction in the control group was analyzed by a paired t test and 2-sample t test, respectively.
Results Of the 22 patients having phacoemulsification after successful trabeculectomy, 8 were men and 14 were women. The mean age at the time of surgery was 67.2 years (range 37 to 89 years). The reasons for the surgeries were primary open-angle glaucoma (n Z 7), primary angle-closure glaucoma (n Z 14), and secondary glaucoma (n Z 1). No patient received adjuvant antimetabolite treatment. The mean IOP before trabeculectomy under maximum antiglaucoma medication was 24.1 mm Hg 6 6.3 (SD). The trabeculectomies and cataract surgeries were separated by 6 months to 10 years. The mean IOP after trabeculectomy but before cataract surgery was 12.4 6 3.0 mm Hg. Three cases required topical antiglaucoma medication after trabeculectomy. The best spectacle-corrected visual acuity before cataract surgery ranged from hand motions at 20 cm to 20/100. The mean IOL power chosen (corrected A-constant Z 118.5) was 22.4 6 3.3 diopters (D) and the mean predicted spherical equivalent (SE), ÿ0.09 6 0.57 D. The mean interval between cataract surgery and postoperative follow-up was 5.6 months (range 1 to 25 months). After cataract surgery, the mean IOP was 11.5 6 2.9 mm Hg. Four cases required topical antiglaucoma medication to maintain the IOP within the normal range. The mean difference between IOP before cataract surgery and IOP after cataract surgery was ÿ0.7 6 3.8 mm Hg. The postoperative best corrected visual acuity ranged from counting fingers at 10 cm to 20/20, and the mean SE was ÿ0.33 6 1.58 D. The postoperative SE was not statistically different from the predicted SE (PO.05, paired t test) or from the SE in 2596
the control group (mean ÿ0.20 6 0.86 D) (PO.05, 2-sample t test).
Discussion Successful pseudophakic rehabilitation after glaucoma filtering surgery requires accurate IOL power calculation. Axial length measurement may be crucial when a regression analysis formula is used for this calculation. However, axial length can change after trabeculectomy2–4 and nonpenetrating glaucoma filtering surgery.4 Decreases in axial length of 0.15 to 0.91 mm have been reported.2,5,6 The decrease may positively correlate with the significant IOP reduction that results from external outflow of aqueous humor through a surgical fistula.5,6 A thickened choroid accompanying low IOP might also influence axial length measurement.7 Cashwell and Martin2 noted a larger spread in pseudophakic refractive error, which tended to be more myopic, as well as a fluctuation in axial length after glaucoma and anterior segment surgery. It was concluded that IOL power calculation should be based on the axial length measurement taken before trabeculectomy. However, pretrabeculectomy axial length measurements are not always available when cataract surgery occurs some time later. In our study, the pseudophakic refractive errors in patients whose IOL power calculations were derived from the posttrabeculectomy axial length measurement were not statistically significantly different than the predicted refractive status or refraction in the control group. Explanations include decreased hypotony after trabeculectomy and IOP fluctuations before and after cataract surgery. Another study2 documented 12 patients with complications of low IOP after trabeculectomy who presented with significant changes in axial length (ÿ0.842 mm) compared to patients who were free of complications. Unfortunately, the study did not report the IOP change after cataract surgery. This parameter may be the crucial determining factor in the fluctuation in axial length measurement and pseudophakic refractive error after cataract surgery. Several studies,8–12 including ours, have documented a variable, but minimal, effect of phacoemulsification on IOP after trabeculectomy. The data is equivocal, with a reported slight increase, a decrease, or no change. In our study, the mean difference between
J CATARACT REFRACT SURG—VOL 30, DECEMBER 2004
PSEUDOPHAKIC REFRACTIVE ERROR AFTER TRABECULECTOMY
IOP before and after cataract surgery was ÿ0.7 6 3.8 mm Hg. Therefore, the corresponding fluctuation in axial length measurements before and after cataract surgery should theoretically be less significant if IOP stabilizes after trabeculectomy. Fluctuation in IOP and axial length measurements before and after cataract surgery might be expected to be less significant than before trabeculectomy and after cataract surgery once the IOP becomes stable after trabeculectomy. Thus, it is reasonable to expect less significant pseudophakic refractive error with cataract surgery when the IOP stabilizes after trabeculectomy. The disparity in the axial length change in our patients who received cataract surgery after glaucoma filtering surgery was logical. Nonetheless, preoperative lens measurements can give a predictable refractive outcome after the IOP stabilizes.
References 1. Tanito M, Ohira A, Chihara E. Surgical outcome of combined trabeculotomy and cataract surgery. J Glaucoma 2001; 10:302–308 2. Cashwell LF, Martin CA. Axial length decrease accompanying successful glaucoma filtration surgery. Ophthalmology 1999; 106:2307–2311 3. Kook MS, Kim HB, Lee SU. Short-term effect of mitomycin-C augmented trabeculectomy on axial length and corneal astigmatism. J Cataract Refract Surg 2001; 27: 518–523
4. Brown SVL. Discussion of the article by Cashwell and Martin: Axial length decrease accompanying successful glaucoma filtration surgery. Ophthalmology 1999; 106: 2311 ¨ , Ates H, Andac¸ K, Deli B. Axial length ¨ retmen O 5. U changes accompanying successful nonpenetrating glaucoma filtration surgery. Ophthalmologica 2003; 217: 199–203 6. Dickens MA, Cashwell LF. Long-term effect of cataract extraction on the function of an established filtering bleb. Ophthalmic Surg Lasers 1996; 27:9–14 7. Byrne SF, Green RL. Ultrasound of the Eye and Orbit. St Louis, MO, Mosby Year Book, 1992; 79–80 8. Casson RJ, Riddell CE, Rahman R, et al. Long-term effect of cataract surgery on intraocular pressure after trabeculectomy; extracapsular extraction versus phacoemulsification. J Cataract Refract Surg 2002; 28:2159– 2164 9. Tong JT, Miller KM. Intraocular pressure change after sutureless phacoemulsification and foldable posterior chamber lens implantation. J Cataract Refract Surg 1998; 24:256–262 10. Derbolav A, Vass C, Menapace R, et al. Long-term effect of phacoemulsification on intraocular pressure after trabeculectomy. J Cataract Refract Surg 2002; 28:425–430 11. Manoj B, Chako D, Khan MY. Effect of extracapsular cataract extraction and phacoemulsification performed after trabeculectomy on intraocular pressure. J Cataract Refract Surg 2000; 26:75–78 12. Mietz H, Andresen A, Welsandt G, Krieglstein GK. Effect of cataract surgery on intraocular pressure in eyes with previous trabeculectomy. Graefes Arch Clin Exp Ophthalmol 2001; 239:763–769
J CATARACT REFRACT SURG—VOL 30, DECEMBER 2004
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