1998 European cataract outcome study

articles

1998 European Cataract Outcome Study Report from the European Cataract Outcome Study Group Mats Lundstro¨m, MD, Peter Barry, MD, Eugenio Leite, MD, Helen Seward, MD, Ulf Stenevi, MD ABSTRACT Purpose: To collect clinical data on cataract surgery to allow participating surgeons to compare their performance with that of their colleagues in an anonymous manner. Setting: Surgeons from 31 surgical units providing cataract surgery in 13 European countries. Methods: Every patient at each participating unit having surgery during 1 study month was evaluated. Data were reported to the coordinating center at the time of surgery and at the final examination. When the study was closed 6 months after surgery, all participants were provided with the outcomes from their own patients so they could compare them with outcomes from other centers. Results: The study included preoperative and intraoperative data on 2950 patients. Complete follow-up data were available for 2731 patients. The surgical audit included surgically induced astigmatism, proximity of target refraction, and the frequency of major complications. For each variable, a large variation in outcome between participating centers was found. Most centers had results both above and below average for different variables. Conclusion: Cataract surgery data collected from 31 units in 13 European countries allowed participants to compare their performance with that of their colleagues in an anonymous manner. Significant variation was found in the outcomes among the units, with many units reporting results above and below the averages. J Cataract Refract Surg 2001; 27:1176 –1184 © 2001 ASCRS and ESCRS

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any national surveys and multicenter studies have focused on the outcomes of routine cataract surgery.1– 4 Their purposes include evaluating the relationship between the annual volume of cataract procedures and preferred practice,1 the outcomes of cataract surAccepted for publication November 24, 2000. Reprint requests to Mats Lundstro¨m, MD, PhD, Department of Ophthalmology, Blekinge Hospital, S-371 85 Karlskrona, Sweden. © 2001 ASCRS and ESCRS Published by Elsevier Science Inc.

gery,2 and the quality of cataract surgery performance in daily practice. Others sought to improve the quality of care,3 compare outcomes from hospitals and smaller clinics,4 or evaluate waiting time and priority setting.5 These studies have a common design; that is, they are observational with a case series (consecutive cases). This design is used because case series studies show the performance of routine care of cataract patients better than randomized clinical trials. Patients are selected for a 0886-3350/01/$–see front matter PII S0886-3350(01)00772-6

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case series in several ways including by time (ie, consecutive cataract extractions at participating units during a specific period such as 1 week3 or 1 month2) and by number (ie, consecutive patients from participating units1). Some outcomes, such as postoperative visual acuity in the operated eye, are similar among studies. In contrast, international multicenter studies of cataract surgery outcomes report large differences in surgical technique among units.6 The European Cataract Outcome Study Group has performed multicenter studies of cataract surgery outcomes since 1995 (unpublished data). In these studies, every patient at each participating unit having surgery during 1 study month was analyzed. Clinical data collected for the surgeons’ benefit were postoperative visual acuity, surgically induced astigmatism (SIA), proximity of target refraction, and frequency of major complications such as vitreous loss and torn capsule. Each participant received the outcomes from his or her patients and could compare them with those from other units in an anonymous manner. Participants could, for example, identify the precision of biometry in Clinic A, the absence of surgical complications in Clinic B, and the minimal SIA in Clinic C and use these targets to improve their own performance. Demographic data collected to benefit health managers and health providers were patient age, sex, time on waiting list, first- or second-eye cataract surgery, type of anesthesia, and whether surgery was performed on an inpatient or outpatient basis. Data collected of interest to the industry, surgeons, and health managers were the frequency of phacoemulsification versus standard extracapsular cataract extraction (ECCE) and the type of intraocular lens (IOL) implanted (ie, foldable or nonfoldable). This report describes the technique and organization used for the European Cataract Outcome Study and the results of the 1998 study.

Patients and Methods The 3 aims of the study were to (1) evaluate the variation in cataract surgery outcomes among participating units to allow surgeons to anonymously compare their performance with that of colleagues, stimulating clinical improvement; (2) study the variation in demo-

graphic data and techniques; (3) simplify data collection, minimizing the resources needed to participate in the study. According to the protocol of the European Cataract Outcome Study Group, participating units were recruited by invitation during the 1995 Congress of the European Society of Cataract & Refractive Surgeons. Criteria for inclusion were an interest in clinical improvement in cataract surgery and performance of at least 200 cataract operations annually. This study included all consecutive patients having cataract extraction during October 1998 at the participating units. At the time of surgery, participants reported each cataract extraction to the coordinating center using a form (form 1). After the final postoperative examination and refraction were performed, several outcome variables were reported on a second form (form 2). The end point of the study was 6 months after surgery. Thus, follow-up data were collected at different times between 1 and 6 months. The length of follow-up (in days) in each case was noted. A manual described how each variable should be measured and reported. The following variables were reported at the time of surgery: unit number; patient number, age, and sex; date on waiting list; previous cataract extraction; visual acuity in the surgical and fellow eye; date of surgery; preexisting ocular pathology; type of surgery; type of IOL; target refraction; type of anesthesia; inpatient or outpatient surgery; and complications during surgery. The following variables were reported at the time of follow-up: unit number, patient number, preoperative and postoperative K-values in the surgical eye, the date of the final examination, visual acuity and refraction in the surgical eye, ocular comorbidity, and disposal of patient (eg, follow-up completed, cooperative or not, alive or deceased). All data collected from the units were transferred to a database at the coordinating center. At the end of the study, each participating unit received its average results as well as those of all patients included in the study. Each participant also received bar charts with the results of all participating units. The names of the units did not appear on the bar charts; that is, each unit had access to its own data and could anonymously compare its results with those of all other units. This approach was meant to permit a genuine audit and honest reporting and to

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Table 1. Origin of reporting units and number of reported cataract extractions per unit.

Country

Number of Units

Number of Patients

Total Patients

Czech Republic

3

266, 272, 84

622

Denmark

4

18, 107, 47, 18

190

France

3

89, 163, 19

271

Germany

1

138

138

Holland

4

21, 52, 45, 137

255

Ireland

1

33

33

Israel

1

40

40

Italy

2

30, 27

57

Norway

2

128, 321

445

Portugal

1

105

105

Sweden

4

80, 162, 101, 183

526 202

United Kingdom

4

105, 48, 11, 38

Yugoslavia

1

47

47

identify benchmarks based on data from the different centers. The methods used to describe astigmatism and refraction after surgery are outlined in Appendix A. Statistical Analysis Statistical analyses were done using SPSS version 8.0. The relationships between categorical data were tested by a chi-square or logistic regression and bivariate correlation using the Pearson correlation coefficient.

Results Thirty-one units from 13 countries participated in the study, and preoperative and intraoperative data were

available for 2950 cataract extractions. The number of operations reported from each unit was between 11 and 321 (mean 95; median 80). Table 1 shows the reporting units and the number of operations. In some cases, the reporting unit was a single surgeon and in other cases, several surgeons. Outcome data from form 2 were available for 2731 patients, representing 92.6% of the original number of patients having surgery. Two surgeons reported no follow-up patients. The other participants reported between 41.1% and 100% (mean 96.2%; median 100%). Outcomes of Surgery Figure 1 shows the complications during surgery and the number of reported operations performed at each unit. Intraoperative complications occurred in 3.5% of all cases and included posterior capsule rupture (2.2%), vitreous loss (1.5%), and dropped nucleus (0.2%). The mean complication rate in the 13 units with more than 100 reported cataract extractions was 3.6%. Ten of the 2731 patients with data reported on form 2 died during the follow-up. Twenty-six patients were unable to complete the follow-up, and 369 required follow-up longer than 6 months because of ongoing problems after surgery or a final examination later than 6 months after surgery. The postoperative results are based on 2326 patients (85.2% of the reported cases and 78.8% of patients having surgery in October 1998 at the participating units). Coexisting eye disease was present in 37.5% of cases. Preoperative visual acuity in the surgical eye was 0.1 or worse in 31.5% of all cases and in the nonsurgical eye, worse than 0.5 in 35.6%. There was a large variation

Figure 1. (Lundstro¨m) Complications during surgery by percentage of operations performed. Each bar represents 1 unit. The number of surgeries reported by a unit is marked as a bar with a negative value (below the x-axis) (–1 ⫽ ⬍40 operations, –2 ⫽ 40 to 100; –3 ⫽ ⬎100). Posterior capsule rupture marked with bold limits means unit had 1 dropped nucleus.

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in the mean values of all variables among participating units (Table 2), showing that the case mix differed among the units. A postoperative visual acuity of 0.5 or better was achieved in 85.4% of all cases. A postoperative acuity of 0.5 or better was achieved in 93.5% of patients without known preoperative ocular comorbidity, in 72.1% with ocular comorbidity, in 64.4% with age-related macular degeneration (ARMD), and in 76.4% with glaucoma in the surgical eye. The mean visual acuity after surgery in the surgical eyes (percentage of patients achieving 0.5 or better) is shown by unit in Figure 2. The difference between the target refraction and the spherical equivalent, which was calculated for each patient, is shown in Figure 3; each surgical unit is represented by a box. The surgical units in the figure are sorted by their mean difference. On average, the difference was 0.71 diopter (D) (range 0.41 to 1.12 D). In 77.7% of all cases (range among units 56.0% to 92.9%), the final refraction was less than 1.00 D from the target refraction. Figure 3 also shows the spread of values for each unit and the eventual skewed distribution. The mean target refraction was – 0.27 D (range – 0.90 to 0.03 D). Table 3 shows the postoperative astigmatism and induced astigmatism. All astigmatism values refer to cor-

Figure 2. (Lundstro¨m) Mean visual acuity after surgery. The bars indicate the percentage of patients who achieved a postoperative visual acuity of 0.5 or better in the surgical eye. Each bar represents 1 unit. The mean for all patients was 85.4% and for all units, 85.2%.

neal astigmatism calculated using K-values. The mean postoperative astigmatism in all patients was 1.10 D. The mean induced astigmatism in each patient was calculated using the subtraction, algebraic, or Naeser polar value7 method. The mean values for all study patients using the 3 methods were 0.60 D, 0.94 D, and 0.77 D, respectively. The induced astigmatism (Naeser polar values) for all units is shown in Figure 4. The units are sorted by their average value (mean value). Figure 4 also shows the spread of values and eventual skewed distribution of values for each surgical unit.

Table 2. Preoperative visual acuity and coexisting disease in the eye to have surgery. All Patients Parameter

All Units

Mean

Mean

Minimum

Maximum

SD

Ocular comorbidity, surgical eye (%)

37.5

37.9

15.2

61.1

11.4

VA ⱕ0.1, surgical eye (%)

31.5

32.7

5.8

73.3

14.7

VA ⬍0.5, nonsurgical eye (%)

35.6

34.6

13.4

66.7

13.7

VA ⫽ visual acuity

Table 3. Postoperative and induced astigmatism. All Patients Parameter

All Units

Mean

Mean

Minimum

Maximum

SD

1.10

1.11

0.49

1.89

0.27

Subtraction

0.60

0.63

0.28

1.29

0.24

Naeser

0.77

0.79

0.31

1.43

0.27

Algebraic

0.94

0.99

0.36

1.77

0.33

Postoperative astigmatism (D) Induced astigmatism (D)

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Figure 3. (Lundstro¨m) The difference between the target refraction

Figure 4. (Lundstro¨m) Induced astigmatism (diopters) calculated

and final refraction for 28 units. The final refraction is shown as a spherical equivalent. The units are sorted by their mean difference. Each box represents 1 unit. Within the box is the middle 50% of the values, with the dark line representing the median of the distribution. The vertical lines above and under the box indicate the extent of 95% of the values. The mean for all patients was 0.71 D. The range among units was 0.41 to 1.12 D.

as Naeser polar values in 26 units. The units are sorted by mean induced astigmatism. Each box represents 1 unit. Within the box is the middle 50% of the values, with the dark line representing the median of the distribution. The vertical lines above and under the box indicate the extent of 95% of the values.

Demography and Monitoring of Cataract Surgery Table 4 shows the demographic data of the 2950 reported cataract extractions. The mean age of the patients was 73.7 years, and 65.7% were women. Secondeye surgery was performed in 41.5% of patients. Table 5 shows the distribution of mean waiting times (time from listing for surgery to date of surgery), type of anesthesia, and whether the surgery was inpatient or outpatient. Phacoemulsification was the most common procedure (94.8%), and a foldable IOL was implanted in 50.5% of cases. Table 6 shows the type of surgery and IOL. Table 7 shows the correlation between performance, preoperative data, and outcome data. A comparison of the mean values in each unit showed a correlation between preoperative comorbidity in the surgical eye and visual outcome (P ⫽ .001) and between the use of a foldable IOL (ie, small incision surgery) and induced astigmatism (P ⫽ .018). There was also a correlation between general anesthesia and inpatient surgery (P ⫽ .002). There were no correlations between any variable and the country (ie, origin of unit) or surgical volume. Table 8 shows the relationship between performance or preoperative conditions and outcome. There

was a strong relationship between complications during surgery and visual outcome and between a known preoperative ocular comorbidity and visual outcome. There was also a relationship between inpatient surgery and a poor visual outcome but no relationship between general anesthesia and visual outcome. Logistic regression analysis showed preoperative ocular morbidity in the surgical eye was most strongly related to poor outcome. The outcome was strongly related (P ⬍ .001, chisquare) to all postoperatively known coexisting eye diseases (glaucoma, ARMD, diabetic retinopathy or other diseases). The mean frequency of ARMD postoperatively was 13.7% (range among units 3.1% to 29.7%) and of glaucoma, 8.4% (range among units 0% to 20.8%).

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Table 4. Demographic data. All Patients Parameter

Mean

All Units Mean Minimum Maximum SD

Age (years)

73.7

73.2

55.9

79.3

4.2

Women (%)

65.7

63.7

45.0

72.5

6.2

Second-eye surgery (%)

41.5

40.2

16.7

77.1

11.8

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Table 5. Process data. All Patients Parameter

All Units

Mean

Mean

Median

Minimum

Maximum

SD

5.6

5.6

5.8

1.1

18.1

3.8

60.4

12.3

Waiting time (months) Anesthesia (%) General

4.0

6.2

1.4

0

Retrobulbar/peribulbar

41.6

52.6

60.0

0

100

38.7

Drops

43.6

32.1

0

0

100

41.8

8.5

6.8

0

0

28.5

27.6

10.4

0

Sub-Tenon’s Inpatient surgery (%)

57.6

16.8

100

36

Table 6. Percentage of phacoemulsification procedures and foldable IOLs implanted. All Patients

All Units

Parameter

Mean

Mean

Median

Minimum

Maximum

SD

Phaco (%)

94.8

92.4

97.9

7.5

100

17.6

Foldable IOL (%)

50.5

46.8

44.8

0

100

37.2

Phaco ⫽ phacoemulsification; IOL ⫽ intraocular lens

Table 7. Correlation between performance, preoperative data, and outcome. Variable

Level

r

P Value

Comorbidity in surgical and postop visual acuity ⱖ0.5

U

⫺0.609

.001

Best corrected preop visual acuity, better eye and postop visual acuity, surgical eye

I

0.288

⬍.001

Inpatient surgery and general anesthesia

U

0.535

.002

Postop astigmatism and induced astigmatism, algebraic method

U

0.789

⬍.001

Percentage foldable lenses and induced astigmatism, algebraic method

U

⫺0.460

.018

r ⫽ correlation coefficient; U ⫽ unit; I ⫽ individual

Table 8. Relationship between performance and outcome; all variables tested together (logistic regression) against outcome. P Value Chi Square

Variable Type of anesthesia (local or general) versus postop visual acuity ⱖ0.5 Inpatient surgery versus postop visual acuity ⱖ0.5 Surgical complication versus postop visual acuity ⱖ0.5 Ocular comorbidity versus postop visual acuity ⱖ0.5

Data Feedback to Participants Each participant received bar charts with results from all units for variables within 3 areas: (1) surgeon’s benefit (intraoperative complications, postoperative visual acuity, difference between planned and final refrac-

Logistic Regression, All Variables

.054

.7828

⬍.001

.0012

.001

.0016

⬍.001

⬍.001

tion, induced astigmatism, and ocular comorbidity); (2) monitoring (waiting time, preoperative visual acuity, anesthesia, inpatient or outpatient surgery, and secondeye surgery); (3) technical procedure (frequency of phacoemulsification and foldable IOL implantation).

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Discussion One purpose of this study was to explore the differences in techniques and outcomes in routine cataract surgery at participating units. The average patient in this study was a woman aged 73 having first-eye surgery who had no ocular comorbidity. The median preoperative visual acuity was 0.3 in the surgical eye and 0.6 in the fellow eye. In 31.5% of all patients, the acuity in the surgical eye was 0.1 or less (range among units 5.8% to 73.3%), indicating a large variation in preoperative visual function. The median preoperative visual acuity in the surgical eye is comparable to that reported in studies from the United States1,8 and better than that reported in European studies.8,9 The large variation in preoperative visual acuity among units is interesting considering the outcomes. Other observational studies found a relationship between poor preoperative visual acuity and a poor visual outcome.10 We also found a correlation between best corrected visual acuity before surgery and the visual outcome after surgery (P ⬍ .001). The reported visual outcome in our study was good. Postoperatively, 85.4% of all cases achieved a visual acuity of 0.5 or better, similar to the 87.1% rate reported by Wegener and coauthors.4 In patients without known preoperative ocular comorbidity, the postoperative visual acuity was 0.5 or better in 93.5%, similar to the 93% rate reported by Schein et al.1 in patients having first-eye surgery and the 92% rate reported by Desai and coauthors.11 Of our patients with known ocular comorbidity, 72.1% achieved an acuity of 0.5 or better, similar to the 77% rate reported by Desai and coauthors.11 An important finding in our study was the poor outcomes in patients with ARMD and the large variation among units in the frequency of ARMD. It is important to identify the magnitude of this variable when comparing the outcomes of different providers of cataract surgery. In 77.7% of all cases (range among units 56.0% to 92.9%), the final refraction (spherical equivalent) was within ⫾1.00 D of the target refraction. Høvding and coauthors12 report a rate of 67% in a hospital practice and Hoffmann and coauthors,13 a rate of 83%. One weakness of our study was the lack of information on which IOL power calculation formulas were used. In our study, there was considerable spread in the values for the difference between the final and target 1182

refractions in many of the units. In many units, a number of patients also had a large difference between the target refraction and final refraction, resulting in a skewed distribution. Foldable IOLs were used in 50.5% of all cases. On the level of units, the frequency of foldable lenses correlated with the average induced astigmatism (algebraic method, P ⫽ .018, Pearson correlation coefficient). The frequency of foldable IOL use was higher than that in earlier studies by the European Cataract Outcome Study Group. In the 1997 study, the frequency was 26.7% (unpublished data). Other studies have shown that phacoemulsification results in less SIA than ECCE with a large incision.14 It has also been shown that small incision surgery with implantation of a foldable IOL results in lower induced astigmatism than surgery with a larger incision and implantation of a rigid lens.15,16 Our results also indicate that in routine cataract surgery, lower induced astigmatism is achieved within 6 months postoperatively after small incision surgery than after large incision surgery. Furthermore, a simplified data collection form with K-values and IOL type seems sufficient for establishing SIA benchmarks. With a longer follow-up, additional information on SIA can be obtained.17 Another goal of our study was to identify systematic reasons for poor outcomes. In some units, however, the number of reported cases was so small that the frequency of complications could not be interpreted. When the number of reported cases is too small, findings of a high frequency of complications or of no complications are inconclusive for statistical purposes. In the total cohort, however, the frequency of intraoperative complications was reasonably low. In our study, the rate of posterior capsule rupture was 2.2%; Schein et al.1 report a rate of 1.95% and Wegener and coauthors,4 of 5.2%. Vitreous loss rates were 1.5%, 1.39%, and 2.3%, respectively. Postoperative complications were not recorded in our study. The difference among units in the type of anesthesia used was significant. In a multinational study, Norregaard et al.6 report a frequency of retrobulbar anesthesia use between 31% and 70%. In our study, there was no correlation between the type of anesthesia and outcomes (postoperative visual acuity). There was also a significant difference in the frequency of inpatient surgery, with a range among units of 0% to 100%. There was a relationship between inpa-

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tient surgery and a poor visual outcome (ie, postoperative visual acuity ⬍0.5 in the surgical eye) (P ⬍ .001, chi-square test). In contrast, Holland et al.18 found no relationship between inpatient surgery and visual outcomes. The difference between our findings and those of Holland et al. may be because at many units today, inpatient surgery is used only in cases with complications during surgery or in patients with an ocular comorbidity or other systemic disease. A large variation was found among the participating units in almost all variables. When interpreting this finding, it must be remembered that the variables were of a different nature. For example, the difference among units in variables describing a process (eg, inpatient surgery, general anesthesia) was probably the result of established routines. Nine of 31 units contributed fewer than 40 cases. Thus, their results may not be statistically useful in a comparison among units and may therefore have biased the outcome. The reason for including these results in some analyses was to give participants the opportunity to compare their performance with that of their colleagues and thereby stimulate clinical improvement. In the analysis of astigmatism, however, 5 units were excluded because of too few cases. The results of our study served as a benchmark for the participating units. The impact on the participating units is not easily estimated. After the study, participants were asked whether they were influenced by the comparison of their results with those of others. Most judged the influence to be considerable in terms of improvement of results and change in technique.

References 1. Schein OD, Steinberg EP, Javitt JC, et al. Variation in cataract surgery practice and clinical outcomes. Ophthalmology 1994; 101:1142–1152 2. Desai P. The National Cataract Surgery Survey: II. Clinical outcomes. Eye 1993; 7:489 – 494 3. Stenevi U, Lundstro¨m M, Thorburn W. An outcome study of cataract surgery based on a national register. Acta Ophthalmol Scand 1997; 75:688 – 691 4. Wegener M, Alsbirk PH, Højgaard-Olsen K. Outcome of 1000 consecutive clinic- and hospital-based cataract surgeries in a Danish county. J Cataract Refract Surg 1998; 24:1152–1160 5. Lundstro¨m M, Stenevi U, Thorburn W. Assessment of waiting time and priority setting by means of a national register. Int J Technol Assess Health Care 1996; 12:136 –140

6. Norregaard JC, Schein OD, Bellan L, et al. International variation in anesthesia care during cataract surgery; results from the International Cataract Surgery Outcomes Study. Arch Ophthalmol 1997; 115:1304 –1308 7. Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 1990; 16:741–745 8. Norregaard JC, Bernth-Petersen P, Alonso J, et al. Variation in indications for cataract surgery in the United States, Denmark, Canada, and Spain: results from the International Cataract Surgery Outcomes Study. Br J Ophthalmol 1998; 82:1107–1111 9. Courtney P. The National Cataract Surgery Survey: I. Method and descriptive features. Eye 1992; 6:487– 492 10. Norregarrd JC, Hindsberger C, Alonso J, et al. Visual outcomes of cataract surgery in the United States, Canada, Denmark, and Spain: report from the International Cataract Surgery Outcomes Study. Arch Ophthalmol 1998; 116:1095–1100 11. 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 –1340 12. Høvding G, Natvik C, Sletteberg O. The refractive error after implantation of a posterior chamber intraocular lens; the accuracy of IOL power calculation in a hospital practice. Acta Ophthalmol 1994; 72:612– 616 13. Hoffmann PC, Hu¨tz WW, Eckhardt HB. Bedeutung der Formelauswahl fu¨r die postoperative Refraktion nach Katarakt-Operation. Klin Monatsbl Augenheilkd 1997; 211:168 –177 14. Olsen T, Bargum R. Outcome monitoring in cataract surgery. Acta Ophthalmol Scand 1995; 73:433– 437 15. Masket S. Horizontal anchor suture closure method for small incision cataract surgery. J Cataract Refract Surg 1991; 17:689 – 695 16. Oshika T, Tsuboi S, Yaguchi S, et al. Comparative study of intraocular lens implantation through 3.2- and 5.5-mm incisions. Ophthalmology 1994; 101:1183–1190 17. Rainer G, Menapace R, Vass C, et al. Surgically induced astigmatism following a 4.0 mm sclerocorneal valve incision. J Cataract Refract Surg 1997; 23:358 –364 18. Holland GN, Earl DT, Wheeler NC, et al. Results of inpatient and outpatient cataract surgery; a historical cohort comparison. Ophthalmology 1992; 99:845– 852

From the Departments of Ophthalmology, Blekinge Hospital, Karlskrona, Sweden (Lundstro¨m), University Hospital of Coimbra, Coimbra, Portugal (Leite), and Sahlgren’s University Hospital, Mo¨lndal, Sweden (Stenevi); The Eye Clinic, Dublin, Ireland (Barry); Croydon Eye Unit, Surrey, United Kingdom (Seward). Presented at the XVIIth Congress of the European Society of Cataract & Refractive Surgeons, Vienna, Austria, September 1999. Supported by the County of Blekinge, The National Board of Health and Welfare, Sweden, and Pharmacia.

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Appendix A

Appendix B

Methods Used to Describe the Results of Surgery Postoperative Astigmatism Absolute value of the difference between postoperative Kvalues. Induced Astigmatism Analyzed using the following methods as described by DamJohansen and coauthors1: All astigmatism are regarded as being a cylinder with a minimum refractive power (zero) in the meridian a and a maximum refractive power (K) in the meridian (a ⫹ 90°). K1 ⫽ preoperative astigmatism; K3 ⫽ postoperative astigmatism; a1 ⫽ preoperative axis; a3 ⫽ postoperative axis; K2 ⫽ induced astigmatism. Subtraction method: K2 ⫽ K3 – K1. The calculated mean values are taken from absolute values. Naeser2 polar value: K2 ⫽ K3 ⫻ cos(2 ⫻ a3) – K1 ⫻ cos(2 ⫻ a1). The calculated mean values are taken from absolute values. Algebraic method: Conditions: a) If 45° ⬍ a1 ⬍ 135°. Then is K1 is multiplied with –1. b) If 45° ⬍ a3 ⬍ 135°. Then is K3 is multiplied with –1. K2 ⫽ K3 – K1

Difference Between Intended Refraction and Final Refraction Intended refraction: From the biometry printout and chosen power of IOL. Final refraction: From the spherical equivalent of final refraction at follow-up. All differences calculated as absolute values whether the difference was in the myopic or hyperopic direction.

References 1. Dam-Johansen M, Olsen T, Theodorsen F. The longterm course of the surgically-induced astigmatism after a scleral tunnel incision. Eur J Implant Refract Surg 1994; 6:337–343 2. Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 1990; 16:741–745

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Participating Surgeons, Clinical Personnel, and Centers Guy Aflalo, MD, Service Ophtalmologie, Centre Hospitalier E. Bonnet, Frejus Cedex, France; David Allen, FRCOphth, Christopher Wood, MD, The Eye Infirmary, Sunderland, United Kingdom; Peter Barry, FRCS, FROphth, The Eye Clinic, St. Vincent’s University Hospital, Dublin, ¨ reIreland; Bengt Bergeå, MD, Eye Clinic, La¨kargruppen, O bro, Sweden; Michael Blumenthal, MD, Ein Tal Eye Center, Tel Aviv, Israel; Henrik Bom Olesen, MD, Eye Department, Holbaek Central Hospital, Holbaek, Denmark; Martin Buissink, MD, Academisch Siekenhuis, Maastricht, Holland; Liv Drolsum, MD, Department of Ophthalmology, Buskerud Sentralsykehus, Drammen, Norway; Philippe Dublineau, MD, Clinique de L’Esperence, Angers, France; Tom Eggert ¨ jenafdelning E, Odense University Hospital, Hansen, MD, O Denmark; Finn Eisgart, MD, Thisted, Denmark; Jan-Tjeerd de Faber, MD, Rotterdam Eye Hospital, Rotterdam, Holland; Ingrid Flore´n, MD, Department of Ophthalmology, Lund University Hospital, Lund, Sweden; Gian Maria Cavallini, MD, Instituto di Clinica Oculistica, Modena, Italy; Ype Henry, MD, AZVU, Amsterdam, Holland; Staale Hult¨ yeavd, Ullevål Sykegren, MD, Kristin Abrahamsen, MD, O ¨ jenafdelingen, hus, Oslo, Norway; Anne Klauber, MD, O So¨nderborg Sykehus, So¨nderborg, Denmark; Pavel Kuchynka, MD, Department of Ophthalmology, Vinohrady Teaching Hospital, Prague, Czech Republic; Slobodanka Latinovic, MD, University Eye Clinic, Clinical Center Novi Sad, Yugoslavia; Euge´nio Leite, MD, Department of Ophthalmology, University Hospital of Coimbra, Portugal; Mats Lundstro¨m, MD, Department of Ophthalmology, Blekinge Hospital, Karlskrona, Sweden; Daniela Nova´kova´, MD, Department of Ophthalmology, Teaching Hospital, Hradec Kralove, Czech Republic; Richard Packard, MD, FRCS, HRH Princess Christina’s Hospital, London, United Kingdom; Pitrova´ Sˇa´rka, MD, Private Eye Clinic, Ambulatory Service Lipa Centrum, Prague, Czech Republic; Lucia Scorolli, MD, Ottica Fisiopatologica, S’Orsola Hospital, Bologna, Italy; Helen Seward, FRCS, FRCOphth, Jonathan Eason, MD, Croydon Eye Unit, Mayday University Hospital, London, United Kingdom; Philippe Sourdille, MD, PierreYves Santiago, MD, Clinique Sourdille, Nantes, France; Ulf Stenevi, MD, Department of Ophthalmology, Gothenburg, Sweden; Nico Trap, MD, Polikliniek Oogheelkunde, Lorentz Ziekenhuis Zeist, Holland.

J CATARACT REFRACT SURG—VOL 27, AUGUST 2001