Downloaded from http://bjo.bmj.com/ on June 19, 2015 - Published by group.bmj.com
Editorial
Modern-day cataract surgery: can we match growing expectations? M Rana, S Shah Cataract surgery has evolved from the ancient technique of ‘couching’ with suboptimal results to femtosecond laserassisted phacoemulsification with excellent visual results. It is the most frequently performed surgery in the world.1 The recent advances in surgical techniques have increased the safety and efficacy of this procedure. There have also been improvements in the techniques to measure ocular biometry and methods to calculate intraocular lens (IOL) power resulting in high expectations for increasingly better outcomes from surgeons and patients. The accuracy of the refractive end point depends on the potential errors from a multitude of factors, which are involved in the calculation of the IOL power, aside from the surgical aspects themselves. These variables include the axial length, corneal power measurements, assumed corneal refractive index, lens position and anterior chamber depth.2 Although these factors are closely related to each other, and a change in one may affect the other, they have been assumed to be relatively independent factors for the purposes of the mathematical formulae used to perform IOL power calculations. Hence, there is potential for errors in these calculations. Various mathematical formulae have been created to calculate the desired IOL power. Initially, the main variables used were axial length and corneal power and formed the ‘thin lens or theoretical formulae’.3–6 The next generation of regression formulae gave somewhat better results than the first generation.7–8 In the late 1980s, the third-generation formulae (Hoffer Q, Holladay 1 and SRK/T) were introduced and became widely used, and considered the effective lens position (ELP) in their calculation.8–11 However, there continued to be a variation in results, at least partly, due to the actual ELP compared to the calculated ELP.12 Preussner,13 in 2002, developed a raytracing method to calculate IOL power, and more recently, Olsen further steered Birmingham and Midland Eye Centre, City Hospital, Birmingham, West Midlands, UK Correspondence to Professor Sunil Shah, Birmingham and Midland Eye Centre, City Hospital, Birmingham B18 7QH, UK; [email protected]
the ray-tracing methods by taking every surface of cornea and lens into consideration in predicting the IOL power,14 However, despite these improvements, results remain somewhat variable. An error of 100 μm difference in AL measurement produces a refractive outcome of 0.3 D from the desired value.2 15 Ultrasound used for the measurement of AL has a mediocre longitudinal resolution of 200 μm and an accuracy of 100–120 μm,15 respectively. The emergence of partial coherence laser interferometry (PCLI) and optical low coherence reflectometry (OLCR), both non-contact techniques for optical biometry, have created a revolution in technology. PCLI and OLCR have a much higher resolution (about one-tenth of ultrasound).15–17 Many studies comparing PCLI against conventional ultrasound confirmed significantly better outcomes.15–16 However, despite this increased accuracy, the visual results remain variable. Knox Cartwright18 reported on a large multicentre audit of 55 567 procedures. A visual outcome of 6/6 or better was only seen in 51% of eyes with no other ocular pathology. Aristodemou12 similarly looked at refractive outcomes in their cohort of 8108 patients using three different formulae, and optimised A constants. Outcomes were found to be within ±0.25 D in 40%, ±0.50 D in 75% and ±1.00 D in 95% of patients. Although this may be considered acceptable to some, this still means that 5% of patients would have greater than 1 D refractive error and, hence, when considering premium IOLs, this would be a group that one may need to consider laser fine tuning. Norrby19 suggested that the three main sources of postoperative refractive errors were: preoperative AL measurement, preoperative estimation of postoperative IOL position and postoperative refractive determination; these factors made up for 80% of all errors. Of these, the largest cause was the prediction of IOL position (35%). Olsen has also highlighted this in his review of IOL power calculation.2 As choosing the correct IOL power remains problematic, there has been increasing interest in intraoperative measurements to achieve accurate results. Strategies that have evolved include intraoperative optical refractive biometry
(Lanchulev20) and wavefront aberrometry by the Orange (WaveTec Vision, Aliso Viejo, California, USA) using the Talbot moiré interferometry21 or the open field Aston aberrometer.22 They have shown to have predictive refractive errors within 0.25 D in 80% of cases. Hirnschall23 previously had reported on measurement of postoperative anterior chamber depth (ACD) using anterior segment time domain optical coherence tomography (OCT). The best indicator of the ACD value was the anterior capsule position after implantation of a capsular tension ring. The same authors have taken their previous study further, by configuring an intraoperative measured ACD partial least square regression (PLSR) formula to calculate the postoperative refractive outcome, and have compared the results to using conventional multiple regression formulae.24 The PLSR formulae proved to be superior to all the other formulae and the weighting of explanatory variables was reduced. Although the direct comparison and statistical analysis did not show a significant difference between the PLSR formula and other individual third-generation regression formulae, it still had relatively high prediction rates. This is potentially a major leap towards the more accurate prediction of ACD, a factor which has been proven, time and time again, to be responsible for poor refractive outcomes. The future looks bright with the potential incorporation of all these new techniques into our routine cataract practice leading to more consistent and accurate results for our patients. Contributors Both authors have been involved in the concept and writing of this article. Competing interests None. Provenance and peer review Commissioned; internally peer reviewed.
To cite Rana M, Shah S. Br J Ophthalmol 2014;98:1313–1314. Published Online First 17 July 2014
▸ http://dx.doi.org/10.1136/bjophthalmol-2013304737
Br J Ophthalmol 2014;98:1313–1314. doi:10.1136/bjophthalmol-2014-304962
Rana M, et al. Br J Ophthalmol October 2014 Vol 98 No 10
1313
Downloaded from http://bjo.bmj.com/ on June 19, 2015 - Published by group.bmj.com
Editorial REFERENCES 1
2 3
4
5 6 7 8
9
10
1314
Apple DJ, Peng Q, Visessook N, et al. Surgical prevention of posterior capsule opacification. Part 1 (Progress in eliminating this complication of cataract surgery). J Cataract Refract Surg 2000;26:180–7. Olsen T. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 1992;18:125–9. Colenbrander MC. Calculation of the power of iris clip lens for distant vision. Br J Ophthalmol 1973;57:735–40. Fydorov SN, Galin MA, Linksz A. Calculation of optical power of intraocular lenses. Invest Ophthamol Vis Scie 1975;14:625–8. Binkhorst RD. The optical design of intraocular lens implants. Ophthalmic Surg 1975;6:17–31. Binkhorst RD. Intraocular lens power calculation. Int Ophthamol Clin 1979;19:237–52. Olsen T. Calculation of intraocular lens power: a review. Acta Ophthalmol Scand 2007;85:472–85. Haigis W. Matrix-optical representation of currently used intraocular lens power formulas. J Refract Surg 2009;25:229–34. Holladay JT, Prager TC, Chandler TY, et al. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 1988;14:17–24. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg 1990;16:333–40; correction, 528
11
12
13
14
15
16
17
18
Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg 1993;19:700–12; errata 1994;20:677. Aristodemou P, Knox Cartwright NE, Sparrow JM, et al. Formula choice: Hoffer Q, Holladay 1, or SRK/T and refractive outcomes in 8108 eyes after cataract surgery with biometry by partial coherence interferometry. J Cataract Refract Surg 2011;37:63–71. Preussner PR, Wahl J, Lahdo H, et al. Ray tracing for intraocular lens calculation. J Cataract Refract Surg 2002;28:1412–9. Olsen T, Croydon L, Gimbel H. Intraocular lens power calculation with an improved anterior chamber depth prediction algorithm. J Cataract Refract Surg 1995;21:313–9. Rajan MS, Keilhorn I, Bell JA. Partial coherence laser interferometry vs conventional ultrasound biometry in intraocular lens power calculations. Eye 2002;16:552–6. Findl O, Drexler W, Menapace R, et al. High precision biometry of pseudophakic eyes using partial coherence interferometry. J Cataract Refract Surg 1998;24:1087–93. Schmid GF. Axial and peripheral eye length measured with optical low coherence reflectometry. J Biomed Opt 2003;8:655–62. Knox Cartwright NE, Johnston RL, Jaycock PD, et al. The Cataract National Dataset electronic multicentre audit of 55 567 operations: when should IOLMaster
19 20
21
22
23
24
biometric measurements be rechecked. Eye (Lond) 2010;24:894–900. Norrby S. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 2008;34:368–76. Ianchulev T, Salz J, Hoffer K, et al. Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements. J Cataract Refract Surg 2005;31:1530–6. Chen M. Correlation between ORange (Gen 1, pseudophakic) intraoperative refraction and 1-week postcataract surgery autorefraction. Clin Ophthalmol 2011;5:197–9. http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC3045070/pdf/opth-5–197.pdfAccessed (15 Aug 2012). Bhatt UK, Sheppard AL, Shah S, et al. Design and validity of a miniaturized open-field aberrometer. J Cataract Refract Surg 2013;39:36–40. Hirnschall N, Amir-Asgari S, Maedel S, et al. Predicting the postoperative intraocular lens position using the continuous intraoperative optical coherence tomography. Invest Ophthalmol Vis Sci 2013;54:5196–203. Hirnschall N, Norrby S, Weber M, et al. Using continuous intraoperative optical coherence tomography measurements of the aphakic eye for intraocular lens power calculation. Br J Ophthalmol Published Online First: 11 Feb 2014. doi:10.1136/ bjophthalmol-2013-304731
Rana M, et al. Br J Ophthalmol October 2014 Vol 98 No 10
Downloaded from http://bjo.bmj.com/ on June 19, 2015 - Published by group.bmj.com
Modern-day cataract surgery: can we match growing expectations? M Rana and S Shah Br J Ophthalmol 2014 98: 1313-1314 originally published online July 17, 2014
doi: 10.1136/bjophthalmol-2014-304962 Updated information and services can be found at: http://bjo.bmj.com/content/98/10/1313
These include:
References Email alerting service
Topic Collections
This article cites 23 articles, 2 of which you can access for free at: http://bjo.bmj.com/content/98/10/1313#BIBL Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.
Articles on similar topics can be found in the following collections Optic nerve (664) Optics and refraction (472) Lens and zonules (760) Ophthalmologic surgical procedures (1130)
Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
Editorial
Modern-day cataract surgery: can we match growing expectations? M Rana, S Shah Cataract surgery has evolved from the ancient technique of ‘couching’ with suboptimal results to femtosecond laserassisted phacoemulsification with excellent visual results. It is the most frequently performed surgery in the world.1 The recent advances in surgical techniques have increased the safety and efficacy of this procedure. There have also been improvements in the techniques to measure ocular biometry and methods to calculate intraocular lens (IOL) power resulting in high expectations for increasingly better outcomes from surgeons and patients. The accuracy of the refractive end point depends on the potential errors from a multitude of factors, which are involved in the calculation of the IOL power, aside from the surgical aspects themselves. These variables include the axial length, corneal power measurements, assumed corneal refractive index, lens position and anterior chamber depth.2 Although these factors are closely related to each other, and a change in one may affect the other, they have been assumed to be relatively independent factors for the purposes of the mathematical formulae used to perform IOL power calculations. Hence, there is potential for errors in these calculations. Various mathematical formulae have been created to calculate the desired IOL power. Initially, the main variables used were axial length and corneal power and formed the ‘thin lens or theoretical formulae’.3–6 The next generation of regression formulae gave somewhat better results than the first generation.7–8 In the late 1980s, the third-generation formulae (Hoffer Q, Holladay 1 and SRK/T) were introduced and became widely used, and considered the effective lens position (ELP) in their calculation.8–11 However, there continued to be a variation in results, at least partly, due to the actual ELP compared to the calculated ELP.12 Preussner,13 in 2002, developed a raytracing method to calculate IOL power, and more recently, Olsen further steered Birmingham and Midland Eye Centre, City Hospital, Birmingham, West Midlands, UK Correspondence to Professor Sunil Shah, Birmingham and Midland Eye Centre, City Hospital, Birmingham B18 7QH, UK; [email protected]
the ray-tracing methods by taking every surface of cornea and lens into consideration in predicting the IOL power,14 However, despite these improvements, results remain somewhat variable. An error of 100 μm difference in AL measurement produces a refractive outcome of 0.3 D from the desired value.2 15 Ultrasound used for the measurement of AL has a mediocre longitudinal resolution of 200 μm and an accuracy of 100–120 μm,15 respectively. The emergence of partial coherence laser interferometry (PCLI) and optical low coherence reflectometry (OLCR), both non-contact techniques for optical biometry, have created a revolution in technology. PCLI and OLCR have a much higher resolution (about one-tenth of ultrasound).15–17 Many studies comparing PCLI against conventional ultrasound confirmed significantly better outcomes.15–16 However, despite this increased accuracy, the visual results remain variable. Knox Cartwright18 reported on a large multicentre audit of 55 567 procedures. A visual outcome of 6/6 or better was only seen in 51% of eyes with no other ocular pathology. Aristodemou12 similarly looked at refractive outcomes in their cohort of 8108 patients using three different formulae, and optimised A constants. Outcomes were found to be within ±0.25 D in 40%, ±0.50 D in 75% and ±1.00 D in 95% of patients. Although this may be considered acceptable to some, this still means that 5% of patients would have greater than 1 D refractive error and, hence, when considering premium IOLs, this would be a group that one may need to consider laser fine tuning. Norrby19 suggested that the three main sources of postoperative refractive errors were: preoperative AL measurement, preoperative estimation of postoperative IOL position and postoperative refractive determination; these factors made up for 80% of all errors. Of these, the largest cause was the prediction of IOL position (35%). Olsen has also highlighted this in his review of IOL power calculation.2 As choosing the correct IOL power remains problematic, there has been increasing interest in intraoperative measurements to achieve accurate results. Strategies that have evolved include intraoperative optical refractive biometry
(Lanchulev20) and wavefront aberrometry by the Orange (WaveTec Vision, Aliso Viejo, California, USA) using the Talbot moiré interferometry21 or the open field Aston aberrometer.22 They have shown to have predictive refractive errors within 0.25 D in 80% of cases. Hirnschall23 previously had reported on measurement of postoperative anterior chamber depth (ACD) using anterior segment time domain optical coherence tomography (OCT). The best indicator of the ACD value was the anterior capsule position after implantation of a capsular tension ring. The same authors have taken their previous study further, by configuring an intraoperative measured ACD partial least square regression (PLSR) formula to calculate the postoperative refractive outcome, and have compared the results to using conventional multiple regression formulae.24 The PLSR formulae proved to be superior to all the other formulae and the weighting of explanatory variables was reduced. Although the direct comparison and statistical analysis did not show a significant difference between the PLSR formula and other individual third-generation regression formulae, it still had relatively high prediction rates. This is potentially a major leap towards the more accurate prediction of ACD, a factor which has been proven, time and time again, to be responsible for poor refractive outcomes. The future looks bright with the potential incorporation of all these new techniques into our routine cataract practice leading to more consistent and accurate results for our patients. Contributors Both authors have been involved in the concept and writing of this article. Competing interests None. Provenance and peer review Commissioned; internally peer reviewed.
To cite Rana M, Shah S. Br J Ophthalmol 2014;98:1313–1314. Published Online First 17 July 2014
▸ http://dx.doi.org/10.1136/bjophthalmol-2013304737
Br J Ophthalmol 2014;98:1313–1314. doi:10.1136/bjophthalmol-2014-304962
Rana M, et al. Br J Ophthalmol October 2014 Vol 98 No 10
1313
Downloaded from http://bjo.bmj.com/ on June 19, 2015 - Published by group.bmj.com
Editorial REFERENCES 1
2 3
4
5 6 7 8
9
10
1314
Apple DJ, Peng Q, Visessook N, et al. Surgical prevention of posterior capsule opacification. Part 1 (Progress in eliminating this complication of cataract surgery). J Cataract Refract Surg 2000;26:180–7. Olsen T. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 1992;18:125–9. Colenbrander MC. Calculation of the power of iris clip lens for distant vision. Br J Ophthalmol 1973;57:735–40. Fydorov SN, Galin MA, Linksz A. Calculation of optical power of intraocular lenses. Invest Ophthamol Vis Scie 1975;14:625–8. Binkhorst RD. The optical design of intraocular lens implants. Ophthalmic Surg 1975;6:17–31. Binkhorst RD. Intraocular lens power calculation. Int Ophthamol Clin 1979;19:237–52. Olsen T. Calculation of intraocular lens power: a review. Acta Ophthalmol Scand 2007;85:472–85. Haigis W. Matrix-optical representation of currently used intraocular lens power formulas. J Refract Surg 2009;25:229–34. Holladay JT, Prager TC, Chandler TY, et al. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 1988;14:17–24. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg 1990;16:333–40; correction, 528
11
12
13
14
15
16
17
18
Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg 1993;19:700–12; errata 1994;20:677. Aristodemou P, Knox Cartwright NE, Sparrow JM, et al. Formula choice: Hoffer Q, Holladay 1, or SRK/T and refractive outcomes in 8108 eyes after cataract surgery with biometry by partial coherence interferometry. J Cataract Refract Surg 2011;37:63–71. Preussner PR, Wahl J, Lahdo H, et al. Ray tracing for intraocular lens calculation. J Cataract Refract Surg 2002;28:1412–9. Olsen T, Croydon L, Gimbel H. Intraocular lens power calculation with an improved anterior chamber depth prediction algorithm. J Cataract Refract Surg 1995;21:313–9. Rajan MS, Keilhorn I, Bell JA. Partial coherence laser interferometry vs conventional ultrasound biometry in intraocular lens power calculations. Eye 2002;16:552–6. Findl O, Drexler W, Menapace R, et al. High precision biometry of pseudophakic eyes using partial coherence interferometry. J Cataract Refract Surg 1998;24:1087–93. Schmid GF. Axial and peripheral eye length measured with optical low coherence reflectometry. J Biomed Opt 2003;8:655–62. Knox Cartwright NE, Johnston RL, Jaycock PD, et al. The Cataract National Dataset electronic multicentre audit of 55 567 operations: when should IOLMaster
19 20
21
22
23
24
biometric measurements be rechecked. Eye (Lond) 2010;24:894–900. Norrby S. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 2008;34:368–76. Ianchulev T, Salz J, Hoffer K, et al. Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements. J Cataract Refract Surg 2005;31:1530–6. Chen M. Correlation between ORange (Gen 1, pseudophakic) intraoperative refraction and 1-week postcataract surgery autorefraction. Clin Ophthalmol 2011;5:197–9. http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC3045070/pdf/opth-5–197.pdfAccessed (15 Aug 2012). Bhatt UK, Sheppard AL, Shah S, et al. Design and validity of a miniaturized open-field aberrometer. J Cataract Refract Surg 2013;39:36–40. Hirnschall N, Amir-Asgari S, Maedel S, et al. Predicting the postoperative intraocular lens position using the continuous intraoperative optical coherence tomography. Invest Ophthalmol Vis Sci 2013;54:5196–203. Hirnschall N, Norrby S, Weber M, et al. Using continuous intraoperative optical coherence tomography measurements of the aphakic eye for intraocular lens power calculation. Br J Ophthalmol Published Online First: 11 Feb 2014. doi:10.1136/ bjophthalmol-2013-304731
Rana M, et al. Br J Ophthalmol October 2014 Vol 98 No 10
Downloaded from http://bjo.bmj.com/ on June 19, 2015 - Published by group.bmj.com
Modern-day cataract surgery: can we match growing expectations? M Rana and S Shah Br J Ophthalmol 2014 98: 1313-1314 originally published online July 17, 2014
doi: 10.1136/bjophthalmol-2014-304962 Updated information and services can be found at: http://bjo.bmj.com/content/98/10/1313
These include:
References Email alerting service
Topic Collections
This article cites 23 articles, 2 of which you can access for free at: http://bjo.bmj.com/content/98/10/1313#BIBL Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.
Articles on similar topics can be found in the following collections Optic nerve (664) Optics and refraction (472) Lens and zonules (760) Ophthalmologic surgical procedures (1130)
Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
